Intake/Exhaust Pressure Ratio's - what's the big deal?

[BoostedDrummer]

So I've been reading about this pressure ratio hype that people have been jawwing on about, something about making more power with a 1:1 pressure ratio in both the intake and exhaust manifolds or somethin'. I think this one feller with a slick fast Charger is the one raisin' heck about it. Don't you want a higher pressure and heat in the exhaust so you can spool that there turbo up right quick in a hurry? What's the big deal?

In all seriousness, what is the science behind trying to achieve an intake/exhaust pressure ratio of 1 to 1 or lower?

[glhs875]

So I've been reading about this pressure ratio hype that people have been jawwing on about, something about making more power with a 1:1 pressure ratio in both the intake and exhaust manifolds or somethin'. I think this one feller with a slick fast Charger is the one raisin' heck about it. Don't you want a higher pressure and heat in the exhaust so you can spool that there turbo up right quick in a hurry? What's the big deal?

In all seriousness, what is the science behind trying to achieve an intake/exhaust pressure ratio of 1 to 1 or lower?

Because, simply put, exhaust backpressure robs a lot of HP!

[A.J.]

Since the intake gasses are being pushed in with a compressor and the exhaust gasses are only being moved by the force of the piston, you don't want too much pressure in your exhaust manifold. Otherwise you can't get the fresh air/fuel mixture in because the exhaust gasses haven't had a chance to get out. So if you're boosting 20 psi you don't want 40 psi (1:2 ratio) in the exhaust. A 1:1 ratio would be 20 psi intake pressure and 20 psi exhaust manifold pressure.

On my SRT-4 van, I built a log header with a Chrylser flanged S60 turbo. I welded in an O2 bung in the end of it to measure back pressure in manifold, between the head and turbo. When I was boosting at 20 psi I had 25 psi measured in the exhaust manifold. From what I've read, that is really good for a street car. Street cars tend to be higher because they usually have smaller turbos to spool up quicker.

[BoostedDrummer]

Doesn't a higher pressure in the exhaust manifold spool the turbo up faster due to the high pressure trying to shoot out the turbine? Basic law of fluid dynamics is that high pressure will always try to flow to an area of lower pressure, so, that being said, wouldn't all of that pressure trying to escape into the exhaust downpipe have a faster velocity?

I made this thread for information purposes, in case anyone in the future is reading this and would ask the same questions. So, these would basically be laymans term questions lol.

[contraption22]

Not only does the backpressure itself cost horsepower, but it also can cause reversion when you want run a cam with a bit of overlap.

When the intake and exhaust valves are both open, high exhaust backpressure can be a hinderence to fresh air and fuel entering the chamber.

http://www.hotrod.com/how-to/engine/ctrp-1106-turbo-camshaft-guide/

[BoostedDrummer]

So for our turbocharged engines, it would be ideal to have a low exhaust pressure/high intake pressure in order to clear the cylinder for the next cycle? This is also where valve overlap comes into play? If there is a 1:1 ratio in the system, wouldn't the boost pressure still be fighting the exhaust backpressure as it tries to fill the cylinder? It would seem that having the lowest pressure ratio that is possible to achieve would only benefit the engine. By this, I mean that if there is 20 pounds pushing against 20 pounds, then it becomes neutral; wherein the only relief comes from the exhaust gasses exiting the turbine. Wouldn't the greater pressure from the turbo benefit by pushing out a smaller, lesser amount of pressure?

[acannell]

Pressure measured somewhere before the turbine wheel isn't necessarily generated by the turbine wheel. It can be head port, exhaust manifold, turbine wheel, swingvalve, exhaust system. Imagine a little straw as the exhaust manifold. Now you have a very high pressure differential between the exhaust valve and the turbine wheel but the flow is extremely low and very little power reaches the turbine wheel.

Since the exhaust system is connected to the atmosphere and the turbine wheel requires a source of power to spin the compressor wheel, there must be a pressure differential across it and the absolute pressure on the engine side of the turbo must be above atmospheric. So a ratio of 1:1 would mean for 25psi boost theres 25psi of pressure before the turbine (or somewhere before the turbine..not sure this is precisely defined as to measurement location).

[acannell]

So for our turbocharged engines, it would be ideal to have a low exhaust pressure/high intake pressure in order to clear the cylinder for the next cycle? This is also where valve overlap comes into play? If there is a 1:1 ratio in the system, wouldn't the boost pressure still be fighting the exhaust backpressure as it tries to fill the cylinder? It would seem that having the lowest pressure ratio that is possible to achieve would only benefit the engine. By this, I mean that if there is 20 pounds pushing against 20 pounds, then it becomes neutral; wherein the only relief comes from the exhaust gasses exiting the turbine. Wouldn't the greater pressure from the turbo benefit by pushing out a smaller, lesser amount of pressure?

I think if the pressure ratio goes below 1:1 then you have the intake charge being sucked out the exhaust during overlap = no bueno.

But this brings up a thought experiment:

Take a given compressor wheel.
Pick a certain amount of air to move through it for our thought experiment (will correspond to engine output power).
Pick a certain boost pressure for it to generate.
Assume atmospheric for the inlet pressure.
Now using the compressor map you can calculate how much power that work requires.

Now pick out your turbine wheel
Figure out how much air needs to flow through it and what pressure differential it needs to have in order to generate the power required by the compressor wheel above.
Assume the exit side of it is atmospheric.
Now you know what pressure the input side of it will need to be. Lets call it "turbine input pressure".

And it should be noted that the compressor and turbine in this thought experiment are linked only by a shaft. There is NO connection of the airstream between the two.

So where things get funny is when you power the turbine using an internal combustion engine. Now that "turbine input pressure" starts effecting how the cylinder fills because its attached to the cylinder, so you have to play a game to get it to be the right pressure (around the same as the pressure you are trying to fill the cylinder with). But also simultaneously you have to consider if your ICE will make the power you want at that turbine input pressure as boost pressure as a 1:1 ratio.

[Reaper1]

It takes a certain amount of work on the compressor wheel to deliver a certain flow rate (determined by physical properties of the compressor wheel, rpm, pressure). The work is imparted by the turbine as the turbine and the compressor are linked.

So, the exhaust energy is what has the potential energy to do the work. It is up to the turbine AND the turbine housing to convert that potential energy into mechanical energy.

If your intake/exhaust pressure ratio is 1:1, then the system is working very efficiently. If the ratio is higher than 1:1, that means there is more potential energy built up than the turbine can convert or needs to convert into mechanical energy to drive the compressor. At some point the turbine will not be able to convert all of the potential energy into the needed work to spin the compressor hard enough (make enough torque) and the potential energy overruns the efficiency of the system and power suffers due to the fact that all of the potential energy isn't being converted to mechanical energy, so it has to go somewhere. It basically backfeeds the system and starts to prevent more potential energy from entering the equation...so you see power fall off in the upper rpms of the engine, the engine isn't as responsive as it could/should be, boost can fall off.

[Shadow]

I think everyone is hitting upon it, you want to drive the turbine with the Least amount of restriction possible, while getting the job done. Anything more and you're disrupting the potential flow of the motor. Remember, Air Pump! So your #1 objective is still to move as much air through the motor as possible. You can't do that with too much restriction on the turbine side, there has to be a happy medium.

Think about the turbine like a paddle wheel in a river. That paddle wheel can only work properly when it is Balance to let enough water through to Not disrupt the flow of the river, but still take enough energy out of the flow to do the work. Try to make the wheel do more work by Restricting the river's flow, and the river ends up overflowing Before the paddle wheel because it Can't pass enough through.

Now, we have a closed system, it Can't overflow, so it builds up pressure. That pressure is Not helping the tubine wheel spin faster, because it's there from RESTRICTION. (it's trying to Overrun the system) What it ends up doing is slow the Entire system down, because now everything from the intake on can't flow as freely anymore.

So you're thinking about it Correctly when you say that the Important piece of the puzzle is the Greatest difference that you can create between the before and aft (pre turbine/ Aft turbine) pressures, but you don't want to do that by placing a restriction in the path of the motor as a whole.

You Want to do it by Removing as much restriction as you can AFTER the turbine! This is how you create the difference in pressures that = Great flow and Power!

[85boostbox]

Exactly what I was about to say.

Excessive back pressure before the turbine not only robs power from the engine and creates a cork, it also makes the turbo work harder to produce boost on the compressor side. I have read but have no real life experience and would take r&d ( rob can you possibly fill this in) that if you were creating let's say 15psi on the compressor sode , but 30psi in back pressure on the turbine side, you could be realistically creating 22.5 psi if you were to bring the ratio down to 1:1. (I hope this makes sense...)

I have seen cars drop lower than a 1:1 ratio and still create MORE power. How low can you go before you start flat lining, I have no idea. But as Rob stated, engines are air pumps. They need, want to FLOW!!!!!

