Type IV plenum intake manifold questions..., Why single and not double like the 911 motor? Options

[Mueller]

Has anyone made a dual plenum like used on the 911 engines for a Type IV?

[Jake Raby]

When I've gone this way the result was an even more difficult to tune engine that was much more picky about cam specs than any other way. I've always had better luck with twin ITBs over a central plenum or a pair of localized plenums.

Only once has this made more power here and that was a 2.6L engine for a square back where I was able to get 80% of the engine's displacement into a pair of plenums. It wasn't worth the 6Hp that it made.

This post has been edited by Jake Raby: Mar 14 2015, 10:29 PM

[toon1]

When I've gone this way the result was an even more difficult to tune engine that was much more picky about cam specs than any other way. I've always had better luck with twin ITBs over a central plenum or a pair of localized plenums.

Only once has this made more power here and that was a 2.6L engine for a square back where I was able to get 80% of the engine's displacement into a pair of plenums. It wasn't worth the 6Hp that it made.

My plan was to do ITB's with two plenums and longer runners for better low end performance. The trick would be to get the optimum runner length. That would be a lot of dyno time. I would suspect that the engineers designed the length of the stock runners close to optimal for a daily driver.

I don't see much benefit to dual TB,s on a single plenum (for a daily driver). Tip in tuning would be hard to get correct. Progressive, dual TB,s would be kinda neat to try. Have the second TB start opening at say 3K rpm.

Even if you were to stay with a single TB and single plenum. I think there is a lot of room for improvement on the stock system.