I came across this vid on youtube yesterday of a procharged s197 that had some aftermarket blow off valve, and it sounded NASTY!!! It had a really loud flutter to it. Kind of sounded like a really pissed off turkey! Any ideas as to what bov it could've been? I've been searching to try and find sound clips/vids of different procharger bov's but haven't been able to find anything like I heard on that car.
It doesn't make sense at all if you know what a blow off valve does and why turbos use it. A belt driven Centri will not slow down or stall
and there is no lag.
-------
When the throttle plate on a turbocharged engine closes, the high pressure air in the intake system is trapped by the throttle and a pressure wave is forced back into the compressor. The compressor wheel slows rapidly and may even stall, and the driver will notice a fluttering air sound. The rapid slowing or stalling stresses the turbo and imparts severe turbo lag if the driver accelerates immediately after the surge event.
__________________
Xcharger with water injection, JBA headers
JBA duals with an H pipe, Roush rear springs, Che K member brace with torque limiters, Cervini's quarter window deletes, Canton polished expansion tank, Roush scoop, Street Scene Elenor grille, custom GT500 chin spoiler, PJ rear louvers, Black rear spoiler, BSM custom stripes, Hurst shifter, Billet interior trim, custom door welts, Autometer dash pod, AEM wideband, Autometer boost & Fuel pressure gauges
Call me crazy... but procharger definately sells an upgrade bov. If you look on youtube for this, you will see all kinds of different centrifugal kits (procharger, vortech, paxton), on different cars, running different bov's.
Centri's use Blow off valves, if you rev the idle passed 4k youll hear the blow off valve working as the RPM's drop, not as loud or shrill as a tubro though. Twin Screw blowers also have "Bypass valves" they just dont make much sound.
__________________
2007 GT Convertible Premium 5 spd || FRPP HotRod Cams || Full Steeda Suspension w D-Specs || Brembo GT500 || Steeda CAI & Delete plates|| Flowmaster || Magnaflow catted X Pipe || MGW Shifter || Tuned by RealSpeed ||
It doesn't make sense at all if you know what a blow off valve does and why turbos use it. A belt driven Centri will not slow down or stall
and there is no lag.
Huh?? It makes perfect sense. Imagine 20 psi slamming into a closed throttle body... bad things will happen without a blow off. A belt driven centri sure has lag, may times its worse than a turbo because peak boost is at peak rpm, while a turbo can hit peak boost by about 3500 rpms.
You could probably glue a whistle in the blow off if you want it to sound like a ricer.
Huh?? It makes perfect sense. Imagine 20 psi slamming into a closed throttle body... bad things will happen without a blow off. A belt driven centri sure has lag, may times its worse than a turbo because peak boost is at peak rpm, while a turbo can hit peak boost by about 3500 rpms.
You could probably glue a whistle in the blow off if you want it to sound like a ricer.
Doesn't procharger ship with a bypass valve? If it does, then it doesn't need a BOV.
__________________
Xcharger with water injection, JBA headers
JBA duals with an H pipe, Roush rear springs, Che K member brace with torque limiters, Cervini's quarter window deletes, Canton polished expansion tank, Roush scoop, Street Scene Elenor grille, custom GT500 chin spoiler, PJ rear louvers, Black rear spoiler, BSM custom stripes, Hurst shifter, Billet interior trim, custom door welts, Autometer dash pod, AEM wideband, Autometer boost & Fuel pressure gauges
I agree it's a terminology issue...
When the throttle plate snaps shut on a supercharger the bypass valve bleeds the pressure off.
A BOV bleeds off boost above a set level. A BOV would not perform the same task as a bypass valve when the throttle snaps shut.
Lag ... another one of those terms...
Lag on a turbo system is the small amout of time it takes for the turbine to start increasing speed when the throttle is snapped open.
On a belt driven system there is no delay in speed... as the rpm increases so does SC speed. Both "lags" mentioned result in a delay pressurizing the intake, but for different reasons. Proper turbine size, gearing/shifting, pulleys along with other mods can reduce "lag" on both systems.
__________________
Xcharger with water injection, JBA headers
JBA duals with an H pipe, Roush rear springs, Che K member brace with torque limiters, Cervini's quarter window deletes, Canton polished expansion tank, Roush scoop, Street Scene Elenor grille, custom GT500 chin spoiler, PJ rear louvers, Black rear spoiler, BSM custom stripes, Hurst shifter, Billet interior trim, custom door welts, Autometer dash pod, AEM wideband, Autometer boost & Fuel pressure gauges
The procharger does come with a bypass valve. That car I saw on youtube was definately not the bypass that comes with the kit. It sounded much more like a blow off valve on a turbo car.
I agree it's a terminology issue...
When the throttle plate snaps shut on a supercharger the bypass valve bleeds the pressure off.
A BOV bleeds off boost above a set level. A BOV would not perform the same task as a bypass valve when the throttle snaps shut.
Lag ... another one of those terms...
Lag on a turbo system is the small amount of time it takes for the turbine to start increasing speed when the throttle is snapped open.
On a belt driven system there is no delay in speed... as the rpm increases so does SC speed. Both "lags" mentioned result in a delay pressurizing the intake, but for different reasons. Proper turbine size, gearing/shifting, pulleys along with other mods can reduce "lag" on both systems.
Where do you get your info?
A BOV is used when the maf is setup in a blow thru setup. A BPV is used when the maf is before the blower intake and the air is already metered. A BPV can generally be used as a BOV valve by removing the recirculating tubing and venting it. A BOV usually cannot be used as a BPV because they typically blow out in a radial way and a tube cannot be easily attached. Other than that they are both vacuum acuated valves to dump boost. A dump valve is what you are talking about and you can set them at different psi to dump excess boost if there is a wastegate issue on a turbo.
No matter how you spin it, a centri will ALWAYS have more lag than a turbo when pulley'd for similar boost levels. Look at some of the boost curves. A turbo will ramp up and level off at peak boost. A centri will increase boost until it starts to choke. So if the turbo and centri are both properly sized, the turbo will DOMINATE the centri at the same boost. I'll define lag as a lack of boost / power.
I made this crappy graph a while back, but it will help. Centris, PD, Turbos, nitrous TQ curves
Procharger blow off valve? 
(Mods in profile)
