I've posted this in "Advanced Tech", but he more info I gather, the more this looks like a Forced Induction problem rather than a blowby problem.

The engine is a forged 383 LT1 with a home-build PT-76 GTS turbo. The crankcase vent hose is attached to the inlet of the compressor.

I ran it for a while at 12 - 14 psi with no real issue, but it dyno'd low (520 rwhp versus 540 rwhp with the old supercharged setup). I traced the problem to a restrictive IC - TB pipe, so I built a new larger one and removed the BOV.

With no other changes, the turbo now produced 18 psi. I ran it like that for a while even though I heard hints of detonation now and then.

When I removed some intake piping to change a gasket, I found alot of oil in the IC - TB pipe. As a diagnostic step, I ran the crankcase vent hose into a plastic bottle.

Last Friday night, I brought it to the track and was underwhelmed by the performance. I ran some 11.0's at 125 mph at 15 psi, and then raised the boost to 18 psi for a 10.7 at 134 mph. This is disappointing because it ran 10.40 at 132 at 13 psi with the supercharger.

During the 3 runs, it accrued about 1 cup of oil in the bottle, which sounds excessive to me, but more noteworthy was the fact that it blew the dipstick out and sprayed oil over the top of the motor.

Today, I did a compression check and a leak-down test with the following results:

#1 124 psi 4%
#2 125 psi 3%
#3 134 psi 2%
#4 125 psi 3%
#5 124 psi 3%
#6 132 psi 3%
#7 134 psi 4%
#8 134 psi 4%

This is me now: :confusd:

In the past, it was always easy to tell which one was bad because it would be down 30 psi or more.

Also, I've read that anything below 5% leakdown is very good, especially if you consider my ring gaps are pretty wide (.025").

So what the hell is wrong with my motor???

 

What is your PCV set up ?

 

The PCV and routing is stock. The vent hose is described above.

 

ouch.. sounds to me like .025" is a little excessive on ring end gap, but thats just my opinion. does it blow the dipstick out at idle.. if so.. cracked ring or possibly cracked piston, but with those leak down numbers you have me kinda scratchin my head too.possibly if she is not blowing it out under vacuum, there may well be a leak between the intake manifold and the lifter galley, this can sometimes happen if your running heads that have been milled on an angle, slightly warped, or just bad gasket seating, and then put boost to them.. have you checked to make sure your intake bolts are tight, not accusing you of bad mechanics skills , but once in a while ya miss a bolt here or there on the second torque pass..? like I said this would definately show excessive crank case pressure and still show leak down and compression testing at perfect or close to perfect values! just a thought from em though take at how ya will!

Chris

 

Is the stock pcv system up to handaling all that pressure?...what if you went to so breathers in the Valve covers..., or maybe look into a GN set up, as that system up made for boost....

 

At idle, it pulls vacuum on the crankcase.

 

at idle, even if there was a leak between the manifold and the head on the lifter galley side, there would be vacuum from the leak as well. I'm just tossing out ideas for ya.. i know what its like hunting down these dumb issues that none of us like being plagued with.as mentioned abovve, have you checked the PCV valve? i know there isn't a whole lot to them but perhaps it is stuck open.. this would allow boost into the crank case as well.. when ya shake it is it still rattling?

also if you remove the intake if nothing else fails, there will generally gbe an oil trail from the mating surface towards the back of the valve with little or no oil on the intake runner side.. unless its NA and has oil being pulled at the throttle body still.. when i remove that line and run breathers on NA cars. the intake stay clean and pretty!

Chris

 

Put a brake booster check valve inline with the stock PCV valve and the intake.

 

I've checked the PCV and it still works, but the LT1 PCV doesn't seal off totally when you blow reverse pressure (boost) through it. I think Rooster is on to something.

Rooster, you talking about an LT1 brake check valve? Is that an Autozone part?

 

I'm REALLY interested to see this thread develop. I know some guys on their blowers just run with the PCV valve in stock position.

I have had repeated problems with leaking rear main seal. I ran without the PCV and just had a breather on the valve cover. I briefly had the stock PCV conected to behind the filter, but like you I thought that was too much oil to be flowing through the blower and intercooler.

This year I have purchased, but yet to install, an SSBC electric brake booster vacuum pump pulling through a check valve and venting to a puke tank. The plan is to keep a constant 14 -16#'s of vacuum under all conditions.

 

Its kinda a universal part. You cna find it in the help section. Its a heavy duty check valve.

The only problem is that its 3/8's by 1/2 ( if i remeber right) So you got to step back down to size

 

I am not sure I understand your pcv setup. You say vent hose but I don't know which one that is. The one on the pass. valve cover does not vent in a normal operating system. It pulls fresh air from the tb to be circulated throught the case.

My setup is this: pass valve cover hose vents to atmosphere now. The rest of the system is untouched. PCV is still in place with nothing hooked to the inlet of the blower. Pulls vacuum at idle and vents any pressure at wot. I have had no problems yet and don't forsee any.

 

You should at least be running the passenger side vent to before the blower.

Its supposed to be a circulation between high vaccum and low vaccum ports.

The port behind the throttle body is sometimes in boost and is not limited by a check valve.

 

I don't want any oil/mist being sucked up by my charger. That is why I scrapped the idea of trying to pull a vacuum. If I need vacuum at wot, I will add a crank evac setup via the exhaust. And yes, the port behind the t/b needs to be capped.

 

The vent hose that I refer to is the one on the pass valve cover and it was run to the intlet of the compressor, now to a bottle.