[contraption22]

I don't think supercharged engines have any trouble making power with an excellent exhaust-to-intake pressure ratio.

[Shadow]

Exactly what I was about to say.

Excessive back pressure before the turbine not only robs power from the engine and creates a cork, it also makes the turbo work harder to produce boost on the compressor side. I have read but have no real life experience and would take r&d ( rob can you possibly fill this in) that if you were creating let's say 15psi on the compressor sode , but 30psi in back pressure on the turbine side, you could be realistically creating 22.5 psi if you were to bring the ratio down to 1:1. (I hope this makes sense...)

I have seen cars drop lower than a 1:1 ratio and still create MORE power. How low can you go before you start flat lining, I have no idea. But as Rob stated, engines are air pumps. They need, want to FLOW!!!!!

I prefer to think of it as how much more Power per lb of boost you can make vs how much more boost you will make.

So lets say @ 15psi intake boost and 30 psi drive pressure you are making an avaerage of 8hp/ lb of boost. Drop the drive pressure to 15 and now you're making 11-12hp/ lb of boost.

Make sense?

[85boostbox]

Yes. Had it in my brain, just suck at trying to figure out how to types stuff out.

[knownenemy]

Efficiency; the number 1 goal to work toward. :)

[Shadow]

Yes. Had it in my brain, just suck at trying to figure out how to types stuff out.

You are correct that it also allows for more boost. By it's very principle, running close to 1:1 will allow you to run out the compressor at whatever boost it is capable of sustaining against the rest of your build environment.

[85boostbox]

I'm actually surprised that no one has pointed out EGTs yet...

[Shadow]

I'm actually surprised that no one has pointed out EGTs yet...


EGTs are a very old school way of monitoring things and really don't come into play IF you're even in the ballpark of tuning and running any kind of decently thought out set-up.

I Almost ran an EGT gauge when we first started to get things going, but after reading all of the people melting down and gernading mtrs And EGT sensors failing, I decided to not run/ trust one. So, I proved to myself, if no one else, that IF your AFR's are in the "safe" range And you run the appropriate octane for your boost/ timing And your over-all setup is put together decently and well thought out, you really don't need to monitor EGT because it will simply never be an issue.

Having said that; Yes, EGT's will be lower when you run a better (closer to 1:1) pressure differential. (all other perameters being in check)

[Ondonti]

Sure you don't want to change slugs in the pits each run? ^^^

[85boostbox]

That is what I was meaning. With a 1:1 ratio your egt's will be lower and yet again, create more power.

[BoostedDrummer]

Doesn't a lower temperature EGT rob horsepower? Lower than normal I mean. I was under the impression that turbos like heat because its violent moving air that helps spin the turbine?

[Force Fed Mopar]

So what about if you had less than a 1:1 ratio? Like, say you have a external wastegate that can flow enough to act like open exhaust once the turbo has reached full spool. Would it drop the pressure or disrupt the flow so much that it would actually slow the turbo back down?

Or put another way, let's say you could get the same exhaust pressure as a supercharged car, as mentioned, which would (seemingly) obviously be lower than 1:1 due to less restrictive exhaust. Would the turbo still spin properly? Superchargers don't care about the ratio as they are crank driven, but I'm sure the turbo does.

[OmniLuvr]

I was under the impression that turbos like heat because its violent moving air that helps spin the turbine?

its not necessarily more violent, it is, but you have to look at heat as energy. if you have hot exhaust running through your manifolds it going to try and "expand" as it moves and eventually cools and looses its extra driving force farther down the exhaust stream as it transfers that energy into the exhaust pipe. now there is still "pressure" there at the end of the tail pipe, but with a little less energy behind it as it cools. so the more you keep your exhaust insulated the more energy you will have present until it starts to cool from distance or from the exhaust pipe itself. which brings up a good point, in which I don't like to wrap my downpipe (as long as its not going to burn something) to allow the exhaust to enter a lower/cooler pressure zone right out of the turbo...

[johnl]

As the exhaust gasses cool, their density increases. Dense gasses have more weight per unit of volume and may impart more energy to the the turbine than faster and hotter but less dense gasses.

[Rrider]

I would think you want it as close to 1:0 as you could get it.. I don't see how the exhaust side being too low could ever be a problem!

[85boostbox]

Nobody that I know has gotten extremely low. I think the lowest I have seen is 1.0/.7.

[OmniLuvr]

As the exhaust gasses cool, their density increases. Dense gasses have more weight per unit of volume

but how far would the exhaust have to travel or how "cool" would the temp have to be? and how would you take advantage of the more dense gasses? would you have to build a header/exhaust system that starts out "larger" in diameter to promote flow, then get smaller as it travels to the turbo to keep velocity up?

the rear mount turbo setups can work well, but they usually utilize a smaller than "usual" turbine/wheel and a larger wastegate and tend to wrap the complete exhaust to help with spool and still have flow, just food for thought...

[ShadowFromHell]

Some great info here for sure, but how would a guy apply this knowledge to a T2 car with the basic mods we all do?

[85boostbox]

Some great info here for sure, but how would a guy apply this knowledge to a T2 car with the basic mods we all do?

Actually most people do without even realizing it. That is why a lot of people misunderstand turbocharging. The biggest way to drop pressure ratio is actually AFTER the turbine. Aka downpipe exhaust. Rob has proved that time and time again and preaches it CONSTANTLY. He gets the most power he can out of the smallest turbine he can with his setup, even with the factory log manfold. And still pertains a 1:1 ratio. I'm using Rob as an example cause he is one of the very few that shares everything and hides nothing. plus his documentation on different stages of his car.

[shadow88]

Ok, so you open up the exhaust with a sewer sized swing valve and down pipe and a nifty exhaust cut out just to cover all the bases.

What would you suggest for head porting, valve size, cam selection, cylinder head design, turbine wheel sizing, turbine housing choices, compressor wheels and housings?

All the usual things people are trying to select to get the correct piece for the most power and ultimately whether they know it or not, ideal pressure ratio.

For example, say I just added an exhaust pressure gauge and I'm double my boost pressure.

I have a huge exhaust already, what else would you change?

[Shadow]

Ok, so you open up the exhaust with a sewer sized swing valve and down pipe and a nifty exhaust cut out just to cover all the bases.

What would you suggest for head porting, valve size, cam selection, cylinder head design, turbine wheel sizing, turbine housing choices, compressor wheels and housings?

All the usual things people are trying to select to get the correct piece for the most power and ultimately whether they know it or not, ideal pressure ratio.

For example, say I just added an exhaust pressure gauge and I'm double my boost pressure.

I have a huge exhaust already, what else would you change?

IF you had your exhaust all done with dump and all that could only happen with the smallest most miss-matched turbo possible. You could Not put any normal turbo configuration on and get that bad of a reading.

So you would need some kind of frankenstein mini, like a 50 trim T04e mated to a mitts turbine housing and wheel running 30psi through a highly efficient set-up.

[contraption22]

It's a careful balance of keeping back pressure low and velocity up before the turbine. After the turbine is much simpler, just make everything big.

[BoostedDrummer]

You'd think there'd be some limit to how "free" the exhaust has to be after the turbine though, right? Too big and you'd run the risk of boost spikes? I seem to remember reading somewhere that having too free flowing of an exhaust will leave the engine feeling gutless on the bottom end.

[1BADVAN]

You'd think there'd be some limit to how "free" the exhaust has to be after the turbine though, right? Too big and you'd run the risk of boost spikes? I seem to remember reading somewhere that having too free flowing of an exhaust will leave the engine feeling gutless on the bottom end.
From what I understand
no not on a turbo car, the bigger/"Free-er" the exhaust is post turbo just will help it spool faster. The issue of boost spikes is due to a wastegate that is insufficient, not because the big exhaust is bad, you could fix boost spikes with a small exhaust but you will also kill power. You probably did read that a free flowing exhaust will cause you to loose torque, but unless you are towing something, that doesn't matter, you want Horsepower. With a turbo car unless you have a huge turbine you will always have some backpressure wanted or not, due to the restriction of the turbo.

[85boostbox]

Boost spikes are usually associated with the sizes of wastegates. Usually not with the exhaust flow. That is why you see a lot of people on here port the waste gate hole for better control.

[85boostbox]

I should add as well that boost spikes can also be attributed to an undersized turbo and running out of breath on a setup.

[Shadow]

You'd think there'd be some limit to how "free" the exhaust has to be after the turbine though, right? Too big and you'd run the risk of boost spikes? I seem to remember reading somewhere that having too free flowing of an exhaust will leave the engine feeling gutless on the bottom end.

Garrett turbos (and most others I would imagine) are designed to run full open, No exhaust! So there is no such thing as too big ;)

What you read is a Myth. Power will Not suffer as your turbo will spool Faster, making More TQ down low, not less.

[shadow88]

Ok, how about I re do the question.

