2.4L intake runner length discussion

[BadAssPerformance]

2.4L intake starter kit here.

Long Runner manifold or Short Runner manifold. Which is better and why?

[cordes]

From a pragmatic standpoint, the shorter runners might be beneficial to someone with limited space.

[BadAssPerformance]

True, depending on where you need the space. If a large plenum is added on the end of those short runners is ends up being further from the front of the head than the long runner plenum would be. Could make those runners really short tho...

[TonaChris]

Im no pro, but from what I understand the question seems too broad. It depends what your set up is like and where in the rpm range you want it to be most efficient.

[BadAssPerformance]

It is meant to be a VERY broad discussion type question.

Why would you want them short? or Why would you want them long? ...only commonality being both would be for a 2.4L turbo motor.

[TurboGLH]

With the stock stratus intake (long runner), the low rpm torque is great but power above 5k is poor. Since the head is obviously not the problem, the power band seems to be affected a good deal by the runner length and the plenum volume.

I personally think a 2.4 has enough stroke to make more than enough torque without help. The stock srt intake has short runners and a moderate sized plenum and on the stock turbo with minimal mods my car made 250+ ft/lb from 2600-5500rpm and 300+ from 3000-5000rpm with no effect on hp to redline (at least none that can't be attributed to the boost fall off)

Short runners, big plenum is the way I'd go.

[Frank]

If you are N/A, Short vs Long is a easier topic and more cut and dry. For turbo charged cars, these effects are dampened. However with turbo cars, shorter runners appear to reduce spool time and in addition, they appear to reduce the psi required for x horsepower.

Idealy, you would want shorter runners that taper to a nice fat inlet at the plenum. Yes a big plenum is ideal. However if you go to big, throttle response is going to suck and streetability will fall off requiring you to shrink the throttle body which in turn screws up your turbo efficiency again. I would target a plenum displacement of 1.5 x engine displacement and go for a 65mm throttle body.

[cordes]

Frank, could you elaborate on the theory behind shorter runners requiring less boost to make a given HP? Moreover, would a well thought out 8v setup benefit from this, or would it really only apply to a nicely done 16v setup?

[Frank]

To elaborate... if the pressure differential is decreased between the turbo and the valve, then your turbo runs at in a more efficent area of the map. When this happens, temperature decreases. When temperature decreases, you have more air density and more power. When less pressure is required for x hp, then throttle response also increases even if you have less torque then before due to the short runners.


Frank

[8valves]

Frank, could you elaborate on the theory behind shorter runners requiring less boost to make a given HP? Moreover, would a well thought out 8v setup benefit from this, or would it really only apply to a nicely done 16v setup?

If you remember from last year, my intake mods made a HUGE difference with the car. It was truly a bottleneck so to speak, and should be even better this year.

Agreed on either a 2.2/2.5/2.4 making enough bottom end all on it's own.

[Skibbe]

This is an interesting read:
http://www.amsperformance.com/pdfs/intakemani.pdf

I like the idea of the raised stacks inside the plenum that catch smooth air toward the center rather than stagnant air around the outside.

JT, maybe we'll have to play with cutting an air horn plate on my mill.

[8valves]

This is an interesting read:
http://www.amsperformance.com/pdfs/intakemani.pdf

I like the idea of the raised stacks inside the plenum that catch smooth air toward the center rather than stagnant air around the outside.

JT, maybe we'll have to play with cutting an air horn plate on my mill.

Check a thread I just put up in the intake section for that plate!

[cordes]

Someone posted a link to a site which sells the cones amongst other things for a very reasonable price. I think it might be in the fab section, but I am not sure.

[BadAssPerformance]

This is an interesting read:
http://www.amsperformance.com/pdfs/intakemani.pdf

I like the idea of the raised stacks inside the plenum that catch smooth air toward the center rather than stagnant air around the outside.

JT, maybe we'll have to play with cutting an air horn plate on my mill.

I have access to a CNC at work... ;)

[Skibbe]

I have access to a CNC at work... ;)

And I have access to CNC in my basement. :thumb:

Though yours is probably a bigger machine. What do you guys use for generating toolpaths?

[BadAssPerformance]

Solidworks for CAD then Strategist for code.

[Skibbe]

I just checked out Aaron's other thread. I was looking at the sheet metal velocity stacks he made, and it hit me that this has to be similar to culvert design, which is what I happen to be doing at work.

