Dual wastegates...Lets see if....

[MOPAR2YA]

I plan on trying this at SDAC, if it works it will be a good compromise between a small turbine for good spool and a larger one for peak power.
http://www.turbododge.com/forums/f11...why-u-ask.html

[contraption22]

If backpressure in the manifold was a problem that could be solved with more wastegate flow... wouldn't you have problems with boost creep?

[MOPAR2YA]

Not really. I know Larry J was running well over 2:1 backpressure and he was controlling boost, there is a point where backpressure becomes so severe that the wastegate cannot flow enough to control boost. I dont knw if that is at 2:1 3:1 or where. I know on my T3T4 that the stock internal gate could not hold without haveing 3 external spings pulling the flapper closed. Id love to have known what the back pressure was.

[contraption22]

So why don't the the pros use one wastegate per cylinder and tiny turbines with huge compressors to make quick spooling, high flow turbos?

[tryingbe]

Pro doesn't need it to be a daily driver?

[contraption22]

What I am trying to say is that it is likely that you will have the same exhaust pressure no matter how much wastegate flow you have, because the same amount of exhaust energy is going to be needed to maintain the desired boost pressure. If the wastegate you had been using wasn't flowing enough to keep backpressure under control, you would have boost creep. The amount of work the turbocharger has to do determines the backpressure, not how big the wastegate hole is... because the wastegate is going to stay closed until the desired boost pressure is reached, once below that boost pressure, its going to close again.

If it worked, somebody else would be doing it by now... don't ya think?

[Ondonti]

Or he could be depending on exhaust gas velocity keeping the turbo spooled even though there is less pressure in the manifold.
High pressure in the manifold helps initial turbo spool but then instantly starts to hurt spoolup and power.
But then how do you prevent all that velocity/power from just going out the wastegates...or will there still be enough energy going to the turbine to maintain boost pressure. Will less reversion also help keep the turbine spooled up...

I understand the boost creep idea but

High pressure in the exhaust manifold kills the velocity of the exhaust gases. Dumping some of that pressure would cause the whole exhaust system before the turbo to behave differently so you cant just assume that you will lose the ability to keep the turbo spooled up.

If the exhaust manifold was a wastegate biased design then I could see this being a problem with "too much" wastegate. On that note I think a lot of very successful turbo manifolds used in professional racing of years past have had wastegate biased manifolds (flow to wastegate being more important then flow to turbine) so this might be a similar function as running two wastegates.

my thoughts.

[contraption22]

Or he could be depending on exhaust gas velocity keeping the turbo spooled even though there is less pressure in the manifold.
High pressure in the manifold helps initial turbo spool but then instantly starts to hurt spoolup and power.
But then how do you prevent all that velocity/power from just going out the wastegates...or will there still be enough energy going to the turbine to maintain boost pressure. Will less reversion also help keep the turbine spooled up...

my thoughts.

You're putting way too much thought into this and ignoring the simple function of a wastegate. A wastegate is not going to work differently just because it is willed to.

If Wallace's turbo needs 30psi of backpressure to make 15psi of boost... then he is still going to have 30psi of backpressure at 15psi of boost even with two wastegates.

[Dave]

I see where Wallace is coming from. At 15psi it may be around 25% of the exhaust flow opposed to 25psi. Once he hits 25psi there still will be excess exhaust pressure, that pressure then needs to go somewhere. He's not concerned with the flow rate and efficiency of the turbine housing so much as he is of getting everything out as fast as possible. It takes only so much work to produce 25psi, after that the engine is still producing more exhaust pressure than what it was at 25psi. Instead of stacking the exhaust pressure he seems to be taking that wastful backpressure and dumping it out. In a turbo system it's like taking advantage of wasteful energy... twice.

Sounds complicated but in theory it should work.

[Ondonti]

sorry I added more when you typed this, but as I said earlier

I think the existence of wastegate biased turbo manifolds would say that the function of a wastegate can be more then just boost control.

You can keep a turbo spooled up without having high pressure in the turbine manifold.
The idea is to maximise velocity to the turbine to keep the turbine spooled and minimize pressure in the manifold. Thats how you make huge power.

[Tony Hanna]

So why don't the the pros use one wastegate per cylinder and tiny turbines with huge compressors to make quick spooling, high flow turbos?

Just a guess, but the ammount of energy transfered from the exhaust side of the turbo to the compressor side has got to be equal less friction loss. I would imagine that with the small turbines (and housings) the backpressure would have to be high in order to transfer enough energy to keep the compressor building boost.
Basically what I'm getting at is that by the time you dump enough exhaust with the wastegates to reduce backpressure any reasonable ammount, you're no longer going to have enough energy to drive the compressor.
I may be wrong though...

