this is from the slk32 --170 engine on MB world

The bypass valve on a supercharged motor puts the extra air from the SC back into the airbox when the engine is under low load. This is so that you get good fuel economy, but when you need it, the bypass valve closes so that the air is actually forced into the motor. Its not the same as a BOV on a turbo motor. I dont see any advantage to going to a aftermarket valve. It wont even make a sound, well maybe like a leaking airhose! Although I may be wrong, some one feel free to correct me.
sorry, I'm not so sure about your reply.

I'm still a noob for superchargers, however, I'm a pretty well informed turbo motor user.

The bpv won't open or close solely based on the load of the engine. Stock BPV will hold the compressed air between the supercharger and throttle body. If there's excessive compressed air between supercharger and throttle body, say at 14 psi, you decided to let off the throttle, the bpv will recirculate the unused air between the supercharger and throttle back to the intake tract. The stock bpv won't make any sound because of the recirculation, however, if you install an aftermarket blow off, it will.

On the M271, i see that it's possible with a custom flange and bov base. Some aluminum welding and a plug for the stock recirculate hose will do it. The only draw back is the drive by cable on the MB, on the Subaru, it's possible with either drive by wire or cable.

Also, if you want blow off sound, changing the rubber recirculate hose to a metal pipe will produce that sound. However, the supercharger muffler will kill most of that blow off sound.

All in all, i'm just seeking for the blow off sound, i know fully about the pro's and con's of a bov vs. bpv. i.e. lean/rich , cel codes, rice/not rice, ...etc.

here is more --------------Superchargers have larger and heavier internals than turbochargers

If, when you hit the gas about midway (mid throttle but no boost yet, yet high demand) that inrush of air that you are demanding will not reach the engine instantly because it has to go through the supercharger.

This delay will cause a lag much like turbo lag on throttle input, further, it will decrease fuel effeciency for 2 reasons

1- all the air you're injesting in around town driving would be hot having run through the supercharger
2- you will waist some 10-15 hp of 'milage' always driving the supercharger (and as you know it's not a light thing to drive like a ceramic turbo compressor wheel).

To solve this, supercharges use BYPASS VALVE S (not blow off valves)

a blow off valve vents air on throttle lift to prevent compressor surge.

a bypass valve has 2 functions
1- it vents air on throttle lift to prevent compressor surge
2- it completely BYPASSES the compressor (be it a turbo or a supercharger) on high vacuum / high demand situations to promote throttle response and high effeciency (milage) under off boost driving conditions.

If you took out your stock electronic bypass valve and installed a blow off valve your drivability will suck, your thorttle response will be ****, and your milage will drop significantly as you will technically ALWAYS BE using your supercharger...and very quick into boost (which can hurt traction too)....

the old style bypass valves (like the ones that come on stock mr2 turbos, stock 911 turbos, stock saabs..etc) are vacuum referenced

at high vacuum it will bypass ... this high vacuum is present in 2 situations
1- throttle lift (so it will work as a blow off)
2- high pressure differencial between manifold vacuum and inlet vacuum (ie high demand/high restriction situations where the S/C is 'lagging' or choking the airflow

Newer cars are more fancy using an electronic bypass valve.
With this bypass valve mercedes can do 2 things

1- simulate a mechanical (vacuum referenced) bypass valve
2- limit boost in situations where it wants to (such as traction control for example... the ecu is able to reduce torque output by reducing throttle angle, and opening the bypass valve dropping you out of boost...and then with the aid of selective braking, the ecu is able to re-stabilize the car using ESP)

another nifty feature to this electronic bypass valve is that mercedes if they want to can use it kind of like a wastegate...where they can open it to limit your boost, or limit your 'spool' (how fast the boost builds) even on a roots type supercharger.