Bob,
If you re-read my post above you'll see that both the blow-off valve and the bypass valve perform the same function, without being the same thing.
Blow-off valve vents the compressed air stack to atmosphere (out of the car's intake system). Good only on MAP sensored engines. Loud pschht sound.
Bypass valve is plumbed back into the system downstream of the MAF. That way air that has been metered is not lost. Imperative to use that on a MAF sensored engine. Mild pschht sound.
See? Demon is right, they are not the same item, but I have to add that they do perform the exact same function.
