I want this plenum... anyone know who made it?

[familyMAN]

To keep the discussion going with a narcissistic quote of myself from the GI thread (more appropriate here anyway)...

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.

To add to that......
back of intake valve to lower plenum is ~3"
Lower plenum is ~4"

Mounting directly to lower plenum, even with an inch extension only gets 8" runner length and could be a quite high peak hp rpm. I hope to have the time, skill and coin to build two mani's to test: one zesty style, one xm/dr style but shorter runner length. Both targeting around 3-3.5l plenum volume and both to use a Q45 TB. Don't hold your breath, will take me awhile.......

[fastfalcon94]

I'm trying to make sense of some of these numbers to figure out what would be best for my dr750s. Something doesn't seem right. FamilyMan you mentioned "Stock TT runner at ~16.5" would peak at 5400." Based on other measurements posted in this thread though, wouldn't it be 18" for a stock TT manifold?

back of intake valve to lower plenum is ~3"
Lower plenum is ~4"
TT runner = 11"
NA runner = 9"

Regardless I know my runner needs to be a little shorter so maybe just by using the NA runner with the XM tank it would be perfect. That would be 16". Any guesstimates on peak here?

[familyMAN]

I'll have to look at the runners again. I have both TT and NA in garage.

16" in theory would be around 5500-6k. About the same as stock but bigger plenum and TB should increase HP.

Intake mani testing doesn't always match theory. Found a huge NA intake test including moderate to wild cams and a short 4.5" runner (plus head to intake valve) so about like a zesty for us started leveling off at 9k. Made 40hp over stock. 150 to 190hp. Of course it dropped off down low a lot. Adding wild cams (much wilder duration then anything we have) gained only a few hp.

That's why I am excited to see virtual dyno more widely used. The more back to back we can do the better info we will have. It's all a MAJOR guessing until someone try's it td04, td05 and bigger.

The supra chart I posted had about 7" total length to valve and it made great improvements above 6k on stock cams, but it wasn't turbo limited like most td04 setups. I have no idea how a high back pressure setup will work. Maybe like NA, maybe not.

Everyone has been saying you need plenum volume for high hp but then I look at Nelson's and it may be only as much as stock and he is rockin major hp.....

We need testing!!!!

Good news, I don't think the XM will hurt. Risk vs reward should be in favor of reward

[familyMAN]

Also, the XM mani does use NA runners but adds a big spacer so it ends up having runner length almost like a stock TT.

[fastfalcon94]

Is the spacer there so it clears the rear valve cover? I didn't remember reading about one in the XM group buy.

Also this one doesn't look very efficient as it's a box design and not curved, but the guy has been dropping the price down on ebay for the past few weeks.

Aluminum Race Intake Manifold Dodge Stealth Mitsubishi 3000gt | eBay

[familyMAN]

Spacer (thick mounting flange) is between upper runners and plenum.

[sergechronos]

The supra chart I posted had about 7" total length to valve and it made great improvements above 6k on stock cams, but it wasn't turbo limited like most td04 setups. I have no idea how a high back pressure setup will work. Maybe like NA, maybe not.

Everyone has been saying you need plenum volume for high hp but then I look at Nelson's and it may be only as much as stock and he is rockin major hp.....

We need testing!!!!

Good news, I don't think the XM will hurt. Risk vs reward should be in favor of reward

With FI, a lot of issues are covered up within the intake system design but the basic rules should still apply. With one of those plates to measure back pressure plus VD, should be pretty easy to get solid information though regarding swaps. Would be great if we could get several intakes shipped to a group that has several different cars (stock, upgraded TD04, TD05, stroker, etc.) all within a small area to swap them around and record data on a day to get a rough approximation, but probably unlikely to get vendors (or even members) to ship off manifolds for that kind of testing.

Volume of the manifold should only need to be around the displacement of the motor, beyond that probably ends up with diminishing returns on performance and you are definitely going to get poor throttle response at lower RPMs. I would venture that a larger plenum would be beneficial even for TD04 guys, changing runner lengths on the other hand may not be. Emphasizing top end and moving the powerband to the right a thousand RPM or so MAY be of use but how much of a difference it would be and how it would change drivability, couldn't say.

TD05 and T3/T4 guys probably stand to gain the most from different runner lengths for the strip, although actual street usage may vary. Moving it right to emphasize their power band would definitely net improvements to peak HP and TQ, although may cause slower spool and off-boost response to make it more obnoxious to drive on the street or cruise on the interstate.

Maybe we could get vendors to bring/ship intakes to go to NG or something and mix them around a bit to see what happens? Would be worth it to get solid definite numbers, or even to find out that maybe they actually make it worse except on the track. Valuable info to be had for sure.

[sergechronos]

Is the spacer there so it clears the rear valve cover? I didn't remember reading about one in the XM group buy.

Also this one doesn't look very efficient as it's a box design and not curved, but the guy has been dropping the price down on ebay for the past few weeks.

Aluminum Race Intake Manifold Dodge Stealth Mitsubishi 3000gt | eBay

It's an aluminum tank, shouldn't take too much to modify it. The not-squared off corners likely help air distribution though to make sure all 6 runners get a good and fairly equal amount of air. Would prefer to see more of a rounded kind of < shape to it to move air better, but at that price, doesn't look too terrible. Would be worth putting it on a VD at least

[NOMIEZVR4]

TB, Throttle Cable, and IC piping accommodations would also have to be considered. Swapping Plenums will change the locations of all those things. I'm all for providing before/after data.

Also the cars on which the parts are being tested should be pushing their setups..not pumpgas on 15lbs boost...lol

[sergechronos]

That's a given, but most of the available upgrades like the XM, DR or that eBay one should be close enough to stock to keep the TB, cable and IC piping . Anybody considering upgrading the intake likely has little to no problem with altering those sorts of things. and outside of IC piping modifications, the throttle cable and TB changes likely could just be swapped from vehicle to vehicle during the tests without too much trouble. Still less work to do that than it is to swap from 9Bs to upgraded TD04s to TD05 to T3/T4. Somebody make this happen!