Quote:Originally posted by Tank:
Can someone explain to us what this does and how to.
Thanks,
TANK
Both a Blow Off Valve (BOV) and Bypass Valve (BPV) do the same thing (differences below).
When you are under boost and the turbo is spooled up, the exhaust turbine on the turbo is spun by the exhaust gases - this spins the compressor turbine - the compressor sucks air in from the air filter into the turbo inlet then out the compressor outlet - next the (compressed) air enters the Intercooler (if you have one) to cool the charge - next it enters the Throttle Body (assuming the throttle butterfly is open).
When you close the throttle butterfly (i.e. when shifting gears), the compressed air hits the closed butterfly valve and immediately reverses direction. This reversed air charge has no where to go but backwards into the spinning blades of the compressor turbine BAM ! This does two things...1) it immediately slows down the spinning of the turbine (reduces the spooling/spinning) and 2) reduced the life of the turbo since it's quite a rapid slap in the wrong direction. You can hear this happen each time you lift as a WHOOOOSH !
A BOV or BPV simply is a valve placed between the Compressor Outlet and the Throttle Body. When you lift, the system immediately reverts from boost (pressure) to vacuum. The BOV/BPV sees the vac and opens. When the air reverses at the butterfly it escapes backwards through the BOV/BPV instead of backwards into the turbo.
The difference between a BOV and a BPV is that a BOV vents the air to the atmosphere while the BPV vents the air back in front of the turbo. The BPV is necessary on systems that use a VAM or MAF since the air charge has already been metered into the system by the VAM/MAF. A BPV keeps this metered air in the system. If you used a BOV the metered air would escape the system and you would encounter a rich condition (same amout of fuel introduced by the system thinks that air is there...same fuel + less air = rich).
So, simply put...a BPV system is a hose placed between the Turbo compressor outlet and the Throttle body to the BPV - the BPV - a hose placed from the BPV to in front of the turbo to the compressor inlet elbow. And a vac line to the BPV from the Vac Tree.
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Dan Eaves
88TC 5spd, Crower 5.5" Sportsman Rods, Short Wiseco Pistons bored .030" Over, Ported Head with Polished Combustion Chambers, Gutted & Polished Upper, Ported & Polished Lower, Polished T/B, Ported E6, SVO T3 .63AR Turbo, Bosch Bypass Valve, 3" DP w/No Cat, 2 1/2" DynoMax single cat back w/DynoMax Super Turbo Muffler, RR Cam, K&N in Fenderwell, Gillis Boost Valve, Centerforce I Clutch, Removed A/C, Polished Wheels, Polished Valve Cover, Polished Crank and W/P Pulleys, Walbro 255LPH HP Pump, Kirban Adj FPR, and the DAMN Heater Core is new too !
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[This message has been edited by Dan E (edited 07-04-2002).]
