99taws6

iTrader: (2)

Ok, I am posting this in hopes of getting some answers as ATI doesn't seem to be on the right track troubleshooting this.

I have a 04 GTO with an A4. I have a D1SC with a 4" pulley. I am making about 7lbs of boost right now. I have the ATI FMIC and all their kit (completely stock)

When cruising around with minimal pedal input right around 5-0in Vacuum the bypass valve whistles at a very high pitch. This sound goes away instantly when you blip the pedal and hit 0in vacuum. The sound is very high pitched and is like nails on a chalk board.

ATI suggested flipping the diaphram housing 180deg and that did not work. They also suggested moving the hose barb from the back side to the other side of the diaphram housing. This would be fine if the hole on the other side was threaded!!!!

So I am curious if anyone else has had this problem or might have any suggestions for me. It is an annoyance more than a problem as it doesn't seem to mess with performance.

I searched the net and all I found was a post on a mustang forum about the allen set-screw being adjusted wrong from ATI. They claimed that there should be about 1/8" of the allen screw above the locknut. Mine is about 7/16", but ATI says they are adjusted from factory...

Thanks in advance for any help and sorry if I rambled...

alwaysinboost

its not the BOV its the SC... my F1 does the same thing, don't worry about it its normal.
the reason you hear it at the bov is cause its open while you're crusing. try a different, air filter on teh SC, that should change the sound some.

99taws6

iTrader: (2)

well my tuner and ATI think it is the BPV. They compared it to blowing over the open end of a coke bottle. I can hear the SC noise, but it is a different sound. I will see what a filter change does though.

Thanks

rufretic

iTrader: (37)

If you don't like the sound your best bet is to route the air comming out of the bypass back into the intake side of the blower.

99taws6

iTrader: (2)

Its not a normal sound is what I am getting at. I love the procharger sound and the normal sound of a bypass valve. ATI doesn't make a kit for the A4 GTO's and therefore it is not a normal sound. I'm gonna make it work, just wanted to see if anyone else has had a similar problem. We are thinking it might be the vacuum difference between the M6 and A4 cars. I will post up when we figure it out.

EPP

iTrader: (22)

On the Camaros and Firebirds we relocate the vacuum to the bypass valve back to the firewall and T it off the hvac line, this eliminates the fluttering sound we sometimes get. You might want to experiment with your vacuum source. Bob

Jake@EPP

The way the swing arm is designed is the issue. The arm can somtimes be bent just enough to bind up and not move freely, this would cause a stick untill you go WOT or experience alot of vac in a quick time. Just the right pitch of the blade will cause this.

A swing arm for a BPV is not the best design, a air over valve design is far superior.