Hey guys, on my silverado (6.0L) im running a vortech YSi and everything was running great... making around 13psi (speed density tune). While I was driving I jumped on it and noticed all of a sudden it was down on power making 5-7 psi of boost.

I noticed under a small load, not boost... but around zero inches of vacuum, I heard a weird screech/chirp sound that was intermittent (its only happened when a did a quick jab of the throttle). So long story short, I pulled ALL the belts off (A/C, serp, blower) and it would still do it under a quick jab (while in gear).

So I capped everything off and with my air compressor I supplied around 10 psi of air to the intake tract, and found a coupler that was leaking. But I dont know if that would cause a squeal, as it would still do that with the supercharger belt gone. I fixed it, I didnt hear the squeal anymore... but it was still down on boost/power.

I pressurized the intake again, and noticed my PCV checkvalve was leaking. To me it seems like a minor leak, but how small of a leak does it take to loose a great amount of boost?

I did a compression test, the results were good. So I drove it again, and noticed if I romped on it from a dig, it will just slowly build boost, then around 5K rpms it would just light the tires up. So my boost seems to be lagging, then all of sudden jump up. But then again, sometimes it stays around 5-7psi and doesnt go higher. So it seems to be intermittent. Does that seem like the ball inside of the checkvalve is somtimes sealing and sometimes not?

I did a datalog, everything was good, including timing (no KR, etc). I pulled off my throttle body, elbow, vic jr intake... all gaskets were good and all vacuum lines were good. I pulled the valve covers off, springs were good..pulled the rockers off, pushrods were good.

Im stuck here, i feel like im down at least 100 hp or more. I have a Th400 and on the transbrake it wont even build boost anymore. So it seems like a substantial loss of power, but the only leak that exists is the PCV check valve (its not sealing completely).... and again it seems to me that its pretty minor, but Im not sure how much of a leak it takes to make it run like ****.

Any suggestions or advice is greatly appreciated!

 

Belt slip on the blower?

 

What about a bypass valve, is it not closing properly?

 

That is where I would look too. Wipe the blower down and keep an eye on it, it you see black dust then you have excessive belt dust. Bob