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.

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:


Worst in theory, air has to turn too much negating about half of the plenum volume:

[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?