the compressed air goes back through the compressor between the blades and the housing, i kow theres not much room but thats where it goes.

we'll just agree to disagree. i'll not worry about your engine you dont worry about mine,

I'm not worried about your car (nor mine that much to be fair!) - I was replying originally because I don't like to see misinformation on a subject that could end up actually damaging someone's engine if heeded.

I'm still waiting for you to link to where lag is reduced by NOT running a dump valve. :)

ive posted it about 5 times. the car made 1.8 bar after a gear change 0.2s quicker without a DV.

According to one of your "mates" who you claim works at garrett. You've provided no link or documentation to back up this claim.

However, garrett disagree. As does the rest of the industry. As per the links I posted, I've backed up everything I've claimed with major players documentation.

I'm still waiting for your links. :)

he isnt a mate, it was a private conversion so its pretty hard to provide a link to that,

So in essence, one guy you know said something to you that you've taken as gospel truth.

The entire turbo industry disagrees (with which I've backed up from all major players, garrett, turbo dynamics, turbosmart, hks, greddy, grahame goode etc).

Don't you think that's a little bizarre? "The whole world is wrong, and I'm right because one person told me something". Are you honestly that naive?

only one of your qoutes say they reduce lag, turbo technics say they are SOMETIMES required on boost above 1 bar, and the rest explain what DV's do. i had come to that conlcusion before i spoke to this person. and from the test he done showed me it made boost quicker.

i'll be honest. i got it all from max power mag.

Just to clear this up one LAST time, here's what Garrett say on the subject:
http://www.turbobygarrett.com/turbob...r/faqs.html#t3

So - we've established NOT running a dump valve causes surge or compressor stall (dictated by the amount of pressure built up in the intake system).

Given that...

So - we can see a direct correlation between the compressor stalling and lag.

Is that clear enough?

but you already have boost pressure built up in the intake. your starting with postive pressure as opposed to atmospheric.

Agreed. And that positive pressure is effectively trying to turn your compressor wheel the wrong way as the shut TB is forcing air to go back into the compressor housing it's just come out of.

Lets say the turbo is spinning at 50,000 rpm whilst making boost. In your example, the turbo is forced to slow to perhaps 5,000 rpm because of the back pressure on the compressor wheel trying to force the blades the wrong way as the air has to go somewhere - obviously it's losing inertia slowing down like this. With a dump valve, the boost is allowed to escape the intake system, meaning the compressor is NOT slowed down by the air being forced back on it, and it is allowed to continue spinning with it's own momentum, perhaps retaining 80% of it's inertia. The time taken to recover the RPM from this near stall is FAR higher than the time taken the recover from a 20% loss.
(I've plucked these numbers of of the air but just to highlight the examples).

If we look on wikipedia for example:
http://en.wikipedia.org/wiki/Turboch...low_off_valves
Ever heard of Guy Croft? Engine building legend? Here's his personal take on it:

Don't mean to take away from your debate gents. To the OP, I have personally found that the Bosch brand valve is very quiet, nearly silent. Also, have you thought of going with a dual port valve? Best of both worlds, recirculating and atmospheric. Most of the dual ports you can convert to a full atmospheric or full bypass using a plug(which they supply). Just my 2 cents

love it its like verbal tennis :boxing:

I'm just not sure how someone can continue to disagree in the face of total overwhelming evidence to the contrary. I've posted links from industry experts, engine builders, suppliers, tuners and even turbo manufacturers themselves, and yet here we are, still disagreeing. All because one person had a conversation about it. I don't understand. Hell - I hate being wrong, but when faced with the evidence as strong as this, even I would concede ;)

Loving the debate I personally don't know bugger all about turbo stall so I'll keep myself to myself. From reading most of the posts i feel like im getting more inteligent. :clapping: What I want to know is if I remove my dump valve. Will I get the famous flutter noise? If so, anyone want a Bailey dump valve lol.

Yes you will. And it costs nothing. Right up until your turbo fails :p... You'll also loose response on gearchanges - exactly what the discussion is about :p

hopefully will see something different come out of this in the next few weeks

On 8psi though Ross? Will I notice any lag? Will it damage my turbo quickly?

Cheers for the help mate.:y:

So anyway - to clear this up, as William said he spoke to someone who worked at Garrett, I emailed Garrett this AM, and have now got a reply. Here's what they say when asked the direct question about damage and spool up time.

Here's my email to them:

And their reply:
I replied:
and finally, their reply:
Hopefully that settles it :)

dam you! I have to budget for a poo valve aswell now lol! oh well no harm done

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