Resonant airbox

A.FreeMan · Derestricted Danger Joined: 15 Feb 2016 Karma :

Hello everyone,

So I was at the garage yesterday doing some dyno testing: I shortened the inlet pipe to the airbox in 25mm increments and ran a dyno test each time.

I have previously calculated the resonant frequency each length should correspond too. (at resonance, more air is shoved into the intake)

The results weren't conclusive, there were peaks in the torque curve that shifted up the rev range with each cut. They didn't however truly correspond to the expected rpms.

HOWEVER, I theorised that at 1/2 the resonant freq, and 3/2 the resonant freq we would see dips in the curve. Anti-resonance.

The results DID coincide with the expected dips. Pretty accurately.

Is this a load of tosh or is antiresonance a thing (in terms of resonant airboxes - i know there are such things as antinodes etc when dealing with harmonics in maths etc)

Sorry i can't upload the results - the guy couldn't email them to me so all I have are handouts which I don't have on me.

Just to summarise - I am asking whether it is possible that by tuning an airbox to resonate at say 5000rpm, will there be a DIP in the torque curve at 7500rpm, (and another boost at 10000rpm) ?

The dip is all I am interested in.

thanks
Alfie

PS. Shortening the inlets did give +5hp at the top end ~10000rpm!
(and also misfiring in the mid-range - anyone know why scientifically?)

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

My understanding is that there are ancilliary "power jets" in the carb which fill in a hole in the midrange fuelling.

Presumably you've moved the position of this hole?
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