Guaging Interest Excessive Manufacturing Intake Plenum GB

[CoopKill]

As I think about it, the shortened runners may be able to be angled some when welded back together to clear with the tank.

[familyMAN]

Let's look at shorter runners.

9" doesn't include the lower mani or head to intake valve. I would do spacer on lower to upper if we have to, to get as short of runners as possible and rear plug access with the bit plenum. (DR mani needs spacer). Angle plenum is a good idea. There is some excess clearance to hood to accommodate.

[CoopKill]

If you want short as possible, then it is possible to stand the tank on end forward. Puts the tb in the valley position. I see no reason it would not be doable other than hood interference, which I would say you need 6-6.5 inches from the lower intake.

[familyMAN]

I don't want short as possible. Want approx 11" from intake valve to plenum. I need to measure to see how much needs to be taken off NA runner.

[CoopKill]

I can do that tomorrow as it is all apart right now.

[familyMAN]

Back from toretto's garage....
intake valve to middle of opening on head ~3"
Lower~4"
NA runners (measuring middle of space) 7.75"
Add ~.25" for the plenum plate that XM adds
Total 15"

Just mounting plenum to lower intake would give only 7" of runner length which I believe is too short for anything other then crazy revs.

I want 11" total so 4" taken off. Would settle for 3"

Can we do it??

[CoopKill]

I think doable. I will have to check on the height of the tank. It is the only thing missing in the sketch.

[NOMIEZVR4]

damn eric...you're making this hard for me...

[familyMAN]

Here are some guesstimates....
8k peak power...11" runner (measured from back of intake valve to start of plenum)
7500 peak...12" runner
7000 peak....12.75" runner

So 11" would be a little short for my turbo and cam setup. 12-13" would be better for my setup (and most others) which should help with packaging also. Especially if a slight angle were added, but not sure what if anything that will do to even cylinder distribution.

Edit: 15" runner should hit peak around 6k. Stock TT runner at ~16.5" would peak at 5400. Hmmmm. Anyone ever see a 3S dyno where horsepower stops climbing around 5500 and flattens instead, even if turbos still have some juice? (obviously rhetorical, we can post dozens of dynos that shows exactly that, regardless of power level) If you have cams already, this should be a requirement IMO.


Disclaimer: Shortening your runners will change your hp "curve". Moving up and right. You will may lose some tq outside of peak power band. Bigger plenum only would be best if you want to pick up some hp everywhere in boost but little to no loss otherwise. Your "curve" shouldn't change. Only move up.

Disclaimer2: I don't have a dizzying amount of math to back the guesstimates up. I do however spend way too much time on multiple turbo forums and can recall entirely too many dyno numbers and modlists. The above is based on some simple correlations.


Are there any back to back comparisons of this mani with the NA runner length on any other cars? turbo or na, doesn't matter.

[J. Fast]

Here are some guesstimates....
8k peak power...11" runner (measured from back of intake valve to start of plenum)
7500 peak...12" runner
7000 peak....12.75" runner

So 11" would be a little short for my turbo and cam setup. 12-13" would be better for my setup (and most others) which should help with packaging also. Especially if a slight angle were added, but not sure what if anything that will do to even cylinder distribution.

Edit: 15" runner should hit peak around 6k. Stock TT runner at ~16.5" would peak at 5400. Hmmmm. Anyone ever see a 3S dyno where horsepower stops climbing around 5500 and flattens instead, even if turbos still have some juice? (obviously rhetorical, we can post dozens of dynos that shows exactly that, regardless of power level) If you have cams already, this should be a requirement IMO.


Disclaimer: Shortening your runners will change your hp "curve". Moving up and right. You will may lose some tq outside of peak power band. Bigger plenum only would be best if you want to pick up some hp everywhere in boost but little to no loss otherwise. Your "curve" shouldn't change. Only move up.

Disclaimer2: I don't have a dizzying amount of math to back the guesstimates up. I do however spend way too much time on multiple turbo forums and can recall entirely too many dyno numbers and modlists. The above is based on some simple correlations.


Are there any back to back comparisons of this mani with the NA runner length on any other cars? turbo or na, doesn't matter.

Excellent post. The group buy guys will be the first to test. My engineers intuition tells me we'll get an rpm shift of 500 for every 1/2" of length change on the runner. We'll soon find out.