I think in understand why to use one on turbo-charged cars, to prevent the initial surge from lifting the gas from damaging the impellers(sp?), but the few pics of superchargers I have seen showed very solid looking screws for compressing air. Didn't look like they would be damaged by a surge. So is there a reason other that the sound to have one?

 

Its for the same reason as when turboarged.

You can't tell anything by how beefy the parts "look."

Plus, the main reason for turbo cars is throttle response. without the BOV, the pressure going back against the compressor will slow it down, even stop it. Then, when you get back on the gas, you have more lag waiting for it to spool back up. With the BOV, the turbo doesnt slow down as much between shifts.

But, for an SC, its for durability reasons.

 

The Stillen/Vortech SC is a roots blower, it is pulley driven but the supercharger core is very similar to a turbocharger. It still has a small delay to spool up and deliver the air back into the intake manifold. Thus, when you shift there is still an excess charged headed to the manifold, the BOV releases it just like a turbo.

 

FYI, The Stillen/Vortech SC is a centrifugal blower. Roots blowers are the eaton/magnussen types. (i.e. Jackson racing)

 

it sounds nice

 

If you don't release that back pressure it tries to spool the turbo backwards...