Discussion
they vent the boost pressure when you lift off suddenly. when you slam the throttle shut, the turbo is still making a lot of boost. this backs up and makes the turbo stop very quickly.
it basically vents this excess pressure so the turbo is still making boost when you come back on the throttle. it is also supposed to improve turbo life.
Plus it sounds cool
>> Edited by chief-0369 on Wednesday 17th December 16:37
it basically vents this excess pressure so the turbo is still making boost when you come back on the throttle. it is also supposed to improve turbo life.
Plus it sounds cool
>> Edited by chief-0369 on Wednesday 17th December 16:37
the dump valve releases air pressure, when you decelerate the engine from high boost, they are added to protect the inlet turbine from too much back pressure in high boost engines, but some add them for a whoosh sound, but if it releases too much the turbo will slow down very quickly and cause a lag if you come back on throttle very quickly.
Most factory turbo cars have them as standard, for at least 15 years. Bosch make a plastic one, it costs about £15. Most factory ones are recirculating.
They don't make your car go faster, you can produce faster gear changes by simply not fully lifing off during a change. This keeps the boost pressure up and reduces lag.
They do sound good & the boys like em, good for frightening numpties too.
They don't make your car go faster, you can produce faster gear changes by simply not fully lifing off during a change. This keeps the boost pressure up and reduces lag.
They do sound good & the boys like em, good for frightening numpties too.
agent006 said:
... and if you don't think it sounds cool you can get a "recirculating dump valve" that dumps excess boost into the air intake, thus eliminating the sound whilst keeping the benfit.
and making it pop and bang and splutter. What more could you want?
Why would think a recirculating DV would make the car pop, bang and splutter any more than a DTA valve?
If the car measures air flow into the engine using an air flow meter or similar device then venting boost to the atmosphere will confuse the ECU and it'll add more fuel to go with the air that it thinks is being used by the engine.
Venting the boost back into the air box or the air intake keeps the ECU happy but doesn't make much of a noise.
A useful modification is to move the DV to as close to the throttle body as possible, on the cold side of the intercooler. Some manufacturers put them on the hot side, right after the turbo, so it'll be venting very hot air back into the intake to be heated again by the turbo. On the cold side it'll be venting cooler air and also the intercooler with remain at a slightly higher pressure so when you get back on the accelerator there's less lag.
Venting the boost back into the air box or the air intake keeps the ECU happy but doesn't make much of a noise.
A useful modification is to move the DV to as close to the throttle body as possible, on the cold side of the intercooler. Some manufacturers put them on the hot side, right after the turbo, so it'll be venting very hot air back into the intake to be heated again by the turbo. On the cold side it'll be venting cooler air and also the intercooler with remain at a slightly higher pressure so when you get back on the accelerator there's less lag.
As busa rush has correctly said, the best place, and the only correct place for a DV is right before the throttle plate.
The reason being not only one of cooled air being recirculated back to intake, but also for the following reason.
If the DV is BEFORE the cooler then as the throttle is released, vacuum gets applied to the diaphragm(as usual) which lifts the piston off its seat along with help from the boost pressure.
The scenario is that the intake tract all the way up to the throttle valve is pressurised.
As soon as the piston lifts, youll get a flow reversal of the pressurised air trapped in the cooler. Very bad for flow.
If the DV is positioned directly in front of the throttle valve, itll simply vent the excess pressure in the optimum direction with no nasty flow reversals.
The reason being not only one of cooled air being recirculated back to intake, but also for the following reason.
If the DV is BEFORE the cooler then as the throttle is released, vacuum gets applied to the diaphragm(as usual) which lifts the piston off its seat along with help from the boost pressure.
The scenario is that the intake tract all the way up to the throttle valve is pressurised.
As soon as the piston lifts, youll get a flow reversal of the pressurised air trapped in the cooler. Very bad for flow.
If the DV is positioned directly in front of the throttle valve, itll simply vent the excess pressure in the optimum direction with no nasty flow reversals.
busa_rush said:
If the car measures air flow into the engine using an air flow meter or similar device then venting boost to the atmosphere will confuse the ECU and it'll add more fuel to go with the air that it thinks is being used by the engine.
Venting the boost back into the air box or the air intake keeps the ECU happy but doesn't make much of a noise.
Right, which is why I was questioning why the use of a recirculating DV would have such undesirable effects as Agent006 was saying.
The worst aspect of the recirculating valve is that the air has already been compressed, and therefore heated, so when the throttle is opened the engine will briefly inhale a hotter than usual charge.
To stir the pot.....
I must add that after 7years of running a dump valve on my cossie with 25psi..... I was advised to remove it by Ahmed (top cossie tuner) and now don't run one.
The reason is that the gain by keeping the turbo spinning is thought by some to be less than the losses from back pressure slowing the turbo i.e. can actually be detrimental to response.
Therefore it was reasoned that the only reason for fitting the dump valve went back to protection of the turbo which is only neccessary on very large T4+ due to the ratio of the blade to shaft size, thus my mear T3.4 wasn't a problem.
Must say I was very sceptical when he told me but 2years later I've had no problems but I can't really say I can notice any difference.
For me after 7yrs the noise was a bit embarasing, although you'd be surprised how much noise the turbo and wastegate make on boost anyhow.
Andy
I must add that after 7years of running a dump valve on my cossie with 25psi..... I was advised to remove it by Ahmed (top cossie tuner) and now don't run one.
The reason is that the gain by keeping the turbo spinning is thought by some to be less than the losses from back pressure slowing the turbo i.e. can actually be detrimental to response.
Therefore it was reasoned that the only reason for fitting the dump valve went back to protection of the turbo which is only neccessary on very large T4+ due to the ratio of the blade to shaft size, thus my mear T3.4 wasn't a problem.
Must say I was very sceptical when he told me but 2years later I've had no problems but I can't really say I can notice any difference.
For me after 7yrs the noise was a bit embarasing, although you'd be surprised how much noise the turbo and wastegate make on boost anyhow.
Andy
Mr2Mike said:
Right, which is why I was questioning why the use of a recirculating DV would have such undesirable effects as Agent006 was saying.
Whoever said it was undesireable?!!
Just commenting on what people have told me about fitting a recirc valve to car that is supposed to have an open one.
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