1G blowoff valve ?'s

[Red350DropTop]

Guys,
I am thinking about using a 1G blowoff valve on my custom supercharger setup for my non-mitsubishi car. I searched the forum and did not find an answer to a few of my questions...

I am putting about 6psi into a 355 inch motor. Less boost but more CFM than what these valves are designed for.

Why are people "crushing" the 1G valves? Are they physically crushing the housing for the vacuum diaphragm? What exactly does this do to the blow off capabilites? Does it just increase the valve's boost handling capabilities or does it also change the inches of vacuum required for blow off?

Does anyone know what inches of vacuum the uncrushed 1G valves blow off at?

What about the inches of vacuum for the 2G valves? I know they are plastic, but I am not running the boost you guys are.

Finally, what are the outlet sizes on the 1G and 2G valves? Would one be better for me?

P.S. I have been really impressed with some of the numbers you guys are putting out with your motors. Who knew?

[FourG63 97GST]

well the 1G bov leaks at about 17psi, crushing it put more pressure on the spring, therefore it holds more boost

too tired to answer the rest right now
nite folks

[kjewer1]

Yes we crush the vac canister part, or the actuator. As he said above, to put more pressure on the spring. This requires more boost on the underside of the valve to blow it open, but it also increases the vacuum required to open it. But in typical operation, its vauum PLUS boost that opens it. Just for reference, ideally a 1g BOV will be crushed until it takes 18" to just crack the valve off its seat. 19" is acceptable too, but getting close to the limit. At 20" and up the valve gets pretty noisy as it "flutters."

Even an uncrushed BOV will work fine for the boost you run, and stock they start to open somewhere around 12" if I remember correctly. But as you suggested, I would be more worried about flow. At least on a turbo system, I'm not sure how critical it is to evacuate all of the pressure in the piping for a supercharged application. But for the amount of air mass/volume you need to get 6 psi, it may be a bit small. Something larger like the Tial BOV might work better, though its pretty damn stiff. But hey, 1g BOVs are only 40 bucks used, might as well try it. Are you plannig on using it as a bypass valve also? (to divert the air from the blower to atmosphere while just cruising along)