blow off valve [Archive] - SaabCentral Forums

: blow off valve

25th June 2002, 11:55 PM
what is the best blow off valve for saabs and how hard are they to install?

Janne Selinummi
26th June 2002, 04:11 AM
Not much trouble, you just need connections on the IC-throttle body pipe and the AMM-turbo pipe. After that it's just plug and play, pretty much.

I would recommend the Bosch valve that's designed for higher boost levels - the one that's used in the 9-3 Viggen. That's a recirculating valve, and will last much longer than standard T16 BoV, while still being much cheaper than many valves around with similar performance.

If you want to keep your turbo and exhaust manifold in good order, you need a recirculating valve; the atmospheric ones will cause excessive fuelling with BoV activated in cars with air mass meters.

26th June 2002, 04:53 PM
yeh, you can't use an atmospheric dump valve on a car with maf/amm. got to be recirc

While we're on the subject, my '99 9-3 has the T5 ecu and so I can use an atmo dump valve, but I have heard since the spring is so strong that it takes a second to open it which can cause more lag and possibly damage the turbo.

anyone got an atmo dump valve on a T5 car?

Janne Selinummi
26th June 2002, 05:36 PM
Those atmospheric valves that I'm familiar with open pretty much instantly, and by no means is there a second-lasting delay.

If the atm BoV is a good one, it'll work fine with Trionic 5. You probably don't
notice any improvement in throttle responce over the stock recirculating BoV, though, unless you're running so much boost as to require more dumping capacity than the stock valve can handle.

Atmospheric valves are the ultimate dumping device, and that's why they're used in motor racing. A hard spring that causes kind of lag you described means either a product with a design error, or a broken item IMHO.

26th June 2002, 06:20 PM
Thanks Janne...I've been looking at the Forge model at, i've heard good things about it.

what about problems with the valve remaining closed at idle...? did you ever hear of this?

Janne Selinummi
27th June 2002, 03:41 AM
Some people have experienced idling problems, but this, again, is more a matter of the respective product not being suitable for the given application. It's common for diaphgrams to rupture, and that causes idling problems. It's best to get a valve with piston instead of diaphgram. Better still, a piston dump valve with adjustable sensitivity should be enough to counter all the associated problems dump valves might have.

28th June 2002, 03:35 AM

The valve is meant to be closed at idle, its when its open that problems occur as the amount of air that the mass meter records isn't the same as the amount that enters the engine.

If you're running an atmospheric valve then a balanced twin piston design is best, but even so it still must be one suitable for use on cars fitted with AMM. The Forge design is one, the Bailey DV26 is another.

28th June 2002, 10:27 AM has problems staying closed at idle. I should have worded it "there is a problem with the valve being slightly open at idle when it is supposed to be entirely shut"?

edited to say my car is a T5....are you familiar with the T5? it does not use an AMM

<font size=-1>[ This Message was edited by: conradFL on Jun 28, 2002 3:54pm ]</font>

29th June 2002, 02:27 AM
this is great stuff better than going to school.the question is how do you know that the diaphram has busted

7th July 2002, 07:41 PM
<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR size=1 color=black></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>how do you know that the diaphram has busted </BLOCKQUOTE></FONT></TD></TR><TR><TD><HR size=1 color=black></TD></TR></TABLE>

Take the valve out and blow in to it through its lower pipe. If air come out the other end it's busted. If air doesn't come out it works.