Intake Design Exploration

[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.

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).

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).

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 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.

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?