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-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

It sounded cool the first few times, now it's just loud and obnoxious

I'm running it open to atmosphere. Plumbing it to recirculate would be a really big pita. What other option is there to quiet it down?

I'm running a Forge Motorsports valve that you can see here:

It doesn't have a horn or any other sound-increasing gizmos. It's just plain old loud.

ps- at idle I have positive pressure coming out of it - telling me that the turbo is pushing more air than atmospheric even at ~1100 rpm. Is this normal?

nick

OutOfTheBox · Joined: 31 Mar 2006 Posts: 434

stick a sock in a coke can and away you go

sound is high frequency

high frequency = very directional & bounce off hard stuff.

turn the dump the other way, make whatever comes out hit a soft something.

sponge would be better than an airfilter

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

RIPDOTCOM · Posted: Tue Jul 04, 2006 4:34 am Post subject:

best way is to recirculate or buy a quieter bov

bass gt · Posted: Mon Jul 10, 2006 8:48 am Post subject:

Nick,

It seems you have a recirculating type of BOV. I believe these will allow recirc under low load conditions, clamping shut once the boost rises sufficiently. You need to either plumb it in or change it to an atmos dump type.
I am thinking of fitting a re circ type to my racer, but i'm going to speak to Bailey motorsport tomorrow to get some advice.

Steve

P924 · Joined: 14 May 2006 Posts: 57 Location: Belgium

What an engine... WONDERFUL

_________________
924 1981
911T 2.2

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

This actually is bypass valve not BOV indeed.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold

'84 924, turbocharged, sold.
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endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

Mr_Bob · Joined: 15 Aug 2006 Posts: 23

Put a pcv filter on it.

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Despite your unnatural love for carburetors, this is actually a good idea

Cheers!

Dagwood928 · Joined: 22 Nov 2003 Posts: 65

I think if you even put a pipe on the end put a bend in it and vent it down out the bottom of the engine compartment, you could effectively change the frequency and dampen the noise a bit......kind of like long straight pipes on an exhaust.
2 cents

Darren

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Solved

With some help from Mike Lombardi @ Forge Motorsports (great guy!). He told me that facing the valve in the stock direction makes a higher pitched sound than if you simply swap the inlet/outlet sides.

I made the change, and also stuffed a clean shop rag into a cheap breather filter that the outlet is plumbed into. Now I just get a very faint, and very acceptable, "pshh" as opposed to the mind-jarring "PSSTTT" that would echo off houses on residential streets!

Not a boost spike to be found even with the rag damping the sound.
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet