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

[Lauren]

NoHachi Wrote: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.

No it doesn't not on the 4AGZE. The only reason that the GZE has an ABV is for releasing excess boost when it actuates at 0.8 bar.

When you fit a big pulley you remove or blank off the ABV. No ill effects result of this. You have to do this to release the increased boost of the big pulley.

Pressure isn't an issue on the SC because the SC is not before the throttle body. In fact a GZE is more responsive when the ABV is taken out of the equation. From your reasoning you would need a BOV on an NA.

Don't forget the SC is on a clutch so it is not engaged all the time. Airflow will spin it slowly.

I fully understand the reasoning for a BOV on a turbo setup, but it is not the same on the SC setup on the GZE.