JKJ2

Been working nights recently allowing lots of time to read motoring mags. CCC covered the various dump valves available, and was just wondering if anyone was running the recirculating type vs the std diaphragm, apparently the recycling of the boost pressure not only keeps the turbo spinning but may add to the longevity of the unit. Any comments ?

EvoRSX

JKJ2,
The Evo runs a recirculating dump valve as standard, as do most other turbo cars and these are fitted purely to reduce the noise created by a vent to atmosphere (VTA) valve or the noise of the compressor stalling when a dump valve isn't fitted.
Recirc valves are a lot quieter than VTA valves.

The thing about a recirc valve keeping the turbo spinning is a bit bizarre because if you think about it, the turbo is spun by the exhaust gases passing through the turbine and when the throttle is closed the exhasut gas flow is drastically reduced and so the turbo slows down and passing air back into the intake won't do anything to speed up the turbo.

What the dump valve (both types) does is it stops a reverse pressure pulse from passing back down the intake system and causing the compressor wheel to stall or spin in reverse. If this happens then the air can also pass backwards through the airflow meter and cause problems with incorrect readings. It is the stopping of this reverse pressure pulse that will increase the life of the turbo and this can be achieved by fitting either type of dump valve.

Hope this helps

Andy