The absolute worse culvert to have, as far as entrance losses go, is a sharp edged protruding inlet. I was just working with a corrugated metal pipe set up like this and in theory this would be the same for the sheet metal velocity stacks.

So that go me thinking about the AMS theory also. They're worried about grabbing stagnant air at the bottom of the manifold. But really, by machining that plate, they are just moving the floor up farther, and thus moving the stagnant air higher. The velocity on any surface is going to be zero, no matter where that surface is.

Just for giggles, since I have it handy... here are the Ke (coefficients of entrance loss) for some culverts, taken from the Civil Engineer's Handbook:

Sharp-edged projecting inlet....................0.9 (similar to sheet metal stacks)
Flush inlet, square edge..........................0.5 (similar to drilling a hole for the pipe and inserting)
Concrete Pipe, groove or bell projecting.....0.15 (similar to the sheet metal stacks, but making it really thick pipe)
Concrete pipe, groove or bell flush............0.10 (chamfered entrance, flush pipe)
Well rounded flush entrance.....................0.08 (A radiused entrance, flush with the bottom of chamber.)

So, in theory, Aaron's radius flat plate is the best, followed by AMS's protruding plate, with the worst being the sheet metal velocity stacks.

[Skibbe]

Pictures from Aaron's post to go with above...

Best in theory, larger the radius the better on the entries:
http://www.turbo-mopar.com/forums/photopost/data/500/medium/DSCF0038.JPG

Worst in theory, air has to turn too much negating about half of the plenum volume:
http://www.turbo-mopar.com/forums/photopost/data/500/medium/DSCF00181.JPG

[cordes]

Did you check out the link that the posted to the article about the velocity stacks?

[Skibbe]

Did you check out the link that the posted to the article about the velocity stacks?

The AMS article I posted? Or a different one?

[BadAssPerformance]

Good info Mike. Thought on the stacks... aerodynamics are a little different that hydrodynamics which are heavily dependany upon gravity during flow.

[cordes]

The AMS article I posted? Or a different one?

yeah, actually it was the one you posted. I did not realize that. Anywho the different taper and the airhorns made a pretty big difference in power over the radius entry manifold.

[Directconnection]

Frank, could you elaborate on the theory behind shorter runners requiring less boost to make a given HP? Moreover, would a well thought out 8v setup benefit from this, or would it really only apply to a nicely done 16v setup?


Shorter runners like we are seeing made for our cars are designed for really high rpm peak power. Our cars don't really make high rpm peak power besides a few select individuals. I read a little bit on intake tuning and runner length and from what I gather, these super short runners are not matched for our cars at all. I am quite sure most people that make these for their cars are not crunching the #s and formulas involved, but rather just going at it from a packaging standpoint and gathering that short runners are better for HP (which they can be if designed properly).

But why are they working? I think one reason they are working well for some is that the short runner has minimal flow losses on the head. Yes, it's just a tube with no valve, so it should flow like 99% efficient, but that is not the case. My stock 2-piece bottom half of the intake only.... showed a 29 cfm loss bolting it to a head. I increased the volume considerably and flow loss reduced to 13 cfm.

In summarry... these short runner intakes most likely are not tuned to a
2.2's peak power #s but the hp increases are more due in part to a very minimal flow loss.

That's my take from some things I have picked up upon.

[Directconnection]

I am doing heavy radius entry on my 2-piece plenum. just scared to cut it open;)

Alot of welding is going to be added to this puppy.

[BadAssPerformance]

Shorter runners like we are seeing made for our cars are designed for really high rpm peak power. .

So for a 2.4L, how short and how high of RPM for big HP?

[Skibbe]

Good info Mike. Thought on the stacks... aerodynamics are a little different that hydrodynamics which are heavily dependany upon gravity during flow.

I don't know what dependany means, but yes, there are sure to be differences in flow between water and air. However, the entrance losses have got to be similar, as both involve fluid flow through an orifice, which is all I was looking at.

More research is definitely in order. Need to take off the Civil hat and find out where I left my Mechanical Engineer hat...

[BadAssPerformance]

LOL, dependany = depandant ... I kant tyep or speel!

[Frank]

So for a 2.4L, how short and how high of RPM for big HP?