Let's say I have the typical set up, that's a 2.2l turbo 2 with a 2 piece, hybrid 50 trim stage 2 .63 housing and a 3 inch exhaust. I run 25 psi boost. Let's also say the pressure ratio is not 1:1, let's go with 1.5:1 as the revs climb to the upper end.

What can be done to reduce the pressure ratio closer to 1:1 regarding cam duration, lift,advance/ retard, port size, intake design, charge pipes, tb size or anything else you want to mention?

I'm trying to get an idea of things to help reach the "ideal" pressure ratio that isn't a different turbo.

[BoostedDrummer]

You could have the exhaust manifold ported to increase flow is about all I can think of aside from going with either the turbos unleashed log header or a tubular design.

[85boostbox]

Adding any more flow ( can, port work etc etc) is only going to add more pressure. What kind of swingvalve are you running?

[5DIGITS]

This is a GREAT thread as many of the items discussed are the issue that we realize when selecting a turbo, its boost level, the induction volume, induction pressure losses, turbine size, etc...

A few items worth mentioning:
Cam duration and/or over-lap 'falsely' manipulate the pressure ratio with respect to intake VS exhaust gas pressures.
'Falsely' because its manipulating trapping efficiency which does not address the true source of the imbalance.
For example, an excessive amount of over-lap can reduce the pressure ratio between intake and exhaust but is reducing back pressure due to reversion back into the combustion chamber.
Therefore the balance becomes, as mentioned, the port work and upstream/downstream set-up configuration.

The talent in playing this balancing act is the willingness to support trade-offs, for the most part.
If a 1:1 ratio is desired on a single turbo application, expect that it will come at the expense of lag, loss of low end torque, etc..
As the pressure ratio climbs, the inverse will occur.

With this, the larger the turbine side, turbine wheel, exhaust ports and supporting exhaust system - the closer you'll be to 1:1.
In contrast, it can also be accomplished by restricting the induction system, reducing cylinder pressures (via spark, boost, cam timing, etc..).
Therefore, it narrows down to how far anyone is willing to go and what the over-all performance expectation is while realizing its manipulation of one piece of a very large puzzle.

[contraption22]

Ok, how about I re do the question.

Let's say I have the typical set up, that's a 2.2l turbo 2 with a 2 piece, hybrid 50 trim stage 2 .63 housing and a 3 inch exhaust. I run 25 psi boost. Let's also say the pressure ratio is not 1:1, let's go with 1.5:1 as the revs climb to the upper end.

What can be done to reduce the pressure ratio closer to 1:1 regarding cam duration, lift,advance/ retard, port size, intake design, charge pipes, tb size or anything else you want to mention?

I'm trying to get an idea of things to help reach the "ideal" pressure ratio that isn't a different turbo.

The best thing you can do short of changing the turbo is make the exhaust plumbing post turbine as large as possible with as few bends as possible, and those bends should be as large and as wide as possible. It's also important to have an intake plumbing (pre and post compressor) that is as free flowing, yet thermally efficient. Any extra work that your compressor has to do results in more turbine back pressure.

The real gains come from picking a newer tech turbo that is much more mechanically and thermally efficient than the old T series.

[contraption22]

The talent in playing this balancing act is the willingness to support trade-offs, for the most part.
If a 1:1 ratio is desired on a single turbo application, expect that it will come at the expense of lag, loss of low end torque, etc..
As the pressure ratio climbs, the inverse will occur.

With this, the larger the turbine side, turbine wheel, exhaust ports and supporting exhaust system - the closer you'll be to 1:1.
In contrast, it can also be accomplished by restricting the induction system, reducing cylinder pressures (via spark, boost, cam timing, etc..).
Therefore, it narrows down to how far anyone is willing to go and what the over-all performance expectation is while realizing its manipulation of one piece of a very large puzzle.

Agreed. A 1:1 one ratio is a much more attainable goal for a race application, where you really don't care about low-rpm response too much. But it still remains that reducing turbine backpressure even from 3:1 to 2:1 would be a worthwhile effort.

[shadow88]

Thanks for the answer, I'm sure we're getting somewhere for the average guy.

As a disclaimer, I'm not interested in changing anything on my car, I don't have an exhaust pressure reading, nor do I really care. I have a satisfactory amount of lag as well as max power so I'm not changing much.

Thanks to 5 digits for mentioning that the closer the ratio gets to 1:1 the more turbo lag you will have. I know shadow liked to refer to that as "drive pressure" and it makes perfect sense it'll increase lag.

Now, the reason I chose the "typical" 2.2l set up is many people have this and may be looking to increase power and already spent $800 or more for the turbo and exhaust, so they're probably looking for anything else they could change, like cam advance/ retard, new cams on the market, tb size, charge pipes ect ect.

5 digits mentioned increased overlap leading to reversion, and if you didn't read the link contraption posted a couple days ago regarding cams, you really should. Maybe things like head flow comparison numbers or something like that the average person can use.

[contraption22]

Thanks to 5 digits for mentioning that the closer the ratio gets to 1:1 the more turbo lag you will have. I know shadow liked to refer to that as "drive pressure" and it makes perfect sense it'll increase lag.


I don't think he said or implied that. Certainly many of the steps one could take to reduce turbine backpressure would also improve turbo response. It really depends how bad your backpressure is to start with. Certainly you can free up your post-turbine exhaust and increase your charge cooling efficiency without increasing lag.

[shadow88]

I don't think he said or implied that. Certainly many of the steps one could take to reduce turbine backpressure would also improve turbo response. It really depends how bad your backpressure is to start with. Certainly you can free up your post-turbine exhaust and increase your charge cooling efficiency without increasing lag.

When I read 5 digits post, paragraph 3, that's what I get out of it.
The talent in playing this balancing act is the willingness to support trade-offs, for the most part.
If a 1:1 ratio is desired on a single turbo application, expect that it will come at the expense of lag, loss of low end torque, etc..
As the pressure ratio climbs, the inverse will occur.

Did I interpret this incorrectly?

[BoostedDrummer]

I think from what I understood reversion to be, is that during the overlap time when the exhaust and intake valves are both open, that when the exhaust pressure at the turbine is 30psi (this is all for example) and the intake pressure is only 15psi from the turbo (compressor), then reversion means that the 30psi will overcome the 15psi and force some of that hot exhausted air back into the intake. Sort of like an exhaust gas recirculation(EGR) situation, which we all know robs power and not to mention heats up the intake charge thats being delivered into the next combustion cycle. Now if the opposite were true, being 30psi intake/15psi exhaust, then the overlap would help blow out the gas that was just used during the combustion stroke out through the exhaust valve faster, being that 30psi overtakes 15psi. This would also cool the valves a bit I'd imagine.

Someone please correct me if I'm wrong, I was only a C+ student in high school lol

[shadow88]

You deserved higher marks in high school. That's how it works.

[contraption22]

When I read 5 digits post, paragraph 3, that's what I get out of it.
The talent in playing this balancing act is the willingness to support trade-offs, for the most part.
If a 1:1 ratio is desired on a single turbo application, expect that it will come at the expense of lag, loss of low end torque, etc..
As the pressure ratio climbs, the inverse will occur.

Did I interpret this incorrectly?

I think you did a little bit if you interpreted it to mean that a a better ratio definitely means more lag. Certainly the magical 1:1 ratio will be in more race oriented setups, but again you can move closer to that ideal by doing things that lower back pressure AND improve response.

[85boostbox]

Then there is the twin scroll setup which helps with overall response by concentrating pulses from same firing cylinders to spool the turbo and keep pressure down by not having other cylinders fighting over who gets out first. Reason why most manufacturers like Ford have strictly gone over to twin scroll technology.

And then there is the VNT/VGT. We all know what those do. Or you should lol.

[Shadow]

The talent in playing this balancing act is the willingness to support trade-offs, for the most part.
If a 1:1 ratio is desired on a single turbo application, expect that it will come at the expense of lag, loss of low end torque, etc..
As the pressure ratio climbs, the inverse will occur.



I just wrote a novel on why this is an old school Myth. Then the site Froze......AGAIN! Don't know how to check if it auto saved.

Regardless, Lag does NOT have to be a big concern IF you do it Right ;)

[acannell]

How do we know that the various engines running at low pressure ratios (i.e. 1:1) are seeing benefits besides those which would just be associated with drastically lowering exhaust restrictions?

In other words, couldnt this scenario be observed:

1- a given engine running at say 35psi plenum pressure, with an exhaust pressure at 50psi measured at the head port. (1.42:1)
2- that engine makes say 400hp
3- changes to the exhaust manifold and swingvalve are made to drastically reduce exhaust restrictions
4- at same 35psi plenum pressure, engine now makes 450hp, exhaust pressure is now 35psi at head port (1:1)

How do we know that extra 50hp gained isn't simply because now the engine isn't pushing ~800cfm at 15psi through the exhaust restrictions?

