BOV, blow off valve?

[latamud]

Hello,

I am planning on running about 12# boost supercharged on a Ford 351W. My vortech B-trim comes with a cheap plastic bosch bypass valve. Do those things really hold up? I was thinking of getting a BOV but not too sure about them. Can I use a turbo BOV for the supercharger? Do they react to the pressure only or is there a CFM rating for each type? I was looking on ebay and see the adjustable ones ranging from 8-20 psi. I figure they are similar to a fuel pressure regulator with a return bypass. I spoke with a turbo guy last night and he didn't really answer my question. He said an american car needs an american BOV so check with edelbrock. I didn't know edelbrock made BOVs. Thanks for any input.

[ray95]

You can't use a stock BOV in a vortech supercharged application the way you are thinking. Here's the reason why:
A bypass valve is recycling the unnecessary air back into your supercharger inlet tube to be reused. This is important because your Mass Air Meter has measured how much air is supposed to be going into your motor. The computer expects this and adjusts accordingly. Now if you use a BOV, the excess air is being sent to the atmosphere instead of back into the blower. Now the computer thinks air is there that really isn't and you run into all sorts of idle/surging problems.

I've seen a BOV used before but I can't find the link. It was modified to send the excess air back into the system to be reused. The phssshhh wasn't that loud but it still sounded cool. You can get racing bypass valve instead of using the stock valve.

Hope this helps.

[latamud]

What about carburetor application? Sorry I wasn't specific. I notice on down shifting or hard sudden braking when I have to let off the accelorator that I have too much air coming in but not enough fuel, especially at the end or the 1/4 whe nI have to slow down. I end up choking the engine out. I figured letting the excess air exit through a BOV would fix it.

[ray95]

when you decelerate or let off the gas the excess air needs some where to go when the butterfly is closed so it won't force its way back to the supercharger or turbo. a bov or bypass would relieve this compressor surge on deceleration. the problem you are describing sounds like you have TOO much gas and not enough air....hence choking the motor.

what exactly is your setup? do you have it listed some where? you can try a bov, in a carbed setup it might work but this will be to relieve compressor surge. as long as you don't need to meter the air anywhere (which you shouldn't). as far as needing an "american" bov, i think that guy was full of it.

[latamud]

I have a 351W with 650 double pumper, manual tranny. Paxton SN-93 supercharger 6lbs. At the end of the 1/4 when I let off the gas, and step on the clutch the engine hits some high rpms while I coast but my foot is off the gas so the butterflies are almost closed. The high rpms also affect the supercharger pushing loads of air through the closed carb. After this happen I notice a rise in the coolant temp, I assume because of running lean at that moment. Now with 6lbs of boost I'm not reunning a bypass nor BOV. I am guessing the air that can't go through the carb ends up pushing back through the charger. I also figure, if I plan on 12# on a Vortech with bypass it will be worse. The Vortech has the cheap plastic bosch bypass. I am thinking of using a universal BOV in its stead and plugging the hole on the charger intake side that the bypass was running to. Thanks for the ideas. Still new to this and trying to figure it out.