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Originally Posted by scotty305
Nice Matlab code, I used Matlab in school but never got around to using it for fun car stuff like this.
I have one comment and one question:
1. I knew some people who built a variable-volume intake plenum for dyno testing... it was essentially a box with fixed runners and a sliding lid (the throttle attached to the lid), sealing it was difficult but slightly easier than fabricating multiple plenums.
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I didn't even think about doing a variable volume plenum. Honestly the requirements of such things for sealing it would be a little too much for positive pressure tuning. Consequently I have not seen any mathematical model to which I could digitally model the results for it.
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2. Is there a way of predicting the relative power gain or loss due to resonance tuning? For instance, if you could somehow predict that there would be a X% gain in power at the resonant RPM but a Y% loss due to some sort of antiresonance elsewhere, you might try runner lengths/diameters that not only maximize gains in your desired powerband but also minimize losses.
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I doubt very much you could hope to tell how much torque you'd gain at a specific RPM. Based off the 26B the torque increase is a rather small percentage of incorrect length intake. There's also too many variables to stat that intake runners and a plenum volume will have this effect on a car: The difference between one car and another in power really comes down to the whole shebang. Intake, Combustion quality, Exhaust, rotating mass of the drive train, and even atmospheric conditions. You'd honestly have to hold 4 of those things constant just to test the effect of one--and even then I'm not sure that holding them constant would give realistic results.