Dump valve v. turbo chatter
Turbo Mini Forums

I have tried two different (S/H) dump valves but got so pissed off with the constant hissing on every gearchange and every time I lifted off I removed them. I ,perhaps naively,thought that what I would get would be one short sharp hiss instead of the long sound that I got. I now run with a good deal of chirping from the compressor and am getting concerned that this will, long term, cause damage from what I have read on the forum.Having recently fitted a new T31 actuator with about 3mm preload the chirping is even more pronounced (running about 12 psi,but it is not stable, and I get a lot of "coughing" on WTO)
Should I go back to a dump valve to protect the turbo?
Does the lack of a dump valve have any bearing on the "coughing"?.
I am using a plenum with a stronger spring on the blow off valve and this does not seem to be lifting,so does not seem to be an issue.All comments welcome (and I have searched)

You can get an adjustable DV or recirculating type.

If not, get one of the Forge ones with the filter. This is what I use and it is a lot quieter.

I personally wouldn't run without one.

In the 13's at last!.. Just

A recirculating one is my prefered solution - it's what the average turbo car from the factory uses and they are dirt cheap on eBay because the boy racers take them off to replace them with the noisy atmospheric ones !!!

Or your local scrappy.

The Bosch plastic one is most common.

As above, I wouldn't run without one, you are effectively stalling the compressor from a very high speed.

Re. the plenum relief (blow off) valve, if you don't have a dump valve, that is the only protection the compressor has so, if anything, you want a standard or weaker spring.

EDIT -

like this....

http://cgi.ebay.co.uk/Saab-2-0t-2-3T-Aero-...A1%7C240%3A1318

Edited by Rod S on 5th Nov, 2008.

Schrödinger's cat - so which one am I ???

I ran mine without one and im sure it contributed to my turbo letting go. For piece of mind I would fit one mate.

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1/4mile in 13.2sec @ 111 terminal on 15psi

i thought that the cherping was the wastegate, opening and closing quickly? if so doesnt that just mean your actuator is working well if its cherping?

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-Rover 100 VVC #2 - track project

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Pardon my ignorance(again)but do I assume that with a recirculating valve I dump the pressure back into the inlet to the turbo compressor housing, or the aircleaner housing ?.Many thanks to all for the guidance.Does anyone have a comment on the "coughing" please ?.

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1/4mile in 13.2sec @ 111 terminal on 15psi

paul, the chirping that you hear is the compressor stalling/"cutting" through the air that is being basically thrown back it.

i am pretty sure that the recirc does go back to the filter side of the turbo yes.

For a recirculating dump valve, on a typical "factory fit" it will relieve from immediately after the compressor (before any intercooler) and dump back to the compressor inlet (ie, between the air filter and the compressor).

So you require an additional Tee in the hose between air filter and compressor.

They are still actuated from a vacuum signal line from the inlet manifold (ie, after the throttle plate).

The noise - I could only guess as my current daily runs a recirculating dump valve so I don't have the compressor stalling.

It might be noise from the compressor stalling, it might be from the wastegate as it opens fast to respond to a large pressure spike as the throttle plate shuts and no dump valve to avoid the spike ???

Whatever, from your description, it doesn't sound good.

On my daily, with a nice quiet recirculating dump valve, all I hear on every gearchange (under boost) is a short subdued "squeal" from the wastegate as it closes fast to try and regain the air pressure that is now being dumped.

I hope I can replicate it on the Mini project as that T3 is now on 120k (hard) miles without any problem.

Edited by Rod S on 5th Nov, 2008.

Schrödinger's cat - so which one am I ???

By 'Coughing' do you mean that it's misfiring?

If so, you need to get it set up. Has it been on the rollers?

In the 13's at last!.. Just

I keep learning on this forum -its great !
Yes lizard its cutting out for fractions of a second at a time as soon as the boost comes up on WOT.I can minimise it by applying throttle steadily and slowly increasing boost (which rather defeats the object of the whole thing( but it will eventually start the coughing.Matty I tried Lemsip, but it made it hard to start and the exhaust smelled funny.
I know that it must go on the rollers eventually, but what I am trying to do is work out lots of these probs on the present donkey engine in there prior to fitting the new one with all the good bits on it so that I have a fighting chance of getting it both on and off the rollers in one piece.(the present engine is down to 30lbs oil pressure hot and I dont want to fry it on the rollers just yet.)Thanks again to everyone who has offered helpful suggestions.

