Dump valve question

Well, most production cars with turbos don't have a dump valve, they have a waste gate.

No, but it might explain how you've heard on on a diesel!

No need to be a smartarse now! :-)

i'm sorry, but you are talking bollcoks even though you CAN fit a dump valve to a diesel engine, it's very expensive and not a lot of people bother a dump valve dumps the boost pressure when you lift off the throttle by way of using the vacuum produced by your engine to open the valve this releases any boost which could, in some cases, case the turbo to slow down it's spin rate due to the amount of air in the system "backing up" think of it as the release valve in a dam, too much pressure breaks things so releving a little when it's not needed helps

if you don't want the noise you can always go with a recirculating valve, but that just defeats the object in releasing the vented up air in the system, where does it go?

electronic, and they use the vacuum for the rbeaks to open the dump valve perhaps this is why he ran the red light when he found he couldn't stop?

Personally, I haven't actually heard a TD with a dump valve (electronic sound effect or actual dump valve wise) . However, I've mildly looked into TD tuning in the past and I know that such devices exist.

Heh, smartarse is my middle name. (c:

Douglas

" dojj" wrote in news:dd8i5i$gdp$ snipped-for-privacy@newsg1.svr.pol.co.uk:

Whoa! Hang on - I never said they were any good for diesels, was just pointing out that I worked with a lad, who was a boy racer, and he and all his mates with turbo diesels went through a trend of having dump valves fitted. Didn't do anything, as I'm well aware, they just thought the noise was cool.

" dojj" wrote in news:dd8i86$bfh$ snipped-for-privacy@newsg2.svr.pol.co.uk:

Nah, he'll have just run it because he's an idiot.

Are you sure? I was fairly confident that they do different things.

I thought waste gates are controlled by +ve pressure from the turbo, opening when boost reaches a certain level, and dump valves are controlled essentially by vacuum, created by the closing of the throttle?

Douglas

You will find most recentish Turbo's have a dump valve already fitted.Stalling the turbo when the throttle is snapped shut under boost doesnt do it much good, which is why it is there.

The reason you dont hear it, is cos they dump back to the airfilter or a pre turbo hose.

That said 99% of the nasty plastic Bosch type DV's are either already knackered and dont seal properly anyhow, and should be replaced asap.

The Bailey twin piston DV is about the only one that works properly with all management systems and can be ducted internally, should you wish.

Tim..

Actually some do, and are beginning to feature more and more now. As modern TD's are running pretty high boosts as standard now (the GM/ Fiat 1.9 150 runs 1.6bar stock, 1.8bar in overboost) stalling the compressor is dangerous and more so keeping lag down between gearchanges is more important.

Most of the GM 1.9, 2.2's, the Ford 2.2 155 ST, Volvo's D5 (in 185 spec) to name afew, are fitted with an inlet throttle valve and an integrated DV on the turbo.

Tim..

All current turbo petrols have a DV, alot of 'last seasons' do too, Saab were fitting them in the mid 80's! And yes you still need a wastegate or other means of controlling peak boost.

We do it with VCT turbo's now though.

Tim..

That's right. An excellent succinct explaination if I may say so.

Dump valves are fitted to reduce turbo lag. IOW to keep the turbo spinning as fast as possible, by allowing the boost pressure to escape when the throttle is closed.

Waste gates open to allow the exhaust gasses to bypass the turbo when the boost pressure reaches a certain level, to protect the engine.

I see no reason why dump valves should influence the life of a turbo either way. In a sense they don't affect affect it's normal operation. Mike.

my original post may have been a bit harsh :) sorry :) but they do the same thing for either engine so it's not as if it's going to not help but the speeds at which the turbos can stall is very high and i don't think a diesel will reach them sort of speeds for air flow and stuff

The boost doesn't make any difference - TDs don't have a throttle butterfly, so there is absolutely no need for a DV...

Some do, some dont, the increasing trend now is to *have* a throttle valve.

Tim..

Traditionally (before ecu's and such nonsense), the turbo wastegate purpose was to limit boost pressure (all turbos have them fitted in one form or another), and was controlled directly by the boost pressure. A dump valve was an additional valve, for performance reasons.

On modern cars, the turbo wastegate is often controlled by the ecu, and can be operated by either boost pressure or vacuum (vacuum being the most common). This has the benefit that with a little bit extra programming in the ecu, the wastegate can also serve the purpose off a dump valve.

They do have a slight gain, but not as much as a petrol engine. Although you don't have any throttle valve, when you do lift your foot off the accelrator, there is still pressure built up in the intake system, so fitting a dump valve will let the turbo spin for longer. On most modern diesels fitted with ECU controlled wastegates, they are quite often programmed to open the wastegate during deceleration, effectively acting as a dump valve.

Fair enough, although I've worked with a few turbo motors over the years

- Nissan, Volvo, Ford and Hyundai, not one of those has ever fitted a dump valve. Even the current batch of Honda TD's that I deal with do not have one AFAIK.