In other words, how do we know its simply reduction of the power required to force air through restrictions, versus special efficiencies gained by manipulating how the exhaust and intake charges directly interact during overlap?

For instance: it takes about 30hp to compress 400cfm of air from atmospheric to ~30psi. 400cfm is roughly 200hp at typical AFRs. So an engine consuming twice that much would take about twice as much power. So lets say it takes 60hp at 400hp to push the exhaust gases from valve seat to turbine input with around a 25psi drop, at 800cfm engine air filter air flow. So if we remove all those restrictions, and now that drop is 1psi, cant we claim thats where the 60hp comes from? Why do we conclude its coming from special efficiencies with the exhaust and intake interacting? We know that the restriction alone requires 50hp+ at 400hp+ power levels so how much benefit is left to assign to "neutral" effects of 1:1?

What exactly is the model of how the exhaust and intake charges supposedly interact during overlap at 1:1? If the pressures are the same then wouldn't the exhaust and intake have equal tendency to fill the cylinder as its volume increases, besides their different valve openings?

How do we know a 1:1 is actually 1:1 unless its measured directly behind the valve seats? If thats where the action of these special benefits are, then how can a 1:1 measurement made further downstream align with a model that explains things by describing pressures as 1:1 further upstream, where they certainly would be different than the pressure measured downstream?

[BoostedDrummer]

I've kind of thought about the pressure acting against eachother, but from my little knowledge, seems like the only time it is to be concerned is during the valve overlap period. Add to that you also have a changing "environment" going on as well(couldn't think of a better word to describe). By that I mean that the piston is also moving a volume of air just by its movement inside the cylinder. So what I would guess is that when the piston is driving upwords, it is creating an environment of increasing pressure even though it is expelling the exhaust gasses. When the intake valve opens during overlap, won't the piston in effect be trying to push some of the intake charge out?

[85boostbox]

I just wrote a novel on why this is an old school Myth. Then the site Froze......AGAIN! Don't know how to check if it auto saved.

Regardless, Lag does NOT have to be a big concern IF you do it Right ;)
I'll bite off of this "old school" myth. The old school myth was once true in my eyes. But look at technology compared to today to just 10 years ago. With advancements like we have now in technology and tuning lag can almost be eliminated with proper tuning. I helped tune my buddys Honda that had a WAY oversized turbo. Lag was horrendous and wasn't seeing boost til almost 4k. I tuned it he sees boost at 2500 now.

[contraption22]

How do we know that the various engines running at low pressure ratios (i.e. 1:1) are seeing benefits besides those which would just be associated with drastically lowering exhaust restrictions?

In other words, couldnt this scenario be observed:

1- a given engine running at say 35psi plenum pressure, with an exhaust pressure at 50psi measured at the head port. (1.42:1)
2- that engine makes say 400hp
3- changes to the exhaust manifold and swingvalve are made to drastically reduce exhaust restrictions
4- at same 35psi plenum pressure, engine now makes 450hp, exhaust pressure is now 35psi at head port (1:1)

How do we know that extra 50hp gained isn't simply because now the engine isn't pushing ~800cfm at 15psi through the exhaust restrictions?

In other words, how do we know its simply reduction of the power required to force air through restrictions, versus special efficiencies gained by manipulating how the exhaust and intake charges directly interact during overlap?

For instance: it takes about 30hp to compress 400cfm of air from atmospheric to ~30psi. 400cfm is roughly 200hp at typical AFRs. So an engine consuming twice that much would take about twice as much power. So lets say it takes 60hp at 400hp to push the exhaust gases from valve seat to turbine input with around a 25psi drop, at 800cfm engine air filter air flow. So if we remove all those restrictions, and now that drop is 1psi, cant we claim thats where the 60hp comes from? Why do we conclude its coming from special efficiencies with the exhaust and intake interacting? We know that the restriction alone requires 50hp+ at 400hp+ power levels so how much benefit is left to assign to "neutral" effects of 1:1?

What exactly is the model of how the exhaust and intake charges supposedly interact during overlap at 1:1? If the pressures are the same then wouldn't the exhaust and intake have equal tendency to fill the cylinder as its volume increases, besides their different valve openings?

How do we know a 1:1 is actually 1:1 unless its measured directly behind the valve seats? If thats where the action of these special benefits are, then how can a 1:1 measurement made further downstream align with a model that explains things by describing pressures as 1:1 further upstream, where they certainly would be different than the pressure measured downstream?


I kinida see your reasoning of the question for the sake of discussion, but when it comes down to it, we know exhaust backpressure a detriment to power. Regardless of theory behind the motivation to remove or reduce it, the end result of reducing backpressure is more power.

[acannell]

I kinida see your reasoning of the question for the sake of discussion, but when it comes down to it, we know exhaust backpressure a detriment to power. Regardless of theory behind the motivation to remove or reduce it, the end result of reducing backpressure is more power.

Concluding that reducing exhaust restrictions = good and leaving it at that doesn't really address the question in the thread title.

[contraption22]

Concluding that reducing exhaust restrictions = good and leaving it at that doesn't really address the question in the thread title.

True enough. Did you read the Hot Rod article about camshafts for turbo cars?

[acannell]

Heres the R5 cam as measured by turbo2point2 and 4Lbodies. Also on the plot is the piston location.

Maybe the R5 is a bad example for this discussion for some reason (low overlap?). But anyways:

Look at how long the exhaust pressure has to influence the cylinder volume.

When the piston stops moving upwards on the exhaust stroke and is at TDC at the beginning of the intake stroke, the exhaust and intake valves are both open about 0.025".

At that time the cylinder volume is at its minimum, basically combustion chamber + piston dish sized.

This is the time where exhaust gases will possibly "influence" the intake charge and/or its influence on the cylinder volume.

At say 3500 rpm, the crank is turning once every 17 ms.

In about 25 crankshaft degrees from that TDC, the exhaust valve is fully closed.

That takes about 1 millisecond.So we are talking about how much the exhaust system pressure can influence the cylinder volume (basically ~50cc's at that point in time), with a valve open 0.025", in 1 thousandth of a second.

How much does an exhaust port flow, backwards, at 0.025" lift? Maybe 150cfm at 1bar at 0.5" lift. At 0.025" lift..maybe 15cfm? Thats about 7000cc's per second. So in our 1 millisecond, thats about 7 cc's. Maybe double that if our absolute pressure is 30psi in the exhaust manifold versus 0 in the cylinder.

But remember, the exhaust valve is CLOSING. So its only 0.025" for that one instant in time. So without doing the integration I'd say that we are looking at the exhaust pressure possibly filling up the combustion chamber with single digit cc's of exhaust. Compared to the maximum cylinder volume at BDC something less than 1%. How much can that really matter?

http://i242.photobucket.com/albums/ff197/acannell/r5wpiston_zps5522acee.jpg (http://s242.photobucket.com/user/acannell/media/r5wpiston_zps5522acee.jpg.html)

[acannell]

True enough. Did you read the Hot Rod article about camshafts for turbo cars?

im not sure if it was posted in one of these TM threads probably

to be clear I think reducing exhaust pressure (and therefore pressure ratio) is obviously a good thing

but what I'm trying to focus on is whether the benefits come simply from those restrictions not consuming power directly, versus the benefits coming from some kind of special efficiency gained in the combustion chamber from intake and exhaust pressures interacting

If the benefits are just from the reductions in backpressure no longer consuming power then I dont think there is any need to focus on a specific "ratio", since really it would just be a matter of reducing exhaust restrictions period, without reference to matching boost pressure.

[acannell]

wait a second...

The cylinder is already filled with exhaust at TDC of the exhaust stroke. Its just exhaust that hasn't been pushed out. When the piston is at TDC there is still a combustion chamber volume left and that volume is filled with exhaust.

So the idea that exhaust gases are flowing back into the cylinder during overlap doesn't really make sense. Its already filled with exhaust gas. And exhaust gas that is above exhaust manifold pressure at least until exhaust stroke TDC and then probably at least equal to exhaust manifold pressure for several crank degrees until the volume of the cylinder increases again on the intake stroke, enough to reduce that pressure.

[contraption22]

im not sure if it was posted in one of these TM threads probably
.

It's stickies, but also in post #5 of this thread.

[Force Fed Mopar]

Seems to me like the wastegate is the area to look at to reduce the drive pressure ratio without changing the turbo. Either in porting the internal wastegate hole or by adding an external wg that flows more.

As I asked earlier, what if (in theoretical design, not sure if it is actually possible) you could get a header and external wg ( or two) that would flow enough exhaust once open to lower the ratio below 1:1? Is this still improving things, or is it reducing the turbine drive pressure and causing boost stability issues?

[5DIGITS]

Regardless, Lag does NOT have to be a big concern IF you do it Right ;)

Well said !.. in addition "or drive it right!"



