dump valves on turbo cars

Trionic or pre? Does it use the combined coil and spark leads?

Pre-Trionic.

-- Mark.

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OK, you will already have a recirc dumpvalve fitted. You can fit a atmos valve, but you might find you black smoke. It may also stall if you rev it to dump at idle.

Benefits? Well it goes Pttsch obviously. Supposedly it stops the turbo stalling when the throttle closes. Your recirc valve does that anyway but quieter. If you replace the airbox with a cone filter or induction kit, and a 3rd party recirc valve with a spring/piston instead of diaphram, you will still hear it but quieter. The stock plastic valve can leak and make a squeak/moo/hoot noise If you replace it, fit a twin piston spring dump valve . An atmospheric valve will need a plug to block the route back. A recirc valve should fit straight back in place. Or you can get a Hybrid that combines both (partial plumbback/recirc and partial atmospheric, with adjustment between the two). Forge are popular for recirc or plumback.

Thanks for the info, I didn't know it had a recirc dump va;ve already, though i was driving it today (had to go get some parts for the jag) and notice there was no real lag after changing gear, the turbo was right there spinning. And best of all it doesn't go pttsch, which i consider a good thing. thanks again...

-- Mark.

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No worries. Will be black plastic and Shaped roughly like a T shape, with two fat pipe connections (25mm) and one small vacuum hose connection. Will vent back into the inlet between the turbo and the air filter box.

I can actually keep the turbo spun up between shifts, if you are quick, ratehr than the turbo freewheeling, and it can help fuel economy, if the car has an AFM/Mass Air meter.

It does do this, there is no suppose about it. I can prove this with datalogs from my car.. Quite intersting actually! Since the ecu fuel cuts on throttle close, I have no problems but the airflow log data shows a massive spike when the dump valve opens.

Ed

The air being recirculated has already been through the turbo and been heated, feeding it back through again just heats it up more. It's not going to make a huge difference on a normal road car running low boost but it's better to vent to atmosphere to allow cool air to be used.

Well spotted.

Absolute rubbish.

The car is set up by default to recirculate the air, dumping it introduces the possibility that of buggering up the fuel to air ratio - as air that was 'metered' for no longer exists in the system.

The air is not compressed when it is recirculated...

Your original post quoted "dump valves for turbo cars. benefits and drawbacks if you would please gents..." which makes no mention of an OEM dump valve or the type of FI system. Generally speaking it's always better to use cool air rather than re-use hot air which means dumping to atmosphere rather than recirculating. Whether the FI system is compatible with this or not is a different matter as not all meter the air.

Compress air = hot air = larger volume = less dense = less efficient - thus recirc ANY air that has been through a turbo once and you loose efficiency by: 1 the air has lost some of its density and two 2 the intercooler will have to cool air that is already warm before its entered the turbo for the second time to be only heated again. The air IS compressed to the point where the DV opens..

Wrong. Many cars totally cut off fuel when throttle is closed (the only time the DV will open). THIS ISNT what causes ecus to 'bugger up' that is caused by single piston dump valves that open at idle and allow unmetered air INTO the system causing it to run lean. This is why dual piston must be used on cars with airflow meters as they always remain closed at idle and all vacume conditions, this is even less of a proglem with ECUs that use MAP sensors for load readings, dump all the air you wont they will not give a damn.

Ed

But it gets hot by being compressed. Not by going thrrough the cold side of a turbo and "absorbing heat". Once it gets "dumped" it is uncompressed and goes cold again by the exact oposite method that heated it up. So it makes no difference other than that bit of air is a bit confused by now!

The only reason to do so is if you're under the misguided impression that dumping the air is somehow going to bring you a benefit.

Most people buy dump valves because they make a funny noise. People who buy them because they think they are going to get more cool air in their engines are idiots, and probably spend most of their time at Halfords and MaccyD's.

Which is why I said "introduces the possibility"...

It is then uncompressed and cools down again, aided by being mixed with normal intake air.

Doesn't matter if it's warmer, it's still far cooler than it's going to be when it goes through the turbo, and that is what counts.

At which point it is no longer compressed.

It obviously does, show me any evidence that shows reusing hot air is better than using cool air. On a normally aspirated or forced induction engine running at working temperature, the colder the induction air temperature is the better. Why would you think reusing hot air is better than using cold air?

The only evidence that makes it "obvious" that dumping to atmosphere is better is a simple snap judgement based on 'Halfords Physics' of "well it's colder innit !".

I never said it was "better", it's just no worse on normal roadgoing vehicles running standard boost.

But to notice a substantial difference you have to get into temperature drops heading towards or below zero - because then the difference between the intake temperature and the air which is suddenly being uncompressed and mixed with cold intake air (losing it's heat in the process) *is* large enough to make itself shown.

It does, it stops turbo stall for one. I have logs of my car with and without the dumpvalve operational, you can definately see an improvement with it in the logs...

So does a recirculating valve, that's pretty much the whole point of it being there. And anything that is half decent or 'recent' *did* come out of the factory with a recirc valve, so that benefit is something that only applies to old bangers.

Oops, Mk1 Micra alert... :)