Thread: New type of BOV
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Join Date: Jun 2001
Location: Sweden
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Originally Posted by BoxxerSix View Post
Goran, I'll answer each separately for you

This is correct for the most part. This particular car has a host of aftermarket parts, including aftermarket 272 degree camshafts. Other cars that suffer from this problem though range from nearly bone stock to fairly modified.

That was a mistype on my part in my previous post. Turbocharger boost is set at 25psi, controlled by it's own boost controller(off the compressor housing for boost only signal). Valve is set at 24psi, also with it's own boost controller(also off the compressor housing for a boost-only signal)

Car is a hot wire MAS setup. OEM location of MAS is bolted directly off airbox, rubber corrugated tubing connects MAS to turbo inlet ~ 16" total length. This car is equipped with aftermarket style tube intake, other cars of different makes of intake as well as the stock ones. Filters. wheather OEM or aftermarket, are in very close proximity to the MAS if not bolted to it directly.

Car throttle is standard cable actuated(non TBW). Diverter valve is a recirculating type in OEM setup and is still recirculating with the new Synapse valve on the car. The recirculation dump on the intake tube has been moved and adjusted several times to see it's effect on MAS signal(no disruptions). The dump resides between the MAS and turbo inlet, OEM has it about 6" from the MAS

Yea it's not the standard Td04 map I believe. Compressor was changed a bit and it's specific to the Evo. I have it here somewhere, I'll look for the file. I don't have it labeled as "evo16" or something like of that nature like a smart person would OH!:

On the stock BOV setup, the car operated as normal except this venting issue. The valve is shut anytime you are over 0hg plenum vacuum and doesn't vent at low engine loads/speeds UNLESS you start doing this throttle modulation. At low rpms(1500rpm and under) it's not that apparent as you're barely moving. However once you start to climb 2K rpms the situation get worse. The real big issue is when it's occurring at 4K+ rpms with some speed behind you. Any attempt to modulate the throttle at these engine speeds will surely have the valve open and dump back to the intake under load, releasing all boost pressure that the engine may be calling for.
The turbo on these cars is one mighty fast OEM spooling turbo. In most cases your capable of building 6-7psi of boost at a standstill by simply giving the motor a quick rev up to 5-6krpms. BTW, if it mattered OEM rpm limit is ~7200 but in most cases with valvetrain mods we swing these motors out in excess of 8500rpm all day long.

With the new valve it does exactly as you said there. It's closed all the time except when it needs to bleed off an extra 1-1.5psi of boost pressure at WOT and/or in between shifts to vent airflow and prevent compressor surge like any other valve does. I have easily compensated for this ~1psi of air bleed through the stock computer and AFR's are right on track throughout the RPM and load range of the motor. With this setup, I am able to completely modulate the throttle from 6hg to any boost level with zero dumping/bucking issue now(6hg vacuum mark is the limit to open valve for shift set by adjustable vacuum switch)

Also, the bleed air from the diverter valve is recirculated back into the intake post MAS/pre turbo as it is OEM.

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.
Thank you for your time,
Old 01-31-2008, 02:48 AM
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