[vex]

Originally Posted by NoDOHC

Be careful applying Speed-of sound math here... If you do a good job on the plenum, you should be able to mostly ignore the effects of the compressibility of the air. Most of your resonance tuning is due to the Helmholtz effect (AKA: organ pipe, more of a dynamic systems model than anything to do the compressibility). The air in the plenum should not be moving anywhere near the speed of sound.

Understood. I doubt very much that the velocity of the intake stream will be higher than .6M which minimizes compressibility of the air. If I maximize intake velocity then wouldn't that mean that I have the ability to pull higher velocity air into the intake stroke for a higher torque curve? As for the Helmholtz effect, would actually tuning for that even though I'm turbo'd be beneficial? I suppose for cruise when I'm not in positive pressure it may be beneficial though I'm having a hard time reconciling the previous posts mathematics with my engineering brain (units don't add up). Is there a full formula somewhere that I may be able to tinker with?

Don't think about this too hard man, intake manifold are simpler than they would initially seem. Don't ever try a dynamic model on a manifold unless you are a glutton for punishment (I have tried it, it is not easy).

I have access to CFD software and already have the wherewithal to create digital representation of the manifold in a few hours time. From my understanding once I have that all done and taken care of it shouldn't be more than a few more clicks and having it run to numerically solve the flow potential.

Basically, your air velocity will follow the offset-sinusoidal waveform typical of an infinite-length-connecting-rod reciprocating engine (or a rotary, which has similar characteristics). The pressure drop at each transition is easily determined by using the lookup tables in the back of your fluids book, no difficult math required. Basically, you can get easy cross-sectional area requirements by taking the peak flow into the chamber and dividing it by the desired velocity (no rocket science there).

Don't have a fluids book I have an aerodynamics book, a couple ocean engineering books, and thermo book. I'm currently taking a compressible aero course but no fluid tables for different offsets.

With the plenum, everyone has their own idea as to how bast power is obtained. I won't take to time required to explain my opinion on that. As I said before, you can easily find the flow through any given portion of the manifold at any given time with reasonable accuracy.

I will venture to say that I have seen tapered plenums, log plenums, cross rams, tunnel rams, inboard velocity stacks, tapered tubes, straight tubes, etc. in operation and I have not seen the simple log with beveled, constant cross-sectional area runners beat yet.

I imagine that the velocity increase from velocity stacks, tapered tubes, etc wouldn't yield a high enough velocity increase to matter.

I hope this helps some. I know that math is awesome, but don't let it bog you down. Seriously, I found that going by my intuition and what feels right is often better than trying to crunch crazy numbers, there are too many x-factors to make any good simulations given the typical person's toolbox.

I'd hate to be argumenitive (and I don't want to come off like that) but I do not have the typical person's toolbox: CFD, Numerical analysis, and a hand full of individuals that have 800+hp cars. I've bounced my thoughts and what I am thinking off of them and they seem to be of the mindset to use the CFD software to ensure proper air distribution to all runners is key in plenum design. I appreciate the information that you're giving to me and by no means am discounting it off hand, i'm just trying to learn as much as I can in as little time as possible.

Edit: I hunted high and low for an intake manifold gasket and only succeeded in concluding that it is high time to clean out the garage (I know I have two brand-new ones, somewhere).

Can I take a scan of a LIM for you? (I can find that...) What measurement do you need?

It's okay, I don't want you to break you scanner. I may actually be getting a LIM in the not too distant future to take the measurements off of myself. But if you're wanting to do it you'd just need to scan the profile of the mating flange, and measure say a mounting hole diameter. This sets a scale for a digital copy and will allow me to pull the measurements off the copy with out worrying if they're right.

Basically Dreal/Dscale=Dreal/Dscale: 10.5mm/1.25mm=Dreal/8.9mm; Dreal=74.76