tici

iTrader: (1)

In reality I wanted to write “my bypass valve is farthing”, but this word doesn’t belong in the thread name
But it’s real: as soon as the manifold pressure goes close to -1PSI (-2 inch Hg) it starts to sound like a horn! This happens only during slow accelerations, if I mash the pedal there is no weird sound.
It’s the Bosch bypass valve supplied in every Vortech kit.
I can imagine that as soon as the pressures before and after the throttle body are the same the rubber membrane starts vibrating

Or is there another explanation?

How can I solve this problem?

Thank you - Stefano

Blackbird

sounds like it's leaking, shouldn't make any noise.

check your connections

black_yukon

Time for a new one. The Bosch bypass is prone to tearing around the internal rubber diaphragm. The fart noise is air passing through the tear. They are cheap though. You can get them through any VW dealership.

greentahoe

iTrader: (2)

Those things arent all that great. I stepped up to a racing bypass.

tici

iTrader: (1)

Is it dangerous to drive with the farthing valve? On another forum a guy had his blower broken because of a damaged bypass valve
Under boost it's not leaking and builds up the supposed 6 PSI.

If I go for a different style what brand do you suggest?

Thanks - Stefano

black_yukon

Check out the Vortech mondo. If you want a drop in upgrade, troll around the turbo Audi/VW forums. Those cars also come with the Bosch 110 valve. A lot of those guys are going with Forge motorsports direct replacement valves that are machined aluminum.

tici

iTrader: (1)

I checked my bypass valve and it's fine (no leaks, opens closes as it should).
I installed it reversed as a friend suggested and the noise is gone!
I don't know if it's correct or dangerous: I'll try a couple of days and see what happens

Got Me SOM

iTrader: (2)

i don't think that's a good idea, just doesn't sound right. think of a one way check valve now opening the opposite direction it should. just replace it.

tici

iTrader: (1)

I know it's wrong, but the valve really looks like new. What can be different in a new one? Better (stronger) spring?
Is it possible that the hose to the brake boost line makes a difference? Let's say if it's too long/short or wrong diameter? Maybe it's just the distance that induce some kind of resonance... Or also the hoses between the aluminum pipes and the bypass valve?
I'm not trying to save money, but to understand how it works

black_yukon

Buy a new valve. It is making the farting noise because the internal rubber diaphragm is torn, something the bosch valve is notorious for. If I am wrong and the new valve also makes the farting noise, you could always return it to the parts store. Check here for more info http://www.s4biturbo.com/art-dvtests.shtml

greentahoe

iTrader: (2)

The vortech Racing Bypass is usually like $170 or so. I picked mine up on EBAY brand new for $80. They are on there all the time.

tici

iTrader: (1)

Interesting link! I'll see what I can find over here (ebay or so).
However: the valve isn't leaking and works properly and the diaphragm look fine (as much as I can see).

Somewhere I saw that there was an upgraded Bosch valve, mine has those numbers:

040 - 0280 142 102

Any idea?


Vortech racing bypass: you mean the Maxflow od the Mondo valve?

tici

iTrader: (1)

Bosch has an updated version of this valve (#0280142108
). The old part # was 0280142102.
I installed the new one in the original Vortech direction and the farting sound is gone!
The old valve is well known at the Saab forums as "hooter valve" - all clear about the sound.
The new valve has a brass disk with a hard rubber seal (like an O-ring), the old valve has a soft rubber membrane that can vibrate at certain pressure and air flow conditions (HOOT!).
The spring is stronger than the older version. This allows boost at lower RPM, an you can feel it!
Here two links about this subject:
http://www.socalsupras.com/tuning/bypassvalve.html
http://www.quasimotors.com/hooter.htm