StickyMicky

just heard a escort cossie flying round a skind pan and the waste gate was going nuts

why is this exacytly?
is this due to large amounts of boost and a recirc dump valve??

StickyMicky

hmmm after sum more research on this site

ive read that if u remove the dumpvalve compleatly and block the wholes the car will chatter
and it makes it faster through the gears!?!?
how is this possible, surely the air will stall the turbo making it take longer to build up momentum again

i relise this will damage the turbo over time

any thoughts??

RB5-Black

I'm no expert so I may be shot down in flames here

The Dump valve is there to release the pressure from the system when off throttle. This makes gear changes quicker because the Impeller will spin free in zero pressure, so when you go back on throttle the turbo can spin up faster.

That and you shouldn't dead head a centrifugal comp as the heat generated will be huge.

[Flame suit on] Craig [/flame suit off]

Turbo_Steve

Well, this was a long running debate on here a while back and I don't think a definite conclusion has been come to: Several people have without a dumpvalve which (although shortens the life of the turbo) improves the driveability of the car. Apparently.

I found mine got quicker between gears with a VTA fitted, so go figure. It's against all logic.


The chatter you heard was more likely to be dumpvalve chatter than wastegate chatter, as he backed on and off the throttle. Wastegates tend to "squeak" rather than chatter. If it sounded like a WRC car it was wastegate chatter (WRC cars do not run dumpvalves) but if it sounded a lot more like air being released then chances are the cossie was running a strong spring in his dumpvalve. This means the valve needs more boost to open, and less to snap shut, which means (as the turbo is still spinning when it snaps shut) a little more pressure is generated and the valve opens again, releases some more, closes, compresses, releases some more....etc etc until turbo has slowed significantly. There are those that argue that this "chatter" can cause damage to the turbo too, but as it would happen over a LONG period of time, there is no conclusive proof.

If the dumpvalve sounded quite muffled, it is because it was a re-circulating type, so the sound was heard through the airfilter.

It's quite a cool noise

Hope this info helps.
Critiscism welcome!

Scott.T

iTrader: (2)

I ran my old 3-Door cosworth with the dump valve blanked off, and this gave a very nice chatter sound.

I've not yet done it to my Subaru, but the theory that it shortenes the life of the Turbo is probably correct although I suspect it is minimal, as many Turbo cars in the 80's didn't even run a dump valve.

It's only in later years that manufacurer's have been fitting re-circulating and boy booters have been fitting VTA's to their Escorts, Renualt and Uno Turbo's

silver:scooby

The sound you hear when ruuning with out a dump valve is not wastgate chatter or dump valve chatter, When on boost and shut the throttle you have got a lot of boost stuck so what happens is the air try's to escape back thought the turbo, causing turbo stall and if you run alot of boost pressure you can shatter the turbo blades.
Scott t, cossies came out of the factory with dump valves back in the 80s the reson they did not fit them to the cars you said is they only run about 8psi of boost. If you speak to any good tuner in the motor sport world like atfords, paul bailey, scotty from A1 motor sport who build and run 400bhp+ cossies on a daily bases would tell you same.


[Edited by silver:scooby - 4/21/2003 10:19:31 AM]

Turbo_Steve

silver:Scooby all the cars I have heard without dumpvalves "squeak" rather than chatter? I'm not saying I'm right, just explaining my explanation (???)

I could believe the compressor wheel could shatter, but the photos I have seen of a turbo repeatedly stalled at high boost depicted the edges of the blades all worn away after 20,000 miles.
Apparently this is more of a problem on the IHI's than the Mitsubishi' turbos. This is all rumour and heresay, though!

Disco

Micky, I run a Forge recirc valve with a shim and a very stiff spring. Its so stiff that basically unless I back off fully it doesn't open and you get a fantastic wastegate chatter. You get WRC style frantic chatter in lower gears and something more akin to a horse in higher gears......top stuff!!!

Turbo_Steve

erp....not doing a lot for your turbo's life span, though

StickyMicky

this cossie defo sounds the same as a rally car
with the fluttery sound

so it helps performance but kills the turbo
not really worth doing then is it

Turbo_Steve

Kills it slowly, though.

You could always fit a solenoid in the vacuum line of your dumpvalve. Then you could switch it on and off from the dashboard. Easy enough to do, cost about £35. Run with it normal most of the time, and just switch the dumpvalve off when you want mega mega performance.

Or something along those lines.

