Dump Valves

[Raf]

this is rather a general question.... how does a dump valve work? and does it have and impact on anything (i.e accelration, performance, consumption etc etc) apart from making a sound?

im not sure if they are purley cosmetic or if they serve a valid purpose?

[Lauren]

The general idea is that because a turbo is positioned before the throttle body, when you lift off to change gear/decellerate the throttle obviously closes, but the turbo is still spinning.

The effect of a closed throttle will effectively stall the turbo, so a 'dump' or 'blow off valve' (same thing) releases any excess pressure created by a spinning turbo and a closed throttle, to enable the turbo to still spin or really to stop it having to cope with the stresses of stopping suddenly. Theory is that it helps spool up times on the turbo and reduces lag.

There are two types, one is the vent to atmosphere whereby the BOV vents straight to atmoshere with the accompanying PTTTTTSSSSSSSSSCCHHH sound or the more common with car manufacturers recirculating BOV which allows the air to recirculate through the intake and thus relieves the pressure in a more civilised way (ie its quieter).

So yes they do have a job to perform. How much of an actual effect they have is enough for quite a long debate.

HTH

[Sidewinder]

PTTTTTSSSSSSSSSCCHHH

Spot-on Lauren with your attempt to type out the sound.

[Merlin]

If you are fitting on a rev1/2 you will find that you will use a tad more fuel, on a vent to atmospher BOV, as the car will run rich for a moment every time it goes pssstsshhhhh! I use a HKS SSQV Which I think is the daddy!!!

Regards
Rob

[Adam Tyler]

I have heard of and experienced problems with using an atmospheric BOV on a Rev 1. The car was prone to engine stall ocassionally so I re-connected the pipe to re-circulate. I have been thinking of disconnecting the pipe again to get the noise, could I cause any serious problems or just annoying ones?

[Merlin]

well, i have had a vent to atmospher type bov, on all of my rev 1's and have had no problems, just dont use a crapy cheap one, think that where the problem lies, something like a hks or a blitz or greddy,, what u need ia a good piston type unit, you shouldnt have any probs then

regards
Rob

[Chris \'aka rustboy\' Amm]

well, i have had a vent to atmospher type bov, on all of my rev 1's and have had no problems, just dont use a crapy cheap one, think that where the problem lies, something like a hks or a blitz or greddy,, what u need ia a good piston type unit, you shouldnt have any probs then

regards
Rob

HKS can be made to recirc i believe and i think you can adjust it to how much it dumps.

[Driftlimits Performance]

Hey Merlin!

Is your HKS SSQV standard or have you got any of those gold/purple fins? Has it got a really high whistle to it?

I *think* mine has a purple fin which is meant to release a lower sound. But the whistle is still a bit high for my liking.

cheers