Holy crap that was a fast reply.
I was going back to edit my post to add that they may use the bypass valve for compressor surge, but the main benefit seems to be the economy, at least from Magnuson's marketing.
I'm still not convinced (or maybe I should say I don't quite understand) that the Roots bypass valve does anything for compressor surge though. On the 4th gen Magnuson blower, the bypass is an air path from directly before the compressor vanes to directly after. The throttle body is located well before the compressor. My understanding is that compressor surge happens when a downstream TB slams shut and the compressor continues piling air up behind the TB. If the TB is located before the compressor, there is no wall to slam the air into.
Now, whether the bypass is open or closed, the vanes are still going to be starved for air by the closed throttle body. Since any air that does not get sucked through the bypass and gets compressed by the blower has a relatively straight shot into the cylinders, there is no wall to create compressor surge. How does the bypass limit surge if there is nothing to cause the surge?
I'm not trying to be a dick by disagreeing with you, I'm just trying to show you my thinking so that you know how to approach an explanation that will make me understand. You seem to have a lot of experience with magnuson blowers, so please fill me in.
Hopefully this will make sense in the morning.
Oh wait, I think I might have it. I may be looking at the airflow through the bypass backwards. I assumed that when the bypass was open, the air went right through there into the engine and completely avoided the compressors. What you're saying is that the bypass valve allows air that comes out of the compressor to be rerouted directly in front of the compressor again, so that it is not starved of air, and thus prevents cavitation (assuming that is what causes the cavitation. And exactly what do you mean by cavitation, since the only meaning I'm familiar with has to do with bubble formation in a liquid from rotating parts)? The way it was explained on Magnuson's and whipple's websites makes it sound like all the air goes through the bypass, and none through the compressor. Was that written by the marketers to try to dispel the myth of superchargers causing huge amounts of parasitic drag in normal cruising?
Hopefully nothing in here sounds confrontational, I'm just trying to get this figured out. And get my posts up to 100. I think this thread might do it.
Bob
Edit: If roots bypass valves aren't there to help with fuel economy, please ask Magnuson to fix his website next time you talk to him, since his site clearly states otherwise.
