Boost Flutter - Page 3 - Perth-WRX.com

munya · #21 07-06-2010, 12:50 PM

Quote:

Originally Posted by smerm07

i don't get any sort of "flutter" and im running a vf34/p20 @ 20psi on my audm my04 wrx.

I get flutter on part throttle @about 1.2bar on my vf34 p20 but none on full throttle

MY99 · #22 07-06-2010, 01:10 PM

Quote:

Originally Posted by blommer

there's a reason why VF35 is used as a standard turbo for the AUDM GDBs. It has a smaller compressor wheel and had P15 housing as compared to the VF34. AS the AUDM heads are smaller, the amount of air entering is restricted, thus creating the flutter. Upboosting the VF35 will also cause fluttering as there's only 1bar or so of boost the AUDM can take in efficiently.

Whereas the VF34 came standard on JDM GDBs because it had bigger ported heads to complement with it.

In that case, wouldn't these cars be "fluttering" at full throttle, full boost also? They only seem to flutter at part throttle, at lower RPM suggesting that the problem stems from the tune, not the restrictive heads. The turbo is blowing more compressed air than the motor can take in causing the compressor to stall. If the heads were the cause, then this would happen at higher RPM aswell, right?

joey89 · #23 07-06-2010, 01:31 PM

Im with my99 on this one if its because of the restrictive heads

How come it happened on my vf39 at 19psi

and never happened with my vf23 at 19psi?

Pretty sure there was a thread about this awhile ago and said its normal happens with some vf series and some dont

Hurtenstein · #24 07-06-2010, 01:37 PM

um, 1psi boost is pressure that the heads cant take in.
If the heads could take all the air, there would be no positive manifold pressure...

Mister Two · #25 07-06-2010, 01:40 PM

Quote:

Originally Posted by joey89

Im with my99 on this one if its because of the restrictive heads

How come it happened on my vf39 at 19psi

and never happened with my vf23 at 19psi?

Pretty sure there was a thread about this awhile ago and said its normal happens with some vf series and some dont

Because the vf23 has a slightly smaller compressor wheel and a much bigger (p20) exhaust housing.

This results in lower air flow through the turbo at low rpm when boost is beginning to build up. So because the turbo isnt out flowing the heads during this time you dont get compressor surge.

joey89 · #26 07-06-2010, 01:50 PM

it had a P18 exhaust housing on it same as a vf39

Mister Two · #27 07-06-2010, 02:08 PM

it still has a smaller compressor wheel. so flows less air at the same shaft rpm compared to the vf39

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