Dump/Blow off valve on 4AGZE how???

[NoHachi]

Quote:An SC does not need a 'blow-off' valve because the supercharger is driven by the crank

Actually, an SC does need a blow-off valve...just like any compressor really. I think the GZE SC already has a anti-surge-valve fitted integrally into the housing.

The need for a surgevalve of BOV is the same between turbo's and SC's. When you suddenly shut the throttle (whether this is before or after the compressor) you get a high pressure area after the compressor and low pressure in front of it. Air tends to flow from high pressures to low pressures and this tendency will start to work against the normal flow direction of the turbo. If this lasts long enough, the end result is something called "compressor surge" which is basically air flowing in the reverse direction through the compressor.

A turbochargers wheel will stall when this happens and needs to be spinned up again when you open the throttle. A bov can improve response time.

A supercharger heats the air every time it passes through it as a result of adiabatic compression. The SC obviously cannot stall because it is always spinning from the crank. What happens is that some air flows back through the compressor, equalises pressures, flows back again into the plenum, flows back into the compressor etc etc. This air gets very hot and can lead to knocking etc. So you use a bypass valve that can equalise pressures whenever there is a vacuum before the compressor. Its a BOV that doesn't dump to atmosphere but back into the intake pre-compressor.

You can do the same thing to a turbocharger BOV, in fact most OEM manufacturers do. This air is already compressed, so dumping it to atmosphere would be a waste. If you dump it before the compressor, it needs to compres the air less and consumes less energy doing so, heats the charge less and responds faster.