Leslie

A long time ago I installed an turbo on a 1300 cc Ford BDA engine. This was in the very early days when Renault were achieving some success with their Turbo F1 car. There was no knowledge except for a book about it which I think was American. This at least showed how to calculate the turbo wheel you needed for a given mass flow of air. The fueling was with Lucas mechanical fuel injection. The fuel was metered by a shuttle which had its stroke controlled by the throttle opening. Difficult to control for mass air flow from the turbo as it wound up. One question for Turbo Steve. I thought the "vacuum" line to the dump valve carried pressure from the inlet manifold to keep the dump valve shut during boost up. Am I right in thinking that if you blocked that line with a solenoid valve the dump valve would not remain shut and you would get no boost. Maybe it carries vacuum as well to help it to open too.

Dump valves had not been heard of then and I had to make a boost controlled wastegate with a large diesel exhaust valve and a diaphram made out of a Ford vacuum pump(windscreen wipers!)

I was using 20 psi and getting about 275 BHP. The first time I tried it at Brands, I wound it up along the top straight, it was pretty impressive since the car weighed 850 pounds. When I took my foot off to brake the car would not slow down since the inertia in the turbo was still forcing air past the throttle slides! It was lucky I had very good AR brakes and just managed to make it round Paddock Bend, the wheels were locked for quite a while!

I then had to invent a dump valve out of a brake master cylinder with a mechanical linkage to the throttle. The car was then driveable because not only did it slow down, but also the turbo was still spinning fast when I opened the throttle again on the way out of the corner, turbo lag was vastly reduced.

I cant quite see the advantage of no dump valve for extra performance, would be grateful if someone would explain why. Also I wonder if the noise called waste gate chatter is really caused by the turbo impellorstalling as the throttle is closed. That is what will eventually cause turbo failure and also serious engine damage as the broken impellorblades are sucked into the engine. The waste gate is on the exhaust side of the turbo and I dont see how the dump valve will affect it.

Interested in the answers to all this from the experts.

Les

[Edited by Leslie - 5/21/2003 12:18:47 PM]

RB5_245

The HKS SSQV is held shut by a spring, and the boost pressure, so dissconnecting the hose leaves it shut all the time. Yesterday i did some playing and found no difference in lag between the SSQV and no dump v/v in fact if you get off and on the trottle in the same gear without the dump v/v it's better. Strangely both methods are better than the standard v/v. so it must be on there originally to protect the turbo.

This was done at stock boost with a TD04. I'm leaving the dump v/v shut from now on, but i'm getting a new turbo anyway.

Leslie

That clears up my misconception. The vacuum in the manifold when the throttle is closed must suck the dump valve to the open position. Thanks for the explanation RB5.

Les

Turbo_Steve

Yup. The HKS SQV is triggered by a pressure differential between the inlet manifold and the intercooler feed.

Oddly enough, I agree with RB5, no dumpvalve and HKS SQV seem to have almost identical responses, but both are WAY better than the factory item (which IMO is a bag of pants...I have had two, and both seemed to leak badly)

Even weirder is that after fitting the dumpvalve, the gearshift felt "quicker" somehow....though I cannot see a single mechanical reson why this should be. But the VTA dumpvalve definitely shaved .4 off my 0-100mph time. And although I know a VTA has a potential for piston/bore wash, I can't see it being THAT much of a risk, and I LOVE the sound. Sad, but hey, I drive a legacy.

As for you, Leslie, YOU sound like a man who is pretty dangerous around a welder . Nice to have a pioneer on board.....any pics of your past achievements?

Leslie

I'll see if I can find a picture somewhere T_Steve. It was all good fun and an interesting period for me. I had already spent a long time trying to get the most out of normally aspirated engines.

I have a VTA dump valve and have also driven a UK model with the standard recirc. dump valve. I noticed a lag in the rpm drop immediately on the recirc version and it did delay the change up just a fraction. When I first drove mine I thought all the valves had fallen on the floor when the VTA dumped the boost, but I have got used to it and would not change it now. I think maybe the recirc type keeps the rpm up for just a fraction by dumping the excess boost back into the inlet even if it is on the other side of the throttle valve. Just like my problem all that time ago.

Les

Turbo_Steve

My suspicion is that it mildly pressurises the crank case when you re-circ: the Recirc inlet is RIGHT next to the re-breathing outlet, and I cannot help but wonder if that could cause it. But that is completely a guess.

And probably drivel.

ChristianR

iTrader: (1)

re dumpvalves, see here: http://www.scoobynet.co.uk/bbs/threa...hreadID=211629

RB5_245

I'm Glad people agreed with me coz one tuner i spoke to said they made no difference and i only felt it coz i'd spent so much money on it, same with the hks indution kit. I'm not going back there!