Turbo question (BOVs)

[Benjamin]

Hi all,

I am looking for a decent answer to this question, so no trolling please

Why is it that some turbo setups, a-la Subaru WRX STi in WRC trim exhibit a "PRRRRT" on trailing throttle, whereas most Turbo setups I have heard on street cars have the same old poxy "PSSSSHHHT"?

I have also seen and heard high performance turboed cars which exhibit no BOV noise at all, apart from maybe a whoosh in the exhaust, which sounds ok.

I noticed that none of the the turbo gems (commisserations to Simon-StokTG I was fortunate to run with on the last big Melbourne cruise had pronounced BOV sounds considering their performance level

I don't mind the "PRRRT" sound, more purposeful, just wonderin what causes it.

Cheers

[Mr bayce]

I think you mean the sound an external wastegate makes

[rob_w]

i dont profess to know much about turbos, but in my experience, it all comes down to the type of BOV fitted....and wether it vents to the atmosphere[PSSSHHHHTT] or is a plumb-back system that vents to the air filter. or there is no BOV at all, and just wastegates as usual.
andrew beaton's lpg turbo BOV is kinda noisy......
rob.

[DR_GEM]

thats the sound of the (external in this case) wastegate, as the pressure bled off it is released. Most cars release the "pshhht" sound cos they have aftermarket bov's which are vented to atmosphere without altering the standard (internal) wastegate actuator on the turbo setup (ie. wrx's, 200sx's etc).
Also, it is possible to have the same effect of a bov using a passive blow back setup through the air filter pod to the turbo. This actually produces (in my general experience) a louder and smoother whoosh sound than a blow off valve, and on the mechanical side of things allows the boost pressure already in the pipes to be released naturally back through the inlet of the turbo as it continues to spool up off throttle.

hope i helped
cheers