There was also mention within the thread about opening the WG hole to reduce back pressure.
This is only true when the demanded exhaust flow exceeds available flow across the scroll area plus the WG hole, with the flapper near or at full extension.
Otherwise, all that's accomplished by doing so (opening the WG hole) is altering the operating position of the valve because the boost will learn to close the valve, to obtain the same boost previously realized with the smaller hole.
Therefore, depending on the boost being used and the resulting exhaust demands, you end up with the same back pressure until the turbine limit is exceeded.


This leads into the turbine housing 'game'.
The game consists of where the flow is desired 'WG/bypass OR turbine scroll'?
Imagine that if a very small turbine wheel is used with a stock .48 turbine housing, the flow demand will shift to the WG hole because the scroll housing area and related exducer diameter will not support the flow alone.
Likewise, the reflective approach is a larger housing and wheel which now minimizes the WG flow demand because the scroll area can now supports the required flow and excessive WG porting cannot be completely justified.
This is ultimately the difference in approach when comparing the 2.2 of "yesteryear" to the SRT 2.4 of recent year.
One realizes higher BP at low RPM to obtain quick response BUT minimizes upper RPM restriction when the WG opens.
The other maintains lower BP throughout the RPM range and relies on minimal WG activity to control the target boost level.

Two different approaches that can be set up in a way that produce the same exhaust BP levels but with completely different boost response curves.
Which approach is required is largely dictated by the size (area and wheel mass) of the compressor and the energy required to get the process started and maintained.

[acannell]

Seems to me like the wastegate is the area to look at to reduce the drive pressure ratio without changing the turbo. Either in porting the internal wastegate hole or by adding an external wg that flows more.

As I asked earlier, what if (in theoretical design, not sure if it is actually possible) you could get a header and external wg ( or two) that would flow enough exhaust once open to lower the ratio below 1:1? Is this still improving things, or is it reducing the turbine drive pressure and causing boost stability issues?

Answering this sort of question in a way that can direct design requires more formal analysis than I've ever seen on TM or TD. I dont think we're there yet. When you see overlaid efficiency lines on compressor AND turbine maps linking the two at certain operating points then we're there. Never seen that on an internet forum.

But to speak about it in the usual generalities, theres no such thing as "turbine drive pressure". There is pressure drop across the turbine, and mass flow rate through the turbine. Those two things generate the shaft power to drive the compressor. If the post turbine restriction is reduced to 0 and you have essentially atmospheric right at the turbine blades at the output, I dont see why you wouldn't be able to continue to modulate turbine power by bypassing exhaust around it. Less gas through the turbine = less power. I think any sort of boost control stability problems are going to have a more complex cause.

To prove this you could split the exhaust stream in two and run two turbos each at half the power. So there shouldn't be some reason you cant control shaft power.

[85boostbox]

Answering this sort of question in a way that can direct design requires more formal analysis than I've ever seen on TM or TD. I dont think we're there yet. When you see overlaid efficiency lines on compressor AND turbine maps linking the two at certain operating points then we're there. Never seen that on an internet forum.

But to speak about it in the usual generalities, theres no such thing as "turbine drive pressure". There is pressure drop across the turbine, and mass flow rate through the turbine. Those two things generate the shaft power to drive the compressor. If the post turbine restriction is reduced to 0 and you have essentially atmospheric right at the turbine blades at the output, I dont see why you wouldn't be able to continue to modulate turbine power by bypassing exhaust around it. Less gas through the turbine = less power. I think any sort of boost control stability problems are going to have a more complex cause.

To prove this you could split the exhaust stream in two and run two turbos each at half the power. So there shouldn't be some reason you cant control shaft power.
As stated earlier and in your last paragraph, twin scroll technology is pretty much 2 turbine housings, powering one compressor wheel.

[Shadow]

Seems to me like the wastegate is the area to look at to reduce the drive pressure ratio without changing the turbo. Either in porting the internal wastegate hole or by adding an external wg that flows more.

As I asked earlier, what if (in theoretical design, not sure if it is actually possible) you could get a header and external wg ( or two) that would flow enough exhaust once open to lower the ratio below 1:1? Is this still improving things, or is it reducing the turbine drive pressure and causing boost stability issues?

Any attempt to increase W/G flow will result in lower boost, there are No two ways around it. The only exception I know of is Dedicated W/G positioning using a deliberately Smaller turbine housing/ wheel that normal to get Great response down low, then Good top end flow when the exhaust drive pressure overruns the turbine and flows through the Dedicated W/G. AFAIK this will Not Increase top end power significantly over a properly sized turbine application, but it Will give Better response down low.

[Shadow]

There was also mention within the thread about opening the WG hole to reduce back pressure.
This is only true when the demanded exhaust flow exceeds available flow across the scroll area plus the WG hole, with the flapper near or at full extension.
Otherwise, all that's accomplished by doing so (opening the WG hole) is altering the operating position of the valve because the boost will learn to close the valve, to obtain the same boost previously realized with the smaller hole.
Therefore, depending on the boost being used and the resulting exhaust demands, you end up with the same back pressure until the turbine limit is exceeded.


This leads into the turbine housing 'game'.
The game consists of where the flow is desired 'WG/bypass OR turbine scroll'?
Imagine that if a very small turbine wheel is used with a stock .48 turbine housing, the flow demand will shift to the WG hole because the scroll housing area and related exducer diameter will not support the flow alone.
Likewise, the reflective approach is a larger housing and wheel which now minimizes the WG flow demand because the scroll area can now supports the required flow and excessive WG porting cannot be completely justified.
This is ultimately the difference in approach when comparing the 2.2 of "yesteryear" to the SRT 2.4 of recent year.
One realizes higher BP at low RPM to obtain quick response BUT minimizes upper RPM restriction when the WG opens.
The other maintains lower BP throughout the RPM range and relies on minimal WG activity to control the target boost level.

Two different approaches that can be set up in a way that produce the same exhaust BP levels but with completely different boost response curves.
Which approach is required is largely dictated by the size (area and wheel mass) of the compressor and the energy required to get the process started and maintained.

Agreed, and back to the comment I made on Drive pressure vs lag. (now that I can type freely :))

My first post (the novel) was an Inspired Mona Lisa, unfortunately that only happens once, so you guys will have to make due with the dummied down version.

In a nut shell, If you attempt to use A/R and turbine wheel size to correct drive pressure, you Will most definitely Suffer from turbo Lag. This is what most have done and were doing back when I first got involved with turbocharging.

So what did I do? I decide to use the Smallest turbine housing/ wheel combo I could in order to achieve desired Power level (Pressure differential be damned!) but make the Intake and exhaust Outlet as Efficient as I possibly could.

Did I Know I was heading down the path to 1:1 differential with Phenomenal street drivability? Nope! Had no clue. Until I installed the drive pressure gauge I would have thought the drive pressure in the Charger would have been at Least 2:1. I was Shocked to say the least, but it showed me that Not only does it work, it works Better than I had Ever imagined!

Remember, when I ran the 4" intake everyone said it was severe overkill. When I showed the 4" downpipe, same response. When I said I could make over 500WHP from the 9cm turbine housing on the holset (.65 A/R) they all said it was Way too small and that I would Lose top end power because of the tiny turbine housing and wheel.

Pretty sure, even to this day, that the Charger has one of, if not The Higher top end 1/4 mile Charger of Any 8v TD/ TM I know of. Add to this that the transient response is so mind boggling to those who I have take for rides that they say the car has No Lag, and How is this Possible.

So, Again, as much as most like to Think the charger is a laggy Drag car, it is actually the Complete opposite. Which Proves that you Can have a 1:1 differential and Great transient response IF you do it Right! (and yes, Know how to Drive a turbo car! :)) :)

[Force Fed Mopar]

Agreed, and back to the comment I made on Drive pressure vs lag. (now that I can type freely :))

My first post (the novel) was an Inspired Mona Lisa, unfortunately that only happens once, so you guys will have to make due with the dummied down version.

In a nut shell, If you attempt to use A/R and turbine wheel size to correct drive pressure, you Will most definitely Suffer from turbo Lag. This is what most have done and were doing back when I first got involved with turbocharging.

So what did I do? I decide to use the Smallest turbine housing/ wheel combo I could in order to achieve desired Power level (Pressure differential be damned!) but make the Intake and exhaust Outlet as Efficient as I possibly could.

Did I Know I was heading down the path to 1:1 differential with Phenomenal street drivability? Nope! Had no clue. Until I installed the drive pressure gauge I would have thought the drive pressure in the Charger would have been at Least 2:1. I was Shocked to say the least, but it showed me that Not only does it work, it works Better than I had Ever imagined!

