Blow off valve not opening

volvee850glt · Post by **volvee850glt** » 04 Mar 2010, 18:46

I knew it was only supposed to open after the throttle was closed. I did not know it has to be near redline though.

Post by **vegasjetskier** » 04 Mar 2010, 18:57

volvee850glt wrote:I knew it was only supposed to open after the throttle was closed. I did not know it has to be near redline though.

OK, "near redline" might have been a bit of an exaggeration. But testing it at idle sitting in your driveway is not going to cut it. You at least need to rev the engine up somewhat so that a high vacuum is created when you let the throttle slam closed. My Mitsubishi was very reluctant to do it this way, but I could confirm it was working. It did work well when I was actually driving the car, though.

Can you post some pics of your setup so we can try to figure out what's going wrong?

volvee850glt · Post by **volvee850glt** » 04 Mar 2010, 19:11

I will try to post some pics tomorrow. I have been taking down the road so it has a chance to boost up some though.

volvee850glt · Post by **volvee850glt** » 05 Mar 2010, 21:53

I never got a chance to take any pictures but I found some on a forum for rx 7s with the same problem. I know that it should be closed at idle but on the rx 7 site it says it should be open at idle because it is under vacuum. That kind of makes sense because my boost gauge reads most vacuum at idle. But it doesn't let the engine idle smooth then after a minute it dies. Is there something different with the rx 7 engine or do they just not know what they are talking about??

Post by **JDS60R** » 06 Mar 2010, 10:33

Do you have the BOV before or after the throttle plate? (as the air flows - compressor is before -intake is after)

A blow off valve is placed between the turbo and the throttle body. If you have it on the intake manifold (after the throttle body) it won't work. After the throttle body the wastegate regulates the pressure and is opened as soon as you let off the throttle. The BOV is after the turbo compresser(intake side) to handle the overpressure when the throttle plate is closed and the pressure is forced back against the compresssor wheel. A BOV is in place to keep the turbo from damaging the compressor.

I am not saying a poorly sized wastegate experiencing boost creep could not use a BOV in the intake but for a normally set up turbo you won't see any action at an intake mounted BOV.

Post by **vegasjetskier** » 06 Mar 2010, 12:24

volvee850glt wrote:I never got a chance to take any pictures but I found some on a forum for rx 7s with the same problem. I know that it should be closed at idle but on the rx 7 site it says it should be open at idle because it is under vacuum. That kind of makes sense because my boost gauge reads most vacuum at idle. But it doesn't let the engine idle smooth then after a minute it dies. Is there something different with the rx 7 engine or do they just not know what they are talking about??

I can't imagine why you would want it open at idle. It would be admitting unfiltered and unmeasured air to your engine, causing it to run poorly and wear out faster than normal.

volvee850glt · Post by **volvee850glt** » 06 Mar 2010, 14:17

No it is before the throttle body. And yeah it didn't really make much sense to me i was just wondering.

Blow off valve not opening

Re: Blow off valve not opening