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cole930 cole930 is offline
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Join Date: Mar 2000
Location: Auburn,In. U.S.A.
Posts: 2,449

"Cole after reading this several times it seems to me that you have added the bov in the opposite line (turbo to ic) labeled 1 in supplied pic and venting across to the other line (Standard location) turbo supply line or inlet labeled 2 in pic is this correct if so what is the advantage? A shorter track for recharge and does your bov work on vacuum or pressure to the signal line on your bov may it be vacuum or pressure and where do you get that supply."

A blow-off valve (BOV), also referred to as a compressor bypass valve, is a valve which opens and closes depending on the status/position of your throttle plate and turbocharger. It is intended to increase turbocharger life by helping to eliminate compressor surge/back spin and increase performance by allowing the turbo to spin freely between shifts.

To understand how a BOV works, you have to first understand that a turbo's job, described in simple terms, is basically to compress air. It then sends this compressed air to your engine for increased performance. But when you think of what happens during gear changes (when you lift your foot off the gas) and the turbo is spitting out huge amounts of air but your engine is not taking in (hardly) any air the BOV's job becomes apparent. Just like anything that's compressed into a smaller volume than it usually takes up, it wants to expand. So all the air from the turbo keeps pushing toward the (closed) throttle plate and begins to build up pressure there until it finally decompresses and starts to push backwards through your intake tracked back to your turbo where it forces the compressor wheel to come to a very abrupt stop. The turbo experiences what's called compressor surge which, if extreme, can damage your turbo.

Enter the BOV. The BOV is bolted or welded or otherwise connected to the intake tube leading from your turbo to the throttle body. Then a vacuum line is connected from a port on the intake manifold to a port on the BOV.

When the car is accelerating and the throttle plate is open, the pressure in the intake tube and the intake manifold are relatively the same and the BOV remains shut, allowing all of the compressed air to make its way to the engine.

When you lift and the throttle plate closes, the BOV experiences pressurized air where it connects to the intake tube, but vacuum (because the throttle plate is shut) from the intake manifold. This difference in pressure opens the BOV and allows the compressed air to exit from the intake tube via the BOV outlet. The compressed air can be discharged to atmosphere or recirculated, through tubing, back to the intake tubing before the turbo inlet. Since none of the air reaches back to the turbo two benefits are realized by keeping the turbo spinning:

1) Compressor surge does not occur, increasing the longevity of the turbo.

2) Since the turbo never stops, you spend less time getting it up to speed again when you reach your next gear and begin accelerating again.

It does not matter where you mount the BOV, it's how you plumb the Bov mounting port and recirculate port. You can put the BOV in the trunk if you want as long as you tie the BOV piston side (after the turbo outlet and before the TB) and tie the recirculation side (after the fuel distributor and before the turbo inlet)

Look at this one:

Hopes this helps clear things up for you.

Cole - 80 930 "The Old Sled"
Mods: TurboKraft Custom IC, 934 Headers, GSX 61, Zork, Port Work, SC Cams, Air Mod Fuel Dist Relocated, Water Meth Injection, BL WUR, MSD 6530, Greddy EBC, Synapse Bov, Short 2nd & 3rd with 8:37 R&P, Wevo Shifter, Coupling, and Mounts, MTX-L SSI-4, Big Brakes, Rebel Coilovers, Bilstein Sports.

Last edited by cole930; 12-16-2010 at 11:36 AM..
Old 12-16-2010, 08:33 AM
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