Been researching ITBs for my 3.6L C30A and am wondering how to determine ideal plenum volume, if there is a formula to do it, and if it's even possible to effectively measure resonance and frequencies by an "enthusiast."

The only formula I can come up with (net research) is NL=84000. N= engine rpm, L= distance from plenum entrance to the head of the intake valve. But I don't know if that was for a carb'd car or fuel injected or if I'm missing anything else or off track completely.

Any help or point in the right (or better) direction would be extremely appreciated. Thanks!

 

You will want to run two separate plenums, otherwise you will get interference through your firing sequence.

What is your current runner length? If you are running a shorter runner you can compliment it by running a larger volume plenum (1.2-1.3 x displacement for higher peak torque). The opposite applies as well, a longer runner can be complimented by a smaller plenum volume, (.8-.9 x displacement for lower peak torque). Or you can aim in the middle.

A B-series engine usually likes a plenum volume between 1.2-1.5 x engine displacement depending on compression and intake cam duration. This will give you a broad torque curve that doesn't run out of steam up top. Unfortunately your C30 could react differently.

If your motor is using a stroker crank, which seems likely due to the 3.6L displacement, you're peak torque will be pushed further down in the RPM range, so assume a 500-1000rpm decrease in peak torque. If you want to make up that loss in RPM you can use a large (~1.5 x displacement) plenum volume.

Have you decided on a shape yet? Remember that air in motion behaves as a fluid, you want to have just enough of an organic motion to promote healthy flow, but not enough so that the air hugs the walls and doesn't fill and separate. If you have access to a CAD program like SolidWorks, CATIA, or Pro/E, I can import those files into my CFD software and perform some flow simulations.

 

oh man he totally beat me to that ..... i was goign to say the exact same stuff.

j/k

that was a really good read , and great info

 

-

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR &raquo;</TD></TR><TR><TD CLASS="quote">You will want to run two separate plenums, otherwise you will get interference through your firing sequence.</TD></TR></TABLE>

That would be better but I don't want to deal w/ the complexity and extra weight of it. What would be even better would be a nice variable intake like an F1 car.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR &raquo;</TD></TR><TR><TD CLASS="quote">What is your current runner length? If you are running a shorter runner you can compliment it by running a larger volume plenum (1.2-1.3 x displacement for higher peak torque). The opposite applies as well, a longer runner can be complimented by a smaller plenum volume, (.8-.9 x displacement for lower peak torque). Or you can aim in the middle.</TD></TR></TABLE>

I wish I knew what the current runner length is. Really, it should just be what a current C30 is since I don't ITBs currently.

I'm just now getting "it" in regards to what I should really be asking. I should be asking where I want my peak torque to be: higher or lower RPM. I'm fairly sure I'd like the power to be on the top end...with the caveat that there's still a fair amount of drivability at lower RPM (3500-4500). If the top end losses to much bottom, I'll shoot for the middle. It seems like some of this is just something that I'll just have to experiment with actual mock-ups.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR &raquo;</TD></TR><TR><TD CLASS="quote">If you want to make up that loss in RPM you can use a large (~1.5 x displacement) plenum volume. </TD></TR></TABLE>

That's what I was thinking as well. And yep, it's got the stroker crank but also a slight bore job too.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR &raquo;</TD></TR><TR><TD CLASS="quote">Have you decided on a shape yet?</TD></TR></TABLE>

Not yet. But I know that it needs to be tall enough so that the air can bend w/o too much disruption. I'm thinking of something like this:



Twin air boxes total, one on each side leading to a central plenum. As of this moment, I'm entirely opposed to any kind of hatch induction especially that gawd forsaken NSX Super GT shark fin and the above pic is one of the better setups I've seen.

Planning on using ScienceofSpeed/Hayward's ITB system. Looking for their air horn length and diameter specs now...

Thanks a bunch for your help - really appreciate it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Pixel_NEM &raquo;</TD></TR><TR><TD CLASS="quote">Solidworks isn't equiped with FloWorks. Even the premimum version doens't have it. I have seen some crazy stuff done with ANSYS software.
</TD></TR></TABLE>

For imported files from SolidWorks, CATIA and Pro/E we use Upfront CFD from CFDesign (cfdesign.com). For doing simple point flow analysis and orifice design, I use STAR-CD due to the ease of setup and quick results.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ponyboy &raquo;</TD></TR><TR><TD CLASS="quote">It seems like some of this is just something that I'll just have to experiment with actual mock-ups.</TD></TR></TABLE>

Thats exactly what you have to do to make a design do what you want. Theory of design will get you 80% there, the other 20% comes from testing. I would see how the engine responds with the ITB's first. You are going to be limited by package size I imagine with the NSX engine bay the way it is.

 

Thanks for the book recommendations (via PM). Thought you'd get a kick out of this white paper, if you hadn't read it before.

Looked though the SAE website and saw diddly on intake theory and design. They have a bunch of other good stuff though.