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Manufacturers have also used Helmholtz resonators for wave ram effect at low rpm (diesel apps).
Yes, the majority of benefits are going to come elsewhere, however the air still enters at the air filter at all rpms and throttle conditions... so, perhaps it's the wrong view to consider it a more crushed or disturbed "slinky", but air still has to come from point A and slinky it's way back to end up at point B (at least in my mind and not accounting for inertia effects, etc).
I swapped a 1.8L mazda BP into an MX3 years ago and I recall there being an H-box inline with the flapper MAF (most of the boxes seem to be placed after filter, off to side, or whatever). On that particular car, even if it 'shouldn't' have, torque output decreased removing the h-box. Mazda was big into their resonance tuning at that time, but perhaps its more likely that it changed something with the MAF or air going through MAF and that was the performance drop I felt at the time.
At any rate, for the Suzuki - the longer pipe definitely reduced some objectionable noise. Also my perception to torque, etc.. changed, but it would be nice to put it back on the dyno to have actual data. The car gained a few more mpg, but this could also have been attributed to changes with my right foot or the MAF.
The big drawback is that just like a CAI, it changed how the air goes through the MAF and thus altered the MAF signal and thus effects results. When I say these MAFs are sensitive, I really mean that they are sensitive. I can take this car from 18:1 lean at part throttle, to 11:1 rich at anything over 10-20% throttle just by changing pipe diameters, in front of and behind the MAF.
I datalogged a few of the runs with the wideband against tps and rpm for future reference. This also alerted me that this car is going too rich too early and of some other issues. Going to fix part of those issues for the next tank.
This is just more a comment that some of these tweaks really will be vehicle specific. Like I say, CAI likely will cause problems on a hot-wire MAF type vehicle just because of the design of the sensors. If the ECU doesn't compensate well enough, you could see very little or no performance increase, and less mpg.
If you have a Honda or some other commonly MAP sensor based vehicle... you may want to try cramming as much air down the throat as you can to see what results you can obtain.
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1992 - Suzuki Swift GT
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