Remember, when I ran the 4" intake everyone said it was severe overkill. When I showed the 4" downpipe, same response. When I said I could make over 500WHP from the 9cm turbine housing on the holset (.65 A/R) they all said it was Way too small and that I would Lose top end power because of the tiny turbine housing and wheel.

Pretty sure, even to this day, that the Charger has one of, if not The Higher top end 1/4 mile Charger of Any 8v TD/ TM I know of. Add to this that the transient response is so mind boggling to those who I have take for rides that they say the car has No Lag, and How is this Possible.

So, Again, as much as most like to Think the charger is a laggy Drag car, it is actually the Complete opposite. Which Proves that you Can have a 1:1 differential and Great transient response IF you do it Right! (and yes, Know how to Drive a turbo car! :)) :)

And this is still on the stock exhaust manifold, correct? And stock Holset internal WG?

[85boostbox]

I know Rob still runs the ported stocker, and I "think" the internal gate too.

[Shadow]

And this is still on the stock exhaust manifold, correct? And stock Holset internal WG?

Correct. My own stock ported exhaust mani and stock untouched Holset W/G hole with tension on W/G actuator set to minimum.

[OmniLuvr]

stock untouched Holset W/G hole

but I do think you have hinted to the fact that you may need to port the wastegate hole soon, as you seamed to have a small amount of boost creep when running the 12" long 4" dump...

[Pat]

Rob...where are you tapped for pre turbo pressure? At the manifold collector?

[Shadow]

but I do think you have hinted to the fact that you may need to port the wastegate hole soon, as you seamed to have a small amount of boost creep when running the 12" long 4" dump...

It Will creep at lower boost with the dump open. (below 25psi) but I only open the dump at the track, so really not an issue. I am considering porting it to bring down my minimum street boost setting Back to around 18psi. Right now it's around 22 and while that's fine for 93-94 octane, I get some knock on 91 and 91 is becoming the common Premium fuel around here.

- - - Updated - - -


Rob...where are you tapped for pre turbo pressure? At the manifold collector?

Yes, manifold collector right at the flange to the turbo.

[OmniLuvr]

It Will creep at lower boost with the dump open. (below 25psi) but I only open the dump at the track, so really not an issue

gotcha! I remember you talking about it a while ago, it was in a good thread where I learned a lot of things, very good info from you, just cant remember which one it was? (prob 4 years ago?)

[Force Fed Mopar]

So the main factor in drive pressure seems to indeed be turbine selection...

[Shadow]

So the main factor in drive pressure seems to indeed be turbine selection...


Doesn't a higher pressure in the exhaust manifold spool the turbo up faster due to the high pressure trying to shoot out the turbine? Basic law of fluid dynamics is that high pressure will always try to flow to an area of lower pressure, so, that being said, wouldn't all of that pressure trying to escape into the exhaust downpipe have a faster velocity?


THIS^^^^^

Is what I would consider the main factor in getting and keeping your drive pressure in check. You want the Greatest pressure differential right after the turbine. So whatever your drive pressure is (pre-turbine), let's say 20psi, if you could, you would shoot for Zero psi in the downpipe.

As the downpipe back pressure increases, the exhaust mani drive pressure Will Increase exponentially, causing the entire system to "back up" and lose power.

Just keep in mind that you want to attain this while keeping the intake vs exhaust mani ratio as close to 1:1 as possible.

And for those who are wondering, 1.5 : 1 is Not that bad ;) (there are Freaks out there that think 6 : 1 is OK lol)

[Reaper1]

Keep in mind that the turbine housing A/R ratio is only part of the equation when talking about turbine efficiency and how it uses the mass flow. The design of the turbine nozzle affects the angle and the velocity at which the flow hits the turbine blades. This can have a significant impact on turbo response and turbine flow/efficiency.

The turbine wheel itself is also very important as the aerodynamics of the blades can have a significant impact on mass flow out of the turbine, how efficient the gas can do work to the turbine, turbo response...and I'm sure I'm forgetting something right now.

Anyway, the point I'm trying to make is the turbine of a turbo is a system, just like everything else in the engine.

[acannell]

Keep in mind that the turbine housing A/R ratio is only part of the equation when talking about turbine efficiency and how it uses the mass flow. The design of the turbine nozzle affects the angle and the velocity at which the flow hits the turbine blades. This can have a significant impact on turbo response and turbine flow/efficiency.

The turbine wheel itself is also very important as the aerodynamics of the blades can have a significant impact on mass flow out of the turbine, how efficient the gas can do work to the turbine, turbo response...and I'm sure I'm forgetting something right now.

Anyway, the point I'm trying to make is the turbine of a turbo is a system, just like everything else in the engine.

Yes good point. Has anyone seen a turbine/housing map for any of our typical turbos? I know there are compressor maps but Ive not seen a turbine map.

[Reaper1]

The Holset EFR series has both their compressor and turbine maps on their website last I checked.

[85boostbox]

I'm still surprised that no one has really touched the subject on twin scroll stuff.

[Shadow]

I'm still surprised that no one has really touched the subject on twin scroll stuff.

Twin scroll = Way more $'s and time to make it worth doing + a Vast amount of knowledge to do it Right. Most twin scroll set-ups will suffer and get destroyed on the top end by single scroll turbo set-ups. IF I thought it was worth it, I would have gone that route looking for the Best response on the street.

So for now, anything under 700WHP and there are single scroll turbos that work just fine.

[ShadowFromHell]

What kind of gauges/setups are you guys using to monitor drive pressure? Just a normal boost gauge? What about heat? Ive got a boost only 40psi gauge I bought for my diesel I never used. Would that work? What about the heat?

[acannell]

What kind of gauges/setups are you guys using to monitor drive pressure? Just a normal boost gauge? What about heat? Ive got a boost only 40psi gauge I bought for my diesel I never used. Would that work? What about the heat?

Im using a pressure sensor but a gauge should work just fine. To deal with heat you can connect the gauge/sensor via a section of copper tubing to the point on the exhaust you want to measure. The tubing acts as a heat sink. I used a pretty short section which might be a little too short. Perhaps a longer section would be more appropriate. You are measuring pretty slow pressure changes so it shouldnt matter.

I have mine measuring pressure right after the head port so it doesn't tell me how much the manifold, turbo, swingvalve, or exhuast pipe are individually contributing, but it does tell me what the "pressure ratio" is from boost to exhaust pressure. Not at the valve seat but at least as near as I can at the moment. Good enough to ballpark the situation I think.

http://www.turbododge.com/forums/f4/f279/728610-1990-dodge-daytona-es-turbo-2-a.html#post3571297

[zin]

Put a loop in the copper/metal line going to the gauge, it helps to isolate the heat.

Mike

[Reaper1]

Twin scroll = Way more $'s and time to make it worth doing + a Vast amount of knowledge to do it Right. Most twin scroll set-ups will suffer and get destroyed on the top end by single scroll turbo set-ups. IF I thought it was worth it, I would have gone that route looking for the Best response on the street.

So for now, anything under 700WHP and there are single scroll turbos that work just fine.

I don't agree with this at all. Why is a twin scroll so much harder to do? If you are trying to keep the stock type exhaust manifold, then yeah, I agree. But, if you are going to go to a twin scroll then chances are you are also going to make a custom header. To make one for a twin scroll versus a single scroll only takes planning and not converging all of the tubes into one outlet like a typical header collector.

There are different ways to set-up the wastegates on twin scroll turbos. Maybe that's where you are thinking this gets complicated/expensive versus a single scroll. Having said that, the wastegate set-up doesn't have to be any more complicated than a single scroll. The most obvious way to do it is use 2 external wastegates. Yes, this is complicated, expensive, heavy, bulky and arguably not needed. This sort of set-up will be found mostly on money-is-no-object, b@lls-out, probably sponsored, full tilt race car. Think over 1000whp as a base for something like this. A twin scroll can absolutely be set-up with a single wastegate just like a single scroll. This is not only acceptable, but is done quite a bit for all of the reasons I just listed. Lastly there is the internal wastegate option, however very few twin scroll turbos have an internal gate, and only the BW EFR seems to be the only twin scroll performance option that I can remember off the top of my head.

Twin scroll turbine sections have the potential to outperform a similar single scroll turbine. However, there are still trade-offs and there isn't a direct correlation between what size twin scroll will give the best performance over a single scroll (meaning a decrease in spool time and keeping the same top end). From what I've read the "rule of thumb" is that you can typically run 1 size larger AR twin scroll than the single scroll size you would typically run. To put that in TM terms: if you are running a single scroll .63, you could run a .84 twin scroll (in theory) and get better spool while keeping the top end. Obviously in practice this will be different, but most of the reviews I've seen of people that have switched to a twin scroll have nothing but good things to say.

Please keep in mind that running a twin scroll turbine on an exhaust header/manifold designed for a single scroll will not net a performance gain (be very general here). You HAVE to run a manifold/header designed for a twin scroll turbine.

