if you hate the noise and want it as quiet as possible, you'll need to recirc. Given that, and that you'll be running low boost, you could consider a cossie / vw standard recirc valve - I used to run one on my R5GTT. Almost silent (well, as quiet as you'll ever get).

http://www.ebay.co.uk/itm/SAAB-44418...c#ht_918wt_905

nice!! now thats good know :)

So this argument is basically a trade off of either:

keep the inlet pressurised but take a hit in turbine rpm - a la no DV
de pressurise inlet & maintain higher turbinerpm - a la DV

Would the individual turbo not also play a big part, larger slower spooling turbo would see more benefit to maintaining its rpm, compared to a turbo which can spool quickly & might lend itself more to maintaining pressure?

What about if you are at full boost/high rpm & just close the throttle to engine brake without a DV, surely that wouldn't be good?

Yes - but really there is no benefit from keeping pressure in the inlet. You risk damage to the turbo, and the very pressure you're trying to keep is working against you to slow the rotation of the compressor wheel.

Absolutely. That's a very good thought.

However, remember that the larger turbo has more mass in it's rotating assembly (compressor and turbine wheels), and therefore more inertia - so the "bad" pressure on throttle closure has less effect on stalling the compressor wheel. I think it would even out somewhat, but it's something I didn't think about actually!

Yes - that's the worst case situation for the turbo - maximum boost pressure, maximum turbo rpm (perhaps 100,000 rpm+) and then TB closure. That would be the point where you'd have the most stress on the compressor wheel and front side bearing.

Mmm, it may all just be relative actually, the larger turbo will probably be giving higher compression anyway so a greater force back onto the turbine, despite the larger inertia i imagine it would be somewhat similar to the small turbine/low boost.

Good food for though though, good thread!

My dumps tend to recirculate, stinky ones too, tis annoying!

Wow just seen all this. Ross bieng his typical self in that his way is the only way everyone else is wrong.

At the end of the day its down to personal preference, how you want the car to act and sound. There are way to many variables to simply say no DV-loads of lag, DV-no lag... I'd be much more bothered about the spec/build/map of the engine.

BUT what i can't stand is people banging on about it damaging your turbo, none of the big power cars round here run dump valves, I don't my mates 500bhp+ astra doesn't, a 700bhp scooby doesn't... All without problem. The internet breeds rumours like this and everyone gets scared. :homme:

The worst that will happen there is damaging your inlet. I do this with 1.2-1.4 all the time and it has never caused me any problems, on a turbo with millions of miles on already.

Yeah. screw Garrett. What do they know. :p

On 8psi it shouldn't cause any lag at all. And it won't damage your turbo.

They know nothing...

Quite :p

just realised you got same email. it says it doesnt effect lag to me though.

stupid computer

3 fooking posts!!

you have missed the part off your email which says that it has NO effect on lag. edited perhaps?

here is the unedited version

Subject: RE: dump Valve
Date: Mon, 22 Aug 2011 08:30:31 -0700
From: GarrettGearhead@Honeywell.com
To: williamsperformance@live.com

Hello Marc,



I’m not sure what you mean by “dump valve,” so I’ll address my best hypothesis which is that it is a blow off valve.



If this is what it means, then I highly recommend using one in order to reduce the occurrence of surge in the turbo and significantly increase the life of the turbo.



Neither of these greatly effects the lag of the turbo. Proper turbo matching, tuning and a host of other things does, but control devices such as blow off valves and wastegates aren’t going change the transient response that much and should absolutely be used on gasoline engines.



I will tell the person with whom you seem to be having this discussion the same thing.



Regards,



Garrett Gearhead

for people that want to see what garret actually replied.

is there a reason you edited this out your email? he must of said that to you as your email after that was regarding that paragraph about transient response?

I did email them twice (as I posted). Did you specifically request they clarify the exact situation as I did? Thats why I got a second reply.

Well, lets put this to bed shall we! I suspect the debate will continue far longer than either of us care to worry about it - not just on this forum, but also elsewhere judging by how much discussion there is on the subject!

What we can take from this Marc is that the situation is unclear. I was very sure of my position (and still am obviously!), but your email from Garrett, although similar to mine, implies there is no difference in response. I apologise for being so strong-willed with my opinion. :) What we can deduce from this is that it seems even those who should know the answer don't.

Unfortunately, we're still no clearer ourselves! Perhaps the way to settle this is to test it back-to-back on a dyno somehow. We should be able to perform a series of tests with a dump valve whilst logging data and see the results, then overlay the data from running without the dump valve. I would guess that's the only real way now!

Did you fancy organising something? I'll be next on the dyno on the 6th September. I can do some runs then if you'd like? You're welcome to come along. Or if you're on the dyno before then. I can come to you? Should make for an interesting time :)

Thanks for such a good debate Marc - it's still not settled, but at least we're clear that there IS no clear answer!

thats the only way to find out. thats what i have been trying to tell you though, the person i was talking to about it had already done the tests and showed it made full boost 0.2s quicker without DV.

mine wont be back on the road for a while so your best trying it with your car next month.

I'd love to see the results to see what sort of difference it made, with and without