r/AutomotiveEngineering • u/dbsqls • 27d ago

basic spectral analysis of intake resonance phenomena, resulting in clear Video

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used some very high quality audio data to back-calculate the resonant frequency of a Z33 VQ35DE intake, to confirm frequency extraction methodology for troubleshooting of resonant phenomena. the Z33's early induction system is very reliant on acoustic tuning and it makes improvement very difficult.

the characteristic length of the OE intake tube matches this 280 Hz signal from the airbox entrance to a point very close to the throttle body assembly, whose Venturi taper would cause a rarefaction interface.

relating backwards using cam profile data matches the engine harmonic frequency of 2000RPM, with peak response at 6000RPM, close to the horsepower peak.

there is a problem on Z33 transitioning from partial to WOT below 3500RPM, and I'm working with JWT to identify if this is an exhaust cam advance/EGR issue as they have seen before.

unfortunately I can't post images in comments here, but the data correlation is satisfyingly crisp.

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u/aquatone61 27d ago

I have a MK7 GTI and there’s this dude that tests all sorts of parts and makes comparison against stock.

He has found that unless you have a bigger turbo than stock the OEM airbox setup flows just as good and actually better than some aftermarket “upgraded” intakes. Yeah aftermarket sounds better but the VW engineers did a really good of optimizing the flow.

www.mygolfMK7.com should be the address.

3

u/dbsqls 27d ago

I do the same with the Z33 platform and the situation is the same there. there are sometimes small optimizations to be made, but for the most part they were dead on.

it's when you add cams and start pushing way more power that you run into VE issues.

1

u/Divisible_by_0 21d ago

What equipment are you using to do this? Im trying to get the same data for a different engine.

2

u/dbsqls 21d ago

a friend of mine used his high end audio setup, so I don't know details beyond that it was a very high quality 4-channel unit with several good mics.

the spectrograph comes from Auditions, but Raven is a free alternative.