Tjabo

Hello everyone,

I've been searching pretty hard on here, and I'm having a hard time finding any thoughts on what board members are feeling about intake plenums for forced induction applications. To me it looks like 2.5 liters of plenum size OR MORE per liter of engine displacement might not be out of line. . .

I see Magnus advertises 5 liters of plenum size on their Evo manifold, and the sweet Wilson one Miller is running looks like it might be even bigger than that.

Any thoughts are appreciated!

Tjabo

After doing marathon searching on the internet yesterday, the magic number for a basic formula in general seems to be 1.25x engine displacement to 1.5x engine displacement. The higher volume to bias the powerband toward the upper end as I would like to do.

The thing is, these general numbers have probably been developed more for engines of significantly larger displacement than our four-bangers, AND the "top end" biased power band might still be for much lower RPMs than the power bands that are common on this board. For my part, I'm not looking to rev any higher than 9k ever probably, and for now my rev limit is more like 8,500.

Anyone have any thoughts on what would be an appropriate plenum volume with those factors in mind?

Thanks in advance for your thoughts!

intense4thgen

ive been lookin into the same issue and ive decided for my self to go with 3 liters of displacement in the plenum on my b20/vtec. Having looked at the magnus and compared it to the victor x my thought is that its to big for a street car set up of around 450whp. keep in mind this is just my 2 cents.

92TypeR

There is no optimal size or equation, as there are too many variables that influence the required size.

However, a good general rule is 'bigger is better'. At some point throttle response begins to suffer, and that is a good stopping point.

I don't think FI applications need to be concerne too much with plenum size and runner length, as the turbine itself has larger influences peak power, peak engine speed, etc.

scmil95eg

1.5 x displacement is what I hear a lot as well, but I think what 92TypeR said is spot on, too many variables for there to be a one-size-fits-all formula. This is the reason we came up with a user adjustable piece (but I'm not going to get into advertising here).

Please don't take my rebuttal the wrong way - I think you provide some of the most accurate information on this site and save me from posting quite often. But, frequency tuning has the same effect on an engine, regardless of manifold pressure.

We learned this first hand when we supplied the intakes for the turbo Buick Indy cars (mid-eighties), and did lots of development work and testing. More recently, we worked with an OEM on a LeMans version of one of their production cars. Their engineers were of the same mindset you described above. So, they agreed to try one manifold 'their' way vs. one manifold 'our' way. Let's just say the rest of the manifolds were supplied 'our' way. I'm not exactly sure what you'll find, but look into the last years of the S7R at LeMans... I know there as a German team that ran it, Conrad Racing maybe? Too many projects since then to remember. It's a shame Saleen is gone, I really liked those cars.

redzcstandardhatch

in the "intake manifold thread" i said my manifold was 2 liters (for a 2.3 liter).

i meant 2 two liters. so its 4, kinda. about 2 pop bottles (scientific huh?). i was in a hurry at work, sorry! i went on the 1.25-1.5 rule roughly when designing it.

biggest one you can fit in the engine bay!

Tjabo

Thanks guys, I appreciate the input very much!