Edit: you already said that and somehow I overlooked it.

[Dave]

You can keep a turbo spooled up without having high pressure in the turbine manifold.

Only if the amount of exhaust pressure does not exceed what the volume and efficiency of the turbine housing can handle. Past that point it becomes, proclaimed, inefficient.

[Ondonti]

Only if the amount of exhaust pressure does not exceed what the volume and efficiency of the turbine housing can handle. Past that point it becomes, proclaimed, inefficient.

What does this have to do with my comment? You are talking about the limitations of a turbine housing and I am talking about the fact that high exhaust manifold pressure is not what is needed to keep a turbo spooled.
My example does not talk about the limits of the turbine housing since the purpose of the dual wastegates is to ignore the limites of the turbine housing and simply concentrate on making sure the turbine blades still spin fast enough so that boost does not drop off.
Exhaust gas velocity is much more important in making big power and keeping the turbo spooled then pressure in the manifolds. Pressure kills velocity and causes reversion.
If wallace can decrease exhaust manifold pressure and prevent boost from dropping he should have a huge increase in HP at the same boost level and be able to successfully use more aggressive cams etc. .

[Dave]

What does this have to do with my comment? You are talking about the limitations of a turbine housing and I am talking about the fact that high exhaust manifold pressure is not what is needed to keep a turbo spooled.
My example does not talk about the limits of the turbine housing since the purpose of the dual wastegates is to ignore the limites of the turbine housing and simply concentrate on making sure the turbine blades still spin fast enough so that boost does not drop off.
Exhaust gas velocity is much more important in making big power and keeping the turbo spooled then pressure in the manifolds. Pressure kills velocity and causes reversion.
If wallace can decrease exhaust manifold pressure and prevent boost from dropping he should have a huge increase in HP at the same boost level and be able to successfully use more aggressive cams etc. .

Sorry I thought you were referring to the turbine housing, not exhaust manifold. My mistake, should've read better.

It is, however, still an issue with what Wallace plans to be doing. I see what Contraption is saying, if you loose too much of that pressure there will be less velocity. But what's the say you will have too much or too little pressure because of the extra wastegate? I think that will ultimately depend on head flow and cam lift/duration.

[GLHSKEN]

It will be interesting to see the results. Thanks for sharing

[MOPAR2YA]

Back pressure has litle to do with turbine speed. Stephane was running just under .98:1 with 38 psi intake pressure if I recall Larry J was well over 2:1 with 25 psi intake pressure. Think of accelerating a car, it takes alot of power to get it to 70 mph, but once its there it requires alot less to maintain that speed.

This is a good read...http://en.wikipedia.org/wiki/Variabl...y_turbocharger
http://www.autozine.org/technical_sc...h_engine_3.htm

If it doesnt work, I will have a wastgate for sale and a block off plate to install, but Im confident it will work.

[8valves]

I think the existence of wastegate biased turbo manifolds would say that the function of a wastegate can be more then just boost control.

DING DING DING!

That's why real well though out manifolds don't pull 90* from the turbine housing or collector in fron to fit... they pull smoothly from the area entering the turbine. Even better yet, in theory, is the turbine entry tube that drops down into the turbine housing and the straight section goes into a MONSTER wastegate.

Then by using the small AR housing the spool comes on faster but doesn't choke up top.

However, we thought about doing this a while back and came up to the point that it might only help (as far as using the small AR with the big wastegates and a prioritized header design) if your car has the means to hook up the powerband lower in the RPMs. In our cars cases we decided probably not.

I'll be curious to see how it does pulling from that particular location.

Good thought, hope it works!

[The Pope]

an example of much of this thread is as simple as looking at an SRT 4 turbine and how they get over 300 WHP from a straw size turbo. Most internal wastegates are located at the turbine, which means on a factory style intake you get big reversion and you hurt flow into the turbine by making the exhaust turbulent and changing directions in the scroll. The SRT 4 uses a huge wastegate, not much different than 2 little ones. But much more important it releases the huge exhaust back pressure in the center or the manifold, not one end. Then the tiny turbo doesn't have a valve in its scroll to hurt the smooth flow of exhaust to the wheel. So it isn't the direct need for more wastegate, it is a need for one big one in the right spot to ballence the exhaust for more power, spool up, etc.

[MOPAR2YA]

I suppose I will find out at SDAC. This may not be the most optimal setup, but its gotta be better than what I had.

[turbovanman²]

Interesting, going to nice to see what happens.