You will fry it more quickly if you don't get it on the rollers.

Sounds just like what I had with mine when it was leaning off with the part throttle lean off pipe connected.

Luckily I was running a just 7psi and stopped driving it when it developed the problem. If you are hooning around with 12psi up its arse, you will be looking at fitting that new engine sooner than you planned!

Edited by theoneeyedlizard on 5th Nov, 2008.

In the 13's at last!.. Just

I have noted your graphic warning !!

Mine used to do something that I would discribe as coughing and it was the overboost spring thing opening and leaking

Either block it off, or pack it out with some 5p's

Id also definately put a dumpvalve on there of some sort, I ran with one for a year and the turbo was fine, then I ran without and the turbo went very wobbly within a few months

Hi,
I'd recommend the Forge Group A D/V with a filter. You can by a tuning kit for £10 which comes with different springs and shims to tune it to how you want it.
Cheers,
Gavin :)

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Again, sharing views like this is so valuable to someone who is still low down on the turbo learning curve. Thinking about it some more I feel sure that I have been too quick to apply more boost without working out all the implications. Back to the (metaphorical)drawing board.

I have now fitted a recirculating dump valve (the actual one that Rod S suggested from Ebay) and plumbed the outlet from it back to the large airfilter housing that I have at the front of the car.It hisses louder than the previous atmospheric dump valves !!.I have cured the coughing by reinstalling the M/t electronic dizzy and a set of harder plugs.It is now quite alarmingly rapid on 10lbs and when I flick the switch to open the bleed valve giving 15 lbs it goes mental.The lean off connections for part throttle have always been blanked off - I am rarely on part throttle.I have also replaced the original spring on the M/t plenum blow off valve - could it be that that is hissing I wonder ?. Will change it back to the stronger spring tomoorow and try again.BTW the met someone recently with a Morris Minor running a Marina 1.3 engine with just the standard M/T manifolds etc and a small intercooler and he was running 15lbs all the time - standard pistons,head,valves etc and says he has done it for over 12 months with no probs.Food for thought ?.

Schrödinger's cat - so which one am I ???

Fully understand the bit about the crude blow off valve so I will probably blank it off (again) Not so sure why the dump valve return has to be so close to the compressor inlet (its all a bit crowded down there) Im presently dumping into a fabricated alloy air filter box containing a large oval K and N.Lets see what happens after I have done the blanking off bit.Other than the irritating noise its going the best its ever done,so some progress, I suppose.

Schrödinger's cat - so which one am I ???

Pipe it into the exhaust manifold. Cue very rude popping and banging. You would look like a right nob, but really, secretly, it would be quite cool

Bugger off, I'm getting there.

except for part throttle when the engine will be sucking in exhaust gasses....

On 20th Nov, 2008 Hedgemonkey said:
Pipe it into the exhaust manifold. Cue very rude popping and banging. You would look like a right nob, but really, secretly, it would be quite cool

non return valve?

I am also joking....but I bet some monkeys have done it

Edited by Hedgemonkey on 20th Nov, 2008.

Bugger off, I'm getting there.

Dont think I,m not grateful, but I dont need any help to make an arse of myself.Just did my back in working on the car so progress will be suspended for a while.

Forced myself back into the workshop today as I was keen to see the result of the present alterations.Wish I had read properly and listened to Rod S in the first place as now that the dump valve is plumbed into the hose from the aircleaner to compressor inlet the hiss is much reduced and now acceptable.At least it doesnt turn heads anymore.To get things to fit I have had to put the dump valve in the pipe from the intercooler to the plenum.The engine bay looks abit of a mess for pipes and junctions now but it WORKS !Readjusted "normal" boost to 10lbs with a bleed valve operated from a Metro anti run on valve to give 15 lbs at the flick of a switch.-but only for short bursts.Time now for the new engine with the right cam and a decent head,hopefully before Christmas so that I can get it re tuned and fully ready for the spring.