Go by the seat of your pants... that is all you can do.... formulas don't work too well on boost situations. You can go with the rule of thumb for the plenum listed above for streatable. If you want massive power, go with a 4.5 liter plenum and a 3" inlet and 75mm throttle body.


Frank

[8valves]

I just checked out Aaron's other thread. I was looking at the sheet metal velocity stacks he made, and it hit me that this has to be similar to culvert design, which is what I happen to be doing at work.

The absolute worse culvert to have, as far as entrance losses go, is a sharp edged protruding inlet. I was just working with a corrugated metal pipe set up like this and in theory this would be the same for the sheet metal velocity stacks.

So that go me thinking about the AMS theory also. They're worried about grabbing stagnant air at the bottom of the manifold. But really, by machining that plate, they are just moving the floor up farther, and thus moving the stagnant air higher. The velocity on any surface is going to be zero, no matter where that surface is.

Just for giggles, since I have it handy... here are the Ke (coefficients of entrance loss) for some culverts, taken from the Civil Engineer's Handbook:

Sharp-edged projecting inlet....................0.9 (similar to sheet metal stacks)
Flush inlet, square edge..........................0.5 (similar to drilling a hole for the pipe and inserting)
Concrete Pipe, groove or bell projecting.....0.15 (similar to the sheet metal stacks, but making it really thick pipe)
Concrete pipe, groove or bell flush............0.10 (chamfered entrance, flush pipe)
Well rounded flush entrance.....................0.08 (A radiused entrance, flush with the bottom of chamber.)

So, in theory, Aaron's radius flat plate is the best, followed by AMS's protruding plate, with the worst being the sheet metal velocity stacks.

Very interesting stuff indeed! It makes me curious for sure. The protruding stacks are the rage and are on the fastest small displacement forced induction cars out there as far as I've seen. Makes you wonder for sure.

[Skibbe]

Very interesting stuff indeed! It makes me curious for sure. The protruding stacks are the rage and are on the fastest small displacement forced induction cars out there as far as I've seen. Makes you wonder for sure.

I'm curious too. Any pictures you can link to of the others?

[NeonShowCar]

Go by the seat of your pants... that is all you can do.... formulas don't work too well on boost situations. You can go with the rule of thumb for the plenum listed above for streatable. If you want massive power, go with a 4.5 liter plenum and a 3" inlet and 75mm throttle body.
Frank

Your correct the formulas dont' work very accurately, that's why you need to start using a CFD analysis program. There's gotta be someone out there that's a CFD user - that could model an intake manifold and change plenum volumes / runner lengths.

The tools are out there to stop all of this guess work, just need to find someones an expert in CFD analysis that could run different simulations overnight and have results the next day. When I was developing intake manifold, used to have a CFD engineer that would run different configurations and give us the result.

If anyone is able to find someone who is an expert with CFD, you could have all of your questions answered very easily - then the person would have to be willing to share the information. And not hoard it like the old days!

[Directconnection]

Go by the seat of your pants... that is all you can do.... formulas don't work too well on boost situations.

Frank

Why not? Chrysler engineers did it! :)

Also, do you really think boost affects the pressure wave in terms of ft/sec? If not, then a tuned runner should be the same for both applications. If it does affect the pressure wave in terms of distance in time, then it must vary for N/A as well, as velocity must affect it's speed.

[glhs875]