[85boostbox]

When I get home I will type on an actual computer. But Chris I agree with what you said.

[Shadow]

I don't agree with this at all. Why is a twin scroll so much harder to do?

if you are going to go to a twin scroll then chances are you are also going to make a custom header.

The most obvious way to do it is use 2 external wastegates. Yes, this is complicated, expensive, heavy, bulky and arguably not needed. This sort of set-up will be found mostly on money-is-no-object, b@lls-out, probably sponsored, full tilt race car.

A twin scroll can absolutely be set-up with a single wastegate just like a single scroll. This is not only acceptable, but is done quite a bit for all of the reasons I just listed. Lastly there is the internal wastegate option, however very few twin scroll turbos have an internal gate, and only the BW EFR seems to be the only twin scroll performance option that I can remember off the top of my head.

However, there are still trade-offs and there isn't a direct correlation between what size twin scroll will give the best performance over a single scroll (meaning a decrease in spool time and keeping the same top end.

Please keep in mind that running a twin scroll turbine on an exhaust header/manifold designed for a single scroll will not net a performance gain (be very general here). You HAVE to run a manifold/header designed for a twin scroll turbine.

You've already answered your own Q bro ;)

My HE351 internally gated turbo and stock exhaust mani vs anything you build twin scroll. You will spend at least 4x as much $'s, 4x as much time installing and 4x as much time getting all to work properly IF you chose everything right in the first place.

So like everything else, I'm Not saying it can't be done And work well. Just not worth the time and effort to Me, when I can build something so simple that Works at least 90% as good as the Best you could ever hope for out of a twin scroll set-up. :nod:

[Reaper1]

I agree that this (sticking with a single scroll and stock exhaust manifold) seems to work for you. You have the skills it seems to eek out every last drop of potential out of the stock exhaust manifold. Very few can do that and even by your own admission it isn't the easiest or best way to accomplish making power. Remember, the discussion is about why the intake/exhaust pressure ratio is such a big deal and it has morphed into how to mitigate the compromises to accomplish a more efficient pressure ratio.

More and more people are building or are having custom headers built nowadays in our community, so I believe that taking a look at the twin scroll option is not only valid, but more pertinent than it ever has been for us. On top of that it gives a whole new slew of options for turbine housings and just might help fill in some gaps in compromises, namely spool time versus top end flow. Does it make sense for everyone? No. Do I think that a twin scroll set-up would make a huge performance difference with the Charger? No. However, dismissing it totally as an option because single scrolls work is kind of limiting.

As far as a single scroll working 90% as well as a twin scroll....I buy that...but that last 10% might just be what puts me that car length ahead or lets me get on power that much sooner out of a corner. Do I honestly believe I'm on that level? LMAO...HELL NO (helps to have a running car to be on any kind of competing level)! However, it is a valid point, regardless of how far fetched.

[acannell]

You have the skills it seems to eek out every last drop of potential out of the stock exhaust manifold.

Where things get interesting is what exactly was done to do that. I would think the following components would be the most relevant:

-head
-intake
-swingvalve
-turbo
-camshaft

And in Shadows, case, from what I gather:

-head = G head with very light port work and +1mm valves
-intake = Heavily modified intake, but essentially just BIG
-swingvalve = Custom swingvalve modified to be BIG
-turbo = holset, not sure if the wheels in it are special or not
-camshaft = off-the-shelf F4

These would seem to be fairly straightforward modifications. I'm not saying Shadow does not have extra-ordinary skill, on the contrary, I would say his Charger is a prime example of resourcefulness and efficiency of $$$ and effort. He is very frequently describing his strategies as being the least effort requiring and the least $$$ requiring. So I dont see how whatever it is he did to use the stock manifold is somehow beyond the scope of what others could duplicate, besides the fact that people seem to ignore what hes telling them lol

More and more, Shadows build is seeming to me to be more and more pragmatic and doing away with unnecessary fantasies that so many people seem to think are absolutely required. From that perspective I think we should be looking at his Charger as a model for how to build a very fast race car with the absolute minimum wasted skill and effort. The skill in this case is knowing where to put the scalpel and cut away the fat.

[GLHS60]

Well said!!

Thanks
Randy


Where things get interesting is what exactly was done to do that. I would think the following components would be the most relevant:

-head
-intake
-swingvalve
-turbo
-camshaft

And in Shadows, case, from what I gather:

-head = G head with very light port work and +1mm valves
-intake = Heavily modified intake, but essentially just BIG
-swingvalve = Custom swingvalve modified to be BIG
-turbo = holset, not sure if the wheels in it are special or not
-camshaft = off-the-shelf F4

These would seem to be fairly straightforward modifications. I'm not saying Shadow does not have extra-ordinary skill, on the contrary, I would say his Charger is a prime example of resourcefulness and efficiency of $$$ and effort. He is very frequently describing his strategies as being the least effort requiring and the least $$$ requiring. So I dont see how whatever it is he did to use the stock manifold is somehow beyond the scope of what others could duplicate, besides the fact that people seem to ignore what hes telling them lol

More and more, Shadows build is seeming to me to be more and more pragmatic and doing away with unnecessary fantasies that so many people seem to think are absolutely required. From that perspective I think we should be looking at his Charger as a model for how to build a very fast race car with the absolute minimum wasted skill and effort. The skill in this case is knowing where to put the scalpel and cut away the fat.

[Reaper1]

What you don't see or know about Shadow's set-up is exactly what is done. You could throw that same combination together and only make 300hp. The combination is VERY important, but just as important are all the details into that combination. I could be wrong, but for some reason I remember there being several iterations of his exhaust manifold. Now, does it work well because it is hogged out, or because of some little tricks done to the runner entrances and the collector area? How balanced are the cylinders (meaning that clearly they are all running well enough, but how far from optimal are they running as a result of using the stock manifold)?

Head porting...we all know there's more to this than just making the holes bigger. What work was really done? What about the chambers?

The intake, turbo, and such are all well documented.

Now, the real difference....the actual tune in the computer. Simply saying it's "x-stage" or it was done by "x-person" means squat. Every car and every combo has different needs. Again, you could build the spitting twin to Rob's car and it STILL will require some slight tweaks that are different from his car and they STILL won't perform exactly the same.

Rob has been refining his car, his tune, and his set-up for a long time. I'm not calling Rob out or bashing him at all. I am not saying that his set-up isn't a good template to follow. However, a person needs to understand WHY his set-up is the way it is; he has the goal of going the fastest he can on as many stock or modified stock parts as possible....only changing parts out as needed for reliability, wear, drivability, or weight. It really is the epitome of doing the most with the stock parts in our community (that I know of). However, that doesn't mean that there isn't easier or better (not necessarily cheaper) ways to accomplish the same thing. Just because something uses the stock parts and is cheap doesn't mean it was easy. There's a reason there isn't a ton of 500hp TM's running stock exhaust manifolds.

[acannell]

What you don't see or know about Shadow's set-up is exactly what is done. You could throw that same combination together and only make 300hp. The combination is VERY important, but just as important are all the details into that combination. I could be wrong, but for some reason I remember there being several iterations of his exhaust manifold. Now, does it work well because it is hogged out, or because of some little tricks done to the runner entrances and the collector area? How balanced are the cylinders (meaning that clearly they are all running well enough, but how far from optimal are they running as a result of using the stock manifold)?

Head porting...we all know there's more to this than just making the holes bigger. What work was really done? What about the chambers?

The intake, turbo, and such are all well documented.

Now, the real difference....the actual tune in the computer. Simply saying it's "x-stage" or it was done by "x-person" means squat. Every car and every combo has different needs. Again, you could build the spitting twin to Rob's car and it STILL will require some slight tweaks that are different from his car and they STILL won't perform exactly the same.

Rob has been refining his car, his tune, and his set-up for a long time. I'm not calling Rob out or bashing him at all. I am not saying that his set-up isn't a good template to follow. However, a person needs to understand WHY his set-up is the way it is; he has the goal of going the fastest he can on as many stock or modified stock parts as possible....only changing parts out as needed for reliability, wear, drivability, or weight. It really is the epitome of doing the most with the stock parts in our community (that I know of). However, that doesn't mean that there isn't easier or better (not necessarily cheaper) ways to accomplish the same thing. Just because something uses the stock parts and is cheap doesn't mean it was easy. There's a reason there isn't a ton of 500hp TM's running stock exhaust manifolds.

Its not clear to me what your conclusion is. That someone planning a 500hp build should add the expense, complexity, and reduced reliability of a tubular manifold when theres proof that isnt required? How does that make sense? How is that easier? You dont suddenly reduce the requirement to tune or tweak because you bolt on a tubular header, if anything you need to have an even firmer grip on whats going on and be prepared to do even more trial and error testing to get it to work right. Or at least, the argument could equally be made in that respect until proven otherwise.

