to my knowledge they both prevent compressor surge into the turbo, thus providing the turbo with better spool up times and durability. now my question is, what is the only potential difference between the two? i know the 13bt comes standard with a bypass valve but some say its too small and just to get a larger one or a blowoff for applications moderately above the stock limit, say 230-250 hp.
will the bypass also make the signiture blowoff sound or will it stay quiet like the stock bp valve?

 

btw, would the larger bypass valve replace the stock one or do i have to fabricate some sort of elaborate contraption for this to work?

 

The only difference between the two is that the bypass valve recirculates the air, while the blowoff valve discharges the air from the system.

An engine with an airflow meter is supposed to have a bypass valve. This is because the air has already been metered by the airflow meter, and the amount of fuel to be injected has already been determined by the ECU. If the metered air is discharged from the system by a blowoff valve, the ECU has no way of knowing it, and it still injects the same amount of fuel that it thinks it needs. Since there is less air than the ECU thought, it creates a rich condition, which causes hesitation and/or stumbles. Unlike a blowoff valve, a bypass valve retains the air in the system, and the correct air-fuel mixture is maintained.

If your car has an EMS which runs in speed-density mode (with a MAP sensor instead of an airflow sensor), then it doesn't make any difference if air is discharged because the MAP sensor will still sense the correct air pressure.

Many people install a blowoff valve on their car because they like the noise it makes, even if the airflow meter hurts the acceleration times a bit. A bypass valve will stay quiet.

The stock bypass valve works just fine. You will notice a distinct fluttering compressor surge noise upon rapidly closing the throttle after boost if your engine is running too much boost for the stock bypass valve. If the bypass valve is not up to the boost level, it will still bypass what it can, so it's not like it will have a total failure. A few minor compressor surge occurrences are not going to hurt the turbocharger's center cartridge, but it would be a good idea to consider installing a larger valve if this happens.

BTW, if you experience compressor surge on acceleration, this is because the turbocharger is making boost too fast. This situation has nothing to do with a blowoff or bypass valve, but rather needs to be fixed by adjusting the wastegate or by changing out turbocharger components.

 

Most people who get to that point have a custom intake system, anyway. All that is needed is an extra pipe that goes from the bypass valve to a point between the airflow meter and the compressor inlet. I wouldn't exactly call that elaborate.

 

haha thanks, bypass valve it is then.

 

Hmm...quiet, so they won't KNOW you're running boost...well the turbo has a nice noise but still, it's a little more subtle.

 

You can always remove the pipe and make the bypass valve into a BOV if you like, but it is pretty difficult, and sometimes impossible, to make a BOV into a bypass valve. If you start with a bypass valve, you can try running it as a BOV to decide if the cool noise is worth the slight rich condition.

Honestly, your best performance is going to come from throwing the AFM in the trash where it belongs, and converting to a standaone EMS (which almost always uses a speed-density system). However, I understand that this is more complicated and expensive than most people would like, and is not the solution for everybody.

 

BOV for life :P