I'm still testing and learning, although at a standstill for the moment, but I'm finding that cross sectional area has a larger effect on the power band than the length of the runner in boosted form. I used to have a T1 log car that I modified and it still had tons of low and midrange torque with almost no runner length. I've yet to try out the highly ported lower on my 2 piece intake where I enlarged the cross sectional area alot. But I'm expecting some big gains in the mid to upper R's (5K to 7K+) with the length remaining the same as before. Once boost is made, that overshadows an intake somewhat that has runners that are too short to make good torque in NA form. But if the cross sectional area of the runners is only large enough to support say 5500rpm for a certain size of engine, than that's pretty much what will happen even in boosted form but with the R's extended slightly. I feel more of a difference in throttle/boost response and low to mid range torque output will weigh more on the intake/cam as larger and larger turbos are used that won't spoolup as low in the rpm range. The smaller turbos can cover up missmatched combos in the low/midrange area. When I pick a turbo, I think of it like I would when picking a camshaft. And when it comes to the intake setup, the more and more I can reduce the restiction all the way to the valve area of the head the better. Boost made is from a restiction somewhere, and the closer the restriction causing the boost to be made is to the intake valve, the better the intake will perform in the upper R's. I feel cross sectional area will reduce the restriction towards the valve more than length. But both should still be considered. A turbo for the most part merely amplifies with torque increases the natural power band of the engine. With small turbos able to shift the power to the lower R's and larger turbo's to the higher R's somewhat. I may change my way of thinking, but for right now I base my intake both length and cross sectional area to perform it's best in the peak power RPM area based from NA principles for a street strip combo. I have found from ET'ing my car that it takes a ton more HP and RPM's to overcome a large torque output reduction. That high midrange torque output is needed for good ET's at least in a street strip setup. On my own car I have found that it would take shifting the peak power and shift points to around 7500rpm to actually ET better than shifting at 6200 to 6400 rpm. When experimenting, my ET and MPH was virtually identical shifting at 6400rpm and getting into high (3rd) gear vs. keeping it in 2nd gear and crossing the line at around 7100rpm in the 1/8th. The greatest point of acceleration occurs at the peak torque range. And designing the induction setup to have peak torque in rpm range you are running in while going down the track will yield the best results.

[Directconnection]

You know what? I was reading on dave vizard's site years ago... and he had a basic rule of thumb for runner length. It was a simple formula...not scientiffic as it was just to give people an idea of a general length. The 2 piece bottom half came out right to the tune of somewhere's around 5,500 rpms...give or take a few 100 rpms. For me with a 2.5 that isn't going to make peak power over 6k, I think I have the perfect, factory engineered tuned runner length already. The 1-piece has shorter runners, so maybe a better choice for 6,000+

[BadAssPerformance]

Go by the seat of your pants... that is all you can do.... formulas don't work too well on boost situations. You can go with the rule of thumb for the plenum listed above for streatable. If you want massive power, go with a 4.5 liter plenum and a 3" inlet and 75mm throttle body.


Frank

6" runners sound good with that?

[turboshad]

Don't forget, runner length is all the way to the valve. When I was at unniversity we did testing with a variable runner length/variable plenum volume intake on a yamaha R6 engine converted to fuel injection. We also did tests with a varaible lenth equal length header. Out of all the changes we made the runner length had the largest impact on the performance curve. Runners change the tuned RPM with the shorter acentuating the higher RPM (shorter wave length = higher frequency) and the longer runners moving the peak down in RPM (longer wave length = lower frequency) Even when we were changing the runner length there was still an obivious characteristic to the engine and how it was set up. It wasn't until our runner length complimented the natural tendencies of that engine that we got our ideal length. This was on an NA engine and involved many dyno-change-dyno-change-dyno...... procedures. The cool part is before we did testing we made a model on a program called GT Power to see how accurate that would be. It turned out that our real life testing and what we found to be the optimal setup matched almost perfectly with what the software told us. Only down side is the program is crazy expensive. I would love to have a copy to play with at home.

When I made my intake for the 2.4 it was mainly designed around packaging but I wanted to keep a shorter runner length since I know this engine will breath better in the higher RPMs than my 8V. The two options I had for packaging either went with short runners and the plenum up high or larger runners curled arond with the plenum lower. Because I wanted the shorter runners I did it that way. The runners them selves ended up being about 5" with about 2.625"-2.75" of runner in the head. This puts them at around 7.75". For the plenum I needed it to clear the alternator and I wanted around 1.5X or slightly larger. In the end it was about 4l wich is just over 1.5X displacement and I used a 3" bend that matched nicely with my 65mm *cough* Ford *cough* TB. I also machined the entrance to each runner with a decent radius (I belive it was 3/8" but can't remeber for sure) and then smoothed it into the runners. Hopefully in a couple months I can tell you how it performs. Here's some pics if you haven't already seen them.

http://i54.photobucket.com/albums/g103/turboshad/93%20Shadow/DSC01472.jpg

http://i54.photobucket.com/albums/g103/turboshad/93%20Shadow/DSC01476.jpg

http://i54.photobucket.com/albums/g103/turboshad/93%20Shadow/DSC01500.jpg

DJ

[Directconnection]

Probably find an out of date bootleg version of that software online somewheres. My old shop had a full version of mastercam that we used for years. It was bootlegged somehow as it was a tutorial version but fully functional in all ways.