[Blown353]

Kris, depends on the CFM being moved, boost level, and volume that needs to be "dumped" when you close the throttle. The smaller valves can't move as much volume as quickly as a larger valve and you might get compressor surge. Also the poppet-type valves tend to react faster than the butterfly style valves.

Rev the car really high and snap the throttle shut... or take it up to redline in a gear then leave it in gear and just take your foot off the throttle. If you don't get a chattering sound (usually sounds like "cha-cha-cha-cha-cha") then you aren't getting compressor surge and don't need a bigger (or faster acting) bypass.

The smaller black plastic Bosch bypass valves work well for lower volume / lower boost applications. A single Pro-Flo valve seems to work well up until around the 700-750hp level (around 1250 cfm or so) and then you either need to run two of them or step up to a larger poppet style valve.

The poppet style valves (i.e. red Procharger "Race", Vortech Mondo) are fast responding and move a large volume of air... that's good. Unfortunately they are also really loud. On the air/water car I did it used an F1R headunit and a Procharger open-style Race valve... in the car all you really hear is the damn air coming out of the bypass valve. It's really loud and very obnoxious. Probably would have been better off using the hose-connection style Race bypass and running it to a large breather or something similar to help muffle the noise.

I run two of the Procharger "Pro-Flo" valves on my car. I used to run one and it worked fine with my older P1SCH and non-intercooled. Once I changed to a D1SC I started getting very light compressor surge above 5300rpm or so. Then once I added the intercooler it got real bad... the single valve just couldn't dump all the pressurized air fast enough during shifts and when I'd let off at high-RPM it started to get pretty severe compressor surge. The intercooler & added piping meant a much larger volume of air needed to be dumped at every throttle closing so the system needed a larger "vent" to prevent compressor surge. So I added a 2nd Pro Flo bypass. It was cheaper than buying a Procharger Race bypass (or a Vortech Mondo) and 2 of the Pro-Flo's are fairly quiet. A Procharger "Race" bypass is LOUD. No more surge issues.