Also, there is a difference in "compressor surging" and just not being able to properly evacuate compressed air from the charge pipes... Compressor surging is when the compressed air in the charge pipes wants to flow back through the compressor housing, resulting in air flowing back out of the air filter, effectively reversing the compressor direction temporarily.

This can only happen in high-load to no-load transfers on turbo cars (there is usually not enough boost to cause surging at low-mid load situations). If you go from high RPM (high boost situation on a SC) to low RPM (low boost situation on a SC), but still have load on the throttle (if it is at an RPM higher than idle, there is load), the throttle body is still open, so compressor surge cannot physically happen (compressed air goes into the intake manifold via the open throttle body). If you go from high RPM (high boost with a SC) to no-load (i.e. - idle with a SC), then it MIGHT happen, but the SC compressor is still tied to the crank, and spinning forward. I do not see how it could even possibly come to a complete stop, and then spin backwards, like what happens in true "compressor surge" situations (that noise you hear on surging turbos is the turbine cartridge slamming to a stop (or at least slowing down ridiculously fast compared to normal situations), and even rotating backwards a bit, from a few thousand RPMs in the fraction of a second).

I hope all this made sense!

John

 

So you're going to tell me you 100% believe this statement of yours:

"With a SC, the instant you let off the throttle, and the throttle plate closes, the SC stops boosting immediately (as it is tied directly to the crank, which drops to idle (no boost) when the throttle plate closes)."

You think an engine drops to idle every time the throttle plate closes? I tell you, when I'm done with a run through 4th and 5th gear and finally let off the gas I certainly don't put the clutch in and allow the engine to drop to idle at 100+mph. If I'm engine braking at 8000rpm you better believe the SC is spinning like crazy and trying to pump boost into the engine (but isn't because the BOV is venting).

 

Compressor surge happens the same way in both cases. Turbo or S/C doesn't matter. In either case you have an air pump spinning when you let off the throttle, and surge will happen on any centrifugal air pump when your pump is spinning and airflow through that pump comes to a stop.

Which one slows down faster is irrelevant, because neither of them is able to slam on the brakes and come to a halt the second you decide to let off the throttle.

 

Correct, everything else said in this thread that claims the opposite is just guess-talk from someone with terribad physics knowledge.

 

It's the BOV. You can't use the HKS SSQV. The local shop told me they tried with s/c setups and it's no go. I know it's the shit for turbos and we love it but for s/c's, it just doesn't open properly. You need something really loose like a Greddy Type-R or Type-S, etc. Do a search for others that also work. It sounds exactly like your issue as the s/c bov will stay open at idle (you make like ~1psi of boost at idle). The HKS just springs closed.