Blow off valve issues...

[paxton350]

ok i welded a BOV onto My S/C intake arm however i think im still getting unmetered air into the intake manifold since the motor just dies at idle almost randomly... theres also some sputtering from a dead stop once in a while... im not sure if this is faulty BOV or not... when i bring the idle up to about 2k rpm i can feel air coming out of the BOV... ( i mean if the throttle is open the manifold should be sucking in ALL air correct? it doesnt matter how open or not it is right?) i think it (BOV) is leaking boost and the mass air sensor isnt picking it up... the only thing i can think of is if i ran a hose from the BOV to before the mass airflow sensor... im running 9# of boost this season and want to maintain the longevity of the blower since i just rebuilt it but this BOV is really a pain! a few months ago i just put a piece of tinfoil and completly bypassed the BOV and the car ran mint but i want to take advantage of this thing since its on there any suggestions?

-chris

[raroZ28]

I don't smoke, but a buddy of mine does, and when I thought i had a leak, i couldn't feel with my hand, he put his cig in front of the bov, and sure enough it sucked the smoke in.

I had a TurboXS H-RFL and it came with washers. Pulled the BOV apart and put in a washer and it fixed the problem.

[Kevin - Blown 95 TA]

Chris, what pistons do you have in there?

And do you still have a bypass valve? At 9# all you need is the bypass routed to after the MAF.

[paxton350]

interesting im going to see if i can pull it apart tommorow raro... where did it need washers and why? Kevin it still has the stock top and bottom end minus 1.6 rockers... it only has 95k on it so its still a fairly young motor. the particular paxton kit i have didnt come with any type of bypass valve, i would have to weld on before the maf...

[raroZ28]

The end of the blowoff valve where the nipple comes off for the hose that runs to a TB port... You twist that end, and there is a spring in there and that's what keeps the BOV closed. If the BOV doesn't close all the way, you'll have a leak, so you take it apart, and put the washer in. It makes a tighter seal and should close the BOV up if it's staying open a little bit.

Like I said my kit came with washers, I'm suprised yours didn't. What kinda BOV do you have?

[Flash 97 WS/6]

A blow-off valve should not leak ANY air in or out except durring excessive boost. In your case probably >15 psi. (if this sounds stupid, please take a look at my next post) You should have positive intake presure before the throttle body at the 2k you mentioned because the throttle blades are barely open...the intake (engine side of the throttle body) will not go to a positive pressure and be able to use all of the blowers extra air until the blades are nearly full open because the engine is still trying to vacuum pump way more air out of the intake than can get by the small opening even with some positive pressure on the outside. On my setup, I get well over 20# of boost on the outside of my throttle body when revving high but not really "opening it up" when not using my bypass valve.

It sounds like your BOV is either not adjusted for a good "Full Closed" position or the actuator (in a BOV, probably just a spring?) is allowing it to open it at way to low a pressure.

Just FYI, I plumbed and re-plumbed many times before deciding on locating my MAF back to nearly the stock location. When it's the last thing before the intake, you can bleed-off air from the business end of the blower any way you want and not worry about it not being metered accurately. I never could get things to feel right with the MAF on the intake side of my blower where ATI, Powerdyne and I believe most others normally locate it.

[Flash 97 WS/6]

Also, if you have a vacuum hose that runs to a port on the intake from the valve in question, then you have what I call a Bypass Valve rather than a blow-off valve. In that case, is should be allowing quite a bit of air to freely flo through unless the intake vacuum is at 0 or greater. The trick is that if it's after your MAF, you have to route that air back into the intake somewhere AFTER the MAF but before the blower to create a closed loop (or cheat and move the MAF after the bypass valve like I did )...if you run it back to before the MAF you will actually increase the amount of air the MAF sees passing it that never gets mixed with fuel in the engine...making the inaccuracy even worse.