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While I had the air tube between the Turbo outlet and the engine removed, I noticed this valve attacted to the tube with a directional arrow on it. One one end it connects to the air tube coming from the air cleaner. The other end goes into the tube leading to the engine intake which the valve is attached to. I don't know just what this valve does, but with the driveability problems I have been experiencing, I wondered how to tell if it is installed the right direction. The arrow points toward the air cleaner tube, where it connects to the box behind the MAF.

It is the 'BOV' ... the arrow should point toward the air cleaner / in front of the turbo


Like that :

I didn't know we had a blow off valve. Whats the difference between a blow off valve and the wastegate in the turbo?

Mike

Their purposes are actually unrelated.

The wastegate is a valve that lets exhaust gas go around the turbine instead of through it. When it opens, the turbo stops building boost because nothing drives the turbine. It is controlled by manifold pressure and basically it opens when pressure reaches a certain level. It reaches an equilibrium at maximum boost.

The blowoff valve is a valve that lets air coming out of the compressor back into the compressor instead of into the engine. It is also controlled by manifold pressure except that it opens when manifold pressure is below a certain amount. The idea is that whenever the throttle is closed, manifold pressure will be low, so the blowoff valve allows the pressurized air from the compressor to keep moving rather than slamming into the shut throttle body. This reduces the stress on the turbo and also allows it to maintain a little boost between shifts.

in fact, it's called a "Air bypass valve" since it returns the gaz in the intake...


In big, the Wastegate controls the spinning speed of the turbo, so the pressure in PSI (the faster the turbo spins, the bigger the PSI are), by letting exaust gas pass through the turbine of the turbo, or by a 'derivating' tunel.

For the BOV : when you are WOT, the flow of air between the Turbo outlet and the Throttle boddy is pretty quick, and the turbo has to push a lot of air to build pressure despite that quick flow of air. So when you suddenly release the gas pedal (for shifting.. or else ), then you quickly close the throttle body, but the turbo still spins pretty quick and push a lot of air. This could build a lot of pressure, and it even creates a "wavefront" that bounces from the throttle body plate towards the turbo.. and could damage the turbo. To avoid that, when you release the gas pedal, the BOV (or bipass valve) opens and let the pressure and the flow of air escape.

Hope this is clear for ya, if not, ask somebody else that is more "at ease" with english

ahhh, great I get it. Thanks

Mike

Thanks, great explanation. I see the arrow points on direction of airflow, quite logical, now that I know what the valve does. Great picture, too. I never knew these cars had such an avid following. This is the first foreign car I have purchased. I bought this car when I had to sell my GTP, due to having 2 mortgages. I was looking for the "best available athlete", as Chuck Noll used to say when the Steelers were getting ready for the draft, back when they actualy won Super Bowls. The owner still had the original sticker, ($21,925) and most records. At that time, with 84,000 miles on teh clock, it had never had other than normal maintenace. After 9 years on the road and 123,000 miles in Pennsylvania, it still has the original exhaust, which amazes me. The clutch went 110,000 miles, not bad for around here.