a quote over from good old Turbomustangs.com by TurboShortBus
"Keep in mind that the ECU shuts down the injectors when engine RPM is greater than 1700-ish and the throttle goes closed. The "momentary rich" condition with the BOV after the MAF that everybody talks about isn't there.
He was refering to a turboed car, on a blown car with a draw through maf setup is screws with the readings because with the bypass the air is recirculated back into the blower inlet pipe and put through the motor again. If there was a BOV to the atmosphere then that air would be gone but the computer would think it is still in the engine and screw up the tune of the car. I dont know what the effects would be but Im sure it would be to great.
If you had a blow through maf then you could run a BOV just in front of the maf without any issues.