Dump Valves?

[Dingo]

I'm need a new dump valve but my question is whats the difference between the stock s2 valve and the s3 dump valve apart from the price and does one have a stronger spring than the other and if so will this make any difference to the characteristics of the engine?

[Jamo]

Stock dump valves are not spring based they are diaphragm based.

The S3 has a stronger diaphragm

[UrS4boy]

Stock dump valves are not spring based they are diaphragm based. The S3 has a stronger diaphragm

Huh? Of course they are spring-based. What do you think holds the diaphram closed when not under vacuum??

http://www.s4biturbo.com/art-dvtests2.php

[Dingo]

Ok but will this make any difference to the charteristics of the engine? ie: will it boost stonger, quicker, longer or will it make no difference at all

[UrS4boy]

Ok but will this make any difference to the charteristics of the engine? ie: will it boost stonger, quicker, longer or will it make no difference at all

Bypass valves, as used on the Audi I5 20V turbos, are intended to help prevent the turbo from being stalled when you take your foot off the throttle. Blow-off valves (BOV) (the real "dump" valves) just dump the extra pressure that occurs when the throttle slams shut. However, the Bosch Motronic system is not happy with this approach because it has metered that air and if it is dumped, the calculated fueling will be off and the mixture will be off (too rich) for a short period when you do get back on the throttle.

As a result, BPV are better for a Motronic equipped 20V turbo (re: emissions and transitory power). A BPV that has a firmer spring and a diaphram that is more resistant to tearing over time will help your car to perform better, especially between shifts. It will NOT increase your overall boost or horsepower. Only the turbo, the injectors and the ECU can do that.

Here is a bit more reading for you:

http://forums.audiworld.com/s4s6/msgs/150046.phtml

Hope that helps.

[Dingo]

Ok Thanks S3 one it is then!!

[Jamo]

Huh? Of course they are spring-based. What do you think holds the diaphram closed when not under vacuum??

http://www.s4biturbo.com/art-dvtests2.php

Eh? search the net there are two types of dump valves, spring based and diaphragm based

[k.alle]

The dead OEM bypass valve that I took apart (diaphragm) certainly had a spring in it, don't they all?

[Fat Audi 80]

[S2central.net]

What jamo is tryin to say is the oem valves have a diaphragm actuator, but aftermarket ones have piston actuation. BOTH types use a spring to close them AFAIK.

[UrS4boy]

What jamo is tryin to say is the oem valves have a diaphragm actuator, but aftermarket ones have piston actuation. BOTH types use a spring to close them AFAIK.

No. What I hear JAMO saying that an OE Bosch 710 series (A or N) has no spring inside. Which is wrong. If he would open up the two links that I gave, he would see that he is wrong and you and I are right: There is a spring to keep the diaphram shut.

No where does JAMO say "piston".

However, he is now probably "pistoff".

[Rusty]

As I have it in my head, the piston type is stronger as it's solid metal vs. plastic but more expensive as a result.

The diaphragm ones can puncture meaning that they don't hold boost and chatter like an S1!

I think I'd go for one of the new style recirc valves that act as a BOV at high boost. Take a while to setup apparently but worth it for some noise when you're playing and silence when your not. Or just cut the airbox and it'll chirp away no matter what you fit!

[UrS4boy]

Eh? search the net there are two types of dump valves, spring based and diaphragm based

JAMO: Whoever did that diagram and labeled the moving part a "diaphragm" (or diaphram in simpler English) was wrong. That *thing* is a piston (not the same as a diaphragm). I believe FORGE BPVs use pistons and O-rings to control the air movement.

Either way, as Paul N. pointed out, both piston and diaphragm type BPVs use springs to keep the piston (or diaphragm) closed until there is a vacuum behind the throttle plate (e.g. between shifts).