As per subject heading. Once heard it mentioned by a boy racer type but his garbled explanation left me even more in the dark. Is it a performance thing or an aesthetic thing?

Scooby's have a dump valve as standard. The main reason for a dump valve is to release 'unused' boost pressure from the turbo. if there wasn't a dump valve the unsed air pressure would be forced back on the blades of the turbo shortening it's life.

By changing to an external D/V you get the famous pppppppppphhhhtush that all Nova drivers want.

It's a personal thing. Unless you seriously mod your car then you will need to upgrade from the stock item.

I think that's right but please correct me if I'm wrong!

So in fact there is no purpose, and all those that have fitted them are guilty of "MAXPOWERITIS"

id - the doc has spoken

The Gilly, yeah simply put thats about right, there is a tendancy to get overcomplicated. The dump valve also keeps the turbo spinning faster enabling faster pick up after a gear change.

Treacle

well they do significantly reduce the turbo lag too, worth doing.

So im guessing that the external ones make the Tssshh noise? What do the internal ones do with the pressure and how come they dont make any noise?



Wol

Could be that the "dump valve mod" your acne-ridden friend refers to involves converting the standard recirculating dump valve into a vent to atmosphere one, making it pshhht a little more obviously.

Whether he's referring to altering this dump valve setup or buying another one though, the net effect is the same. As you say, giving it the ability to scare OAP's when you change gear.

Call me stupid if you want but, does a dump valve only fit a turbo car? If so have do the nova clan get the noise?

Nexaus: They have turbo'd novas, still a load of sh!t tho :p



Can the benefits of less lag etc be had without the loud noise? A quiet one would be ok. I couldn't entertain having a loud one due to the stick we give my friend on his mod'd Silvia ;).

Andy

You could record the noise on a sampler and play it at high volume through external speakers.

If you get a nice sounding one then its well worth it. The noise adds a whole new dimension to the car and I for one love it :D

I have a recirc dump valve but I still get that mad noise due to the APS induction kit - that's my excuse anyways ;)

I have a standard Dv but still get a whooshing sound from my Grahame Goode induction filter kit :D

I have a VTA but I would blow the recirc apart with my boost :)

HI, Long time reader first time poster LOL.

I know everyone always goes on about reducing Lag but I have found the opposite, not I can't comment on the scooby engine but on My R5 over the years I have tried many a differnt dump valve and personally I prefer none, the noise does get on my wick a little these days (getting old) and the Lag on a Standard T2 turbo is non existant, I recently ran 2 d/vs for a test and the lag was incredable!!

I saw stick with your std dump valve or silent diverter valve unless you want a bit of noise :)

Dave

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I have a VTA but I would blow the recirc apart with my boost
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What sort of boost do you run mate? the std ones must handle a fair bit a a friend of mine used to have a Type R and that as std (I believe) ran 16psi of boost?

Dave

I have been pondering the dump valve for a while and have some thoughts/questions.

If the throttle is closed at full boost and rpm, their is a large mass of moving air, this will hit the closed throttle causing a pressure spike of up to twice the boost pressure and a pressure wave to travel back up the inlet pipework. This reverse flow could damage the compressor and blow the pipes off. The BOV should dissipate this wave and protect the compressor and the pipework.

However if the BOV stayed open after the wave has dissipated, the turbo would then continue to discharge boost via the BOV which would cause the turbo to slow down quicker (This is a fundemental feature of the centrifugal compressor, maximum power is drawn at maximum flow)

I think the BOV should then only open when the pressure is above normal max boost. This is how the BOVs worked in F1 and on the audi sport quattro as I remember.

This is my thinking, what do you think ?

You're thinking along the right lines. Conventional blow-off valves aren't "clever" enough to get the balance of overpressure protection and pressure maintenance spot-on.

Best option to me has always seemed to be an electronically controlled valve. Initial opening in response to the ECU detecting throttle closure via the TPS, then duty cycle modulated to achieve optimal boost levels in the inlet tract, without unnecessary boost loss.

Have a HKS RSK and a HKS Sequential BOV, and don't listen to what others say. it spools the turbo up better between gear changes, so the boost is always there when you want it when the car is rolling.

weather this is different on a different model i cant tell you but on a STI-8 PPP with turbo back system it works fine but the HKS Sequential with HKS RSK is blimm'n loud, maybe a bit to much at times.

and there is nothing max power about a bov,

neons and filling your car full of heavy stereo equipment is, because that is all show and no go

[Edited by CTRnutter - 8/12/2003 5:53:45 PM]

[Edited by CTRnutter - 8/12/2003 5:55:37 PM]

Thanks for the reply/ies. I thought it must be an aesthetic (noise) thing 'cause I was aware of a dump valve's function but couldn't understand what the mod would be or what the need for it was.

[Edited by Bubba po - 8/12/2003 2:41:20 PM]