In other words all the stuff Rob may or may not have done to the Charger comes with the territory at that power level, I dont think there is enough data to attach it specifically to using a stock exhaust manifold.

[Shadow]

FTR, the Holset turbo is an HE351 with both stock compressor and turbine wheels, albeit the turbine wheel has been clipped. (I believe it was 7 deg but would need to double check)

[OmniLuvr]

Its not clear to me what your conclusion is

basically, shadows setup WORKS! but at what cost? higher octane fuel, and a skilled enough tuner to make sure things don't go real bad once your above 3 bar! the second is a biggie!

im basically copying his setup, but hopefully will be able to make some sort of log/? header to move the turbo towards the drivers side a little more.

but since robs "intake" is custom, many might not have the same result, or because rob ported his own head (I think) then people again may not have the same result. same also goes for the stock ported log header...

the reason robs setup works so good is because it is "matched", the parts he chose, and chose to do the way he did work well with eachother.

1. holset turbo- they work very well at high pressure ratings, also flow well, has a 4" dump swingvalve, and a small enough turbine/housing that it also spools well.

2. lightly ported head AND combustion chamber(that part is important I believe)- the head will flow better than stock, easier to match ports, don't have to worry bout going into coolant chambers or destroying a $1250 dollar head if something catastrophic fails, and the fact that he has very little removed from the combustion chamber leaves more of a squish/quench area to help prevent detonation

3. modified intake- seriously, its not that crazy actually, he raised the roof, put his own elbow on it, did some port work and made the runners slightly shorter. he could have actually done much more to it, but then it might out flow his head... might...

4. ported exhaust- well, this thing just works, ported big enough the match the flow of the other parts, keeps pressure up to help with spool, but obviously flows enough to make 500 hp.

the big deal is to see what happens when he changes something in his setup next, your intake manifold may change everything? it could make more power at less intake psi, but the drive pressure may remain the same. so he "could" make 5xx hp at 30 psi but still be at his 38 psi drive pressure? then would a header benefit? im sure, and he has already stated that it will help now. id say the time for a header is when you have access to one or can afford it, plain and simple...

[Force Fed Mopar]

I thought he had a well ported head with larger than +1 valves? It is a bathtub head right?

[OmniLuvr]

I thought he had a well ported head with larger than +1 valves? It is a bathtub head right?

pretty sure only +1 valves, yes g-head with a small amount of deshrouding, and the head is ported "well" ( ;) ), but i wouldnt say it was hogged out massive ports, basically what i would call "stage 3"?

[Shadow]

pretty sure only +1 valves, yes g-head with a small amount of deshrouding, and the head is ported "well" ( ;) ), but i wouldnt say it was hogged out massive ports, basically what i would call "stage 3"?

Couldn't have categorized it better myself! :thumb:

[Reaper1]

Its not clear to me what your conclusion is. That someone planning a 500hp build should add the expense, complexity, and reduced reliability of a tubular manifold when theres proof that isnt required? How does that make sense? How is that easier? You dont suddenly reduce the requirement to tune or tweak because you bolt on a tubular header, if anything you need to have an even firmer grip on whats going on and be prepared to do even more trial and error testing to get it to work right. Or at least, the argument could equally be made in that respect until proven otherwise.

In other words all the stuff Rob may or may not have done to the Charger comes with the territory at that power level, I dont think there is enough data to attach it specifically to using a stock exhaust manifold.


the time for a header is when you have access to one or can afford it, plain and simple...
^This!

[acannell]

the time for a header is when you have access to one or can afford it, plain and simple... ^This!

^This!

But does that strategy realistically help anyone? You could say that about pretty much any upgrade. When people are planning builds there are constraints of time and money and decisions have to be made. I guess what Im looking for is the justification to spend the time/money on a tubular header when you could be spending it on many other more critical things, for an engine build in the 500hp region. Its a chunk of change and is not without its risks and additional work.

If tubular headers were $150 there wouldnt really be a discussion. But they are more like twice that at least arent they? I think onerippinturbo2 is making some nice looking ones in that price range IIRC. I suppose the price for an entry-level tubular header that qualifies as significantly above-and-beyond a ported stocker would be a good number to know in this discussion.

Im not saying people cant come up with any reason to justify anything they want to do with their cars, and my hat is off to them. Its all for fun anyways. But I would like to see the price-of-entry for 500hp get forced down and down and down as much as possible for our cars. And it seems like Shadow has provided us with a great example in that specific regard, by eliminating the cost of a tubular header.

In the same way that, thankfully, the following things are apparently not needed for 500hp: billet connecting rods, $1500 cnc ported heads, 9,000rpm, 60psi, 0.6" lift etc...the more things we can get on the list of "not needed" for a power level that is "very high" the better IMO. I think its reasonable to say a majority of TD/TM'rs will have more fun if that bar gets lower and lower and lower.

[Shadow]

A Proper tubular header would be more in the 800.00-1500.00 range, depending on turbo location ;)

[Force Fed Mopar]

A Proper tubular header would be more in the 800.00-1500.00 range, depending on turbo location ;)

That's kinda what I was thinking also.

There's really no way to make a "one size fits all" header that will work properly. There would have to be at least 2 different ones I think, one for stock to mild builds, and one for full race builds with large ports, valves, intakes etc.

[Shadow]

That's kinda what I was thinking also.

There's really no way to make a "one size fits all" header that will work properly. There would have to be at least 2 different ones I think, one for stock to mild builds, and one for full race builds with large ports, valves, intakes etc.

I think you Could build a "one size fits all", but it would have to be the "all out" version and 1200.00. Remember, Warren's header Keeps the stock location ;)

[Force Fed Mopar]

Hmm, yeah possibly. I guess the exhaust ports really don't increase in size much, (excluding Warren's maybe lol) so primary size requirements wouldn't be much different. That's mainly what I was thinking about. That and the length of them.

[acannell]

Something I have sort of forgotten, but am now remembering, is that I long ago abandoned the idea of making a tubular header product. Or at the very least its below the priority of a) intake manifold and b) swingvalve products, and then perhaps below c) electronics things to log data more efficiently and completely. I kind of wish it was high up on the priority list since it would be a fun product to work on, but I just dont see it as a roadblock to most people since Shadow has been able to get so far with the stock one.

Still, I'm faced with tantalizing possibilities as far as coming up with a tubular header, because of several special factors:

-I already have a tubular, near-equal length header with ~14" primaries, that is stock location, and has survived 1000's of miles. It has too much hand-fitment and not-quite-square-cut angles to copy directly, but I could use it as a guide for how the tubes need to be for stock-fitment, so that HUGE amount of trial-and-error work is done.

-Now that I know how to/and have machinery to CNC cut tubing to precision angles, I could drastically cut down on the labor and therefore the price of a complex header with lots of curvature.

-And also since I have alot more equipment and knowledge than last time around, I could make more complex fixtures to make assembly and welding much easier.

-Ive already figured out solutions for the starter and power steering pump fitment/heat shielding issues

But I just dont see how I can say "you need this and should buy this" to anyone...including myself! For all I know longer primaries reduce exhaust energy enough to hurt turbo performance below certain power levels??? Maybe a tubular header with long primaries is worse than a short header that is more similar to the stock header but just bigger? I dont know.

[Force Fed Mopar]

The way I see it, the header is something that people interested in optimizing a setup are going to want. Whether a street setup with a stock or mild turbo, head etc, or a race setup needing the quickest spool at a required power level, a tube header can eek out that last little bit.

If you just want to make 400 whp and don't care how, then the header is not essential.

[GLHNSLHT2]

In the same way that, thankfully, the following things are apparently not needed for 500hp: billet connecting rods, $1500 cnc ported heads, 9,000rpm, 60psi, 0.6" lift etc...the more things we can get on the list of "not needed" for a power level that is "very high" the better IMO. I think its reasonable to say a majority of TD/TM'rs will have more fun if that bar gets lower and lower and lower.


I got billet connecting rods to be able to get them in a longer than stock length besides saving weight while doing so. Are they needed to make 500hp? No probably not. But the better rod ratio and lighter weight excite me. I really want to build a turbo 8v tall deck next with long billet rods. I love an engine that revs up 2grand with just the tiniest blip of the throttle.

[Shadow]

I'm in the process of building a couple 4-500WHP 8v's right now and I can tell you I'm Not using stock rods in either of them!

Just because the Charger is alive with stock rods at this power level doesn't guarantee that the next set will go 600WHP! lol

I've got to be close to the limit, if not past it already! I would be comfortable building one of our mtrs for up to 400WHP with stock rods. (maybe 450) Once someone is talking beyond that, I think it's just wise to go with something a little safer. :)

[Force Fed Mopar]

Usually aftermarket forged will not only increase strength but also save some weight. So for the price it's generally a win-win. Especially since reconditioned T2 rods are $200 a set, not counting any polishing, shotpeening, heat or cryo treating etc.