Thread: New type of BOV
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BoxxerSix BoxxerSix is offline
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Join Date: Jun 2006
Location: Ballston Spa, NY
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Originally Posted by beepbeep View Post
Hmm...I believe you have oscillation/coupling problem made possible by 1. Quick spooling turbo 2. More boost 3. Valve that opens too easy. 4. Probably some MAP enrichment when mass flow starts to increase. 5. Weird compressor map

I suggest trying this:

1. Find a adjustable recirculating BOV, make sure it dumps air back between turbo and MAF, but as far away from MAF as possible. Don't us pop-of function.

2. Adjust it little harder, so it doesn't start opening and dumping until 4lbs

3. (If above doesn't help) fit a small strangling/delaying orifice between BOV articulation nipple and the hose to get rid of transient surging.
Goran thanks for the input. All of this was actually tried months ago in many different formats with many different types of valve to no good effect. It only resulted in poor DV response and high amounts of compressor surge at throttle liftoff(shifting) as the valves reacted way to slow.

Issue turned out to be the compressor running over the surge limit when the engine wasn't calling for air. Just a bad case of a small, really fast spooling turbo at high PR's that just has a very narrow map.

I was going post last night but the bleed setup has solved the problem and the dyno runs yesterday proved no issue with it. Everything has been tuned properly and the car runs great. I didn't want to post this yet as I haven't digitized the dyno sheets to show the TQ/HP curves and their changes as well as the AFR plot and wanted to post those with the end result to sho the differences.. Plotted standard setup pull against my bleed setup. Had to sacrifice a tiny amount of power right from the start as the previous tuner of this car had it running on a bit of a knifes edge. 9 counts of knock and bit if a lean AFR at peak torque forced me to make the tune more conservative by adding a bit more fuel at peak torque and pulling timing in a few places. I barely had to adjust the AFR up top during the bleed, it was pretty much right on target where we like to tune these cars anyway. End result is a car that runs superb and is completely drivable right now. Down ~15 hp/10tq, but not because of the valve and bleed setup. Customer is more than happy with that as 300 driveable HP is better than 315 that you cannot use at all. He even stated he's not capable of driving the car for all it's worth so 15hp isn't going to affect much for him.

Adam Hennessy
Old 01-31-2008, 05:01 AM
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