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Dump Valve

Some people reckon you are better off without any dump valve for the hassle they cause, but that's another can of worms ;).
 
I fitted a Vitesse MAF to my turbo - this made the noise of the recirc bypass valve much more noticeable - and gave you a bit more induction noise. To be honest I would have preferred it to stay silent.
 
I would only use a recirculation valve because of the ridiculous noise, and recirculating the air to the compressor inlet should help with spool when reopening the throttle.
 
A well timed post. I replaced the standard recirc valve with a used Bailey DV30 but have since acquired a 993 turbo valve which is externally visually identical to the 944 part bar the part number but it does have a metal piston inside.

The 993 valve stays up if you push the piston up and cover the vac port with your finger whereas the 944 one does not. I can't be sure (will need to remove it to check) but not sure if the DV30 piston stayed up or not.

Any ideas as to whether there is a more scientific test or which is better the DV30 or 993 (I know which looks better)?
 

ORIGINAL: Eldavo
The 993 valve stays up if you push the piston up and cover the vac port with your finger whereas the 944 one does not
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The vacuum port controls the opening of the valve, so when the engine is running under full vacuum (throttle closed), or if you push the piston then plug the vacuum port, the piston should stay open. From what you describe the membrane in your 944 valve may be broken.
 
ORIGINAL: 944 man

'Dump valves' dont suit any car, really. The proper term is air bypass valve and in keeping with most turbocharged cars built since 1980, the 944 Turbo already has a recirculating air bypass valve.

You can end up with a situation where the standard part isnt up to the job, but vent to atmosphere valves are all about showing off and very, very seldom required. Unless youre fitting a VTA valve with a duckcall, in which case it will be perfectly acceptable and quite funny. On ScoobyNet I always used to advise eager new members asking about 'dump valves' to leave the car as it was and simply rev it at traffic lights whilst shouting "Im a c*ck!" out of the open window. Same effect and your car will still run properly, which it wont with a VTA.
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Ha, Ha, Ha!!! PMSL!!! ******* Quality!!![:D][:D][:D]

John Sims: Grow up [:mad:]
 
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