Silly question I know, but...

A well know italian car specialist who some of you may have heard me talking about has strongly advised against having a bailey or suchlike dumpvalve. He says without re-circ, the turbo will slow and therefore have a detrimental effect on your power as the turbo spins up again. Ok, seemed logical to me. but...

Lots of peeps on here have dump valves and I've not seen anyone complaining of reduced power, all the links on my searches are normally about fitting them the wrong way round

So my question is, why have one? I like the dump valve noise, anything to attract attention , but I don't want to do it for nothing. Give me you feedback guys!

You already have a dump valve fitted, a recirc type that makes little noise. The specialist is referring to the fact that the mixture runs ritch for a fraction of a second after "dumping" with the VTA or Whoosh type DV's. It makes no difference in reality. If you like the sound, go for a VTA, if you don't, stick with the bosch standard or if you like upgrade to a Forge recirc or suchlike.

I dont really see how that is possible. Correct me if i am wrong but both dump to atmosphere and re-circ dumps, are the same except one dumps to the atmosphere and one dumps the air back into the induction pipe?

If i'm correct here there there is no possible way that they would have different affects on the turbo. Both are dumping the same amount of air. If he is arguing that by dumping the air into the intake it is somehow 'reused' faster then thats just twoddle. With the amount of air rushing in there in the first place as you drive along, the small amount released by the dump valve would have absoloutly no effect (exept to possibly disrupt the intake airflow a tiny amount)

It does have an affect. The ECU is expecting a big dump of air into the intake, and dumps a load of fuel accordingly. If you are running a VTA obviously the fuel doesn't get in there and means that you run really rich for a millisecond! It really makes no odds though.

If you're dumping air into the induction, there are only two places for it to go.. either out through the filter or into the compressor blades.

With air passing through the compressor blades it helps keep the turbo spooled up.

Also some people get problems with the idle hunting for revs on tickover, even with a Twin-piston design, and perhaps the engine momentarily feeling a bit rough. I know CoupeDave gets this with his Blitz VTA DV.

But there is already air rushing in unless your at a standstill.

(not tring to argue just trying to understand the physics of how when u have air rushing into the intake at 'say' 50mph, the air coming out of the recirc dump valve suddenly makes a difference.

Pinin, I dont understand your ECU dumping fuel theory ?

For the dump valve to operate the throttle must be closed to create vacuum on the engine side of the throttle, if your off the throttle and the throttle is closed the engine isnt expecting any air at all so it shouldn't be injecting any fuel.

The idea of the re-circ is to keep the turbo spinning when the throttle is closed. When the throttle closes the turbo will still be spinning and creating pressure, without a dump valve this pressure would cause the turbo to stall as the pressurised air is trying to pass back through the turbo compressor.
The re-circ valve allows the air to pass from the high pressure side of the inlet back to the low pressure side and there for allows the turbo to keep spinning and in theory reduce lag.

Hmm, then perhaps I'm chatting runcorn. I'm no techie! This is just from what's been said on the forum in the past.

FWIW,

I'll pass on my experience from running my car for 4 years with a nice shiny red Bonalume DV (vent to air) the wrong way round (so basically running with no DV at all!).
On my standard car it made fcuk all difference
Did have the short ps-ps-ps sound but it was venting _in_ air bypassing the filter by the looks of it.

Put it right a week ago, the dv sound changed (one massive pssss) performancewise (still engine is normal) no dif.
At the moment I've removed the vacume tube out of it, but seems it's leaking boost (as I do hear a pss sound on lifting the foot of the gas) and I'm trying to find a suitable plug to remove it completely for some further testing.

I'm puzzled...

V.