Variable Intake Manifold

[Jadewombat]

Not a new idea, but haven't seen it done yet on a T1 or T4?? Correct me if I'm wrong.

A good read on the subject: http://www.autozine.org/technical_schoo ... haust.html

I thought about it and initially the idea was duals and a center section. The center section for the longer pathway and duals to act as ITBs for the shorter pathways. That wouldn't be feasable though because both sections have to be in the pathway past whatever TB is used. Meaning if you switch from a center section TB to duals, this necessitates have two additional DBW TBs and at the same time the center section DBW TB would have to close--otherwise you have a ton of air trying to be regulated from three sources at the same time. Probably do-able, but the sudden MAP pressure changes would probably make tuning a nightmare (wouldn't be a smooth transition due to sudden changes in air volume).

What would be easier (in theory), is having a center section and two pathways just past the TB. The two pathways would then be regulated by a DBW butterfly valve in the center section that would open at WOT or high-rpms. In this way, the volume of air is not being changed but the speed would be, making it easier to monitor and tune, correct? The center section, I tried to draw it as best as possible (I know, I know--SketchUp is in my future) of the pathways in the attached. Thoughts?

Probably not gobs of power to be made (3-5% increase is the norm.) but should improve the driveability and make things more fun stomping on it. It should feel like having two different engines (or at least sound like it with that growl in the intake).

[andy198712]

theory is there, but how effective it'll be i don't know? BMW played with that did they not??

[gtmdriver]

I think the normal approach is to use variable intake trumpets, or at least it used to be, but I would think that the effect would be very small on an engine with such a small rpm range.

[Jadewombat]

theory is there, but how effective it'll be i don't know? BMW played with that did they not??

Yeah, it mentions that in the link above. They used a variable vane thingy in the middle of their manifold that would change the pathway (and in turn distance) the air would take depending upon how the center section was rotated. A lot of the manufacturers still play with it though, even in the post-direct injection world of engine management.

by gtmdriver » Sun Sep 11, 2016 5:52 pm
I think the normal approach is to use variable intake trumpets, or at least it used to be, but I would think that the effect would be very small on an engine with such a small rpm range.

I agree. There's not a lot of room to play with there. If the bottom of the TB is 4-5 inches to the base of the manifold before it "t"s off to each cylinder bank, then the alternate (longer) pathway for the "u" shaped piece would have to be at least double, 9-10 inches to be a noticeable change in distance.

Let's say it only adds 1-2hp. It'd still be worth it to me to play with one day.