QuickSilver2002

To make a long story short, my dispstick bew out last night.

It is a c5 vette with all stock internals running about 9.5 psi with an ATI d1 blower. The car was finally running good and the AF was 11.5 and there was no KR at all. I’ve been relying on water/alky injection to protect my motor detonation and it has been working great.

I'm assuming I may have a cracked piston/ringland or something of that nature, but it raised allot of questions in my mind about blow by.

Here are my questions.

1. How much blowby is considered normal on a boosted car?

2. Is more blowby expected on a boosted motor compared to a NA motor?

3. Do you need a breather in the PCV on a boosted car? It seems that pressure from blowby has somewhere to go on a NA motor (the PCV ling going into the intake manifold), but has no escape on a boosted motor when under boost.

I have a check valve in my PCV line to keep the boost from pressurizing the valve cover, but I'm assuming this provides no breathing for pressure from blowby when the boost is on.

I’m still a little confused about exactly how the PCV is suppose to work. I have one line that goes to the intake manifold (it has a check valve and the normal PCV valve inline) and one that goes to the blower inlet area. The one going to the inlet is referred to as the PCV inlet. Can someone explain how these two different lines are routed down in to the crankcase? I’m having trouble conceptualizing how one is restricted to pulling air into the crankcase.
my question:

jimmyblue

iTrader: (11)

The "inlet" is before the TB and the "outlet" is
after the TB. Manifold vacuum draws blowby gasses
out of the crankcase and the area before the TB
is where the makeup air is drawn from.

Now, with 9PSI of positive crankcase pressure
(WOT = no pressure drop across blade and the
crankcase gets pressure-fed from both ends of
the PCV) it's not surprising that you'd pop the
cork. The dipstick design I'm sure did not assume
big positive crankcase pressure since there was
no boosted option on these cars.

I reckon this is also going to put your crank
seals to the test, these are also meant to have
zero or negative pressure.

Using a PCV scavenge pump (like an AIR pump w/
catch can, using the suction side to draw and
letting the presssure side blow free) would be one way to have negative crankcase pressure with
a positive manifold pressure.

Mike00FRC

iTrader: (1)

With the ATI, the inlet from the front of the throtle body is capped off and is re-routed from the airbox(not pressurized) to the front of the passenger valve cover.

The pressure could be from blowby, PCV line to intake manifold, or a combination of the two. Its probably the PCV thats the problem. It does not hold against boost. You can actually blow in to the manifold side of the pcv valve and air makes its way out, and I know I'm not putting 9psi through it.

I installed a check valve, but had to remove it. The spring pressue was too high and it had trouble opening under normal vaccum. As a result my LTerms shot up to +25 at idle with the check valve in place, so I went back to stock and haven't had a problem... but then again I'm only running 5-6 psi at WOT.

Might want to experiment with a different PCV valve or find a check valve with a lite open pressure.

QuickSilver2002

Thanks for the info guys, I meant to put this in forced induction, so I'm going to post it there also.

I have a check valve in my PCV line (that seems to work). I'm just confused as to why the dipstick would blow out if the pressure could have been going out the inlet side of the PCV (where there should have been quite a bit of vacuum when under boost).