Crankcase Pressure

[TWild]

Quick question,


Other than compression getting past the rings, what else can cause high crankcase pressure?


Thanks, TW

[Steve Wood]

boost past a bad pcv valve, intake leakage into the valley, and tired rings are the three causes I can think of...so the first two in answer to your question

[Norm340]

Would a RJC PCV be overkill http://rjcracing.com/product/rjc-pcv/.
Was going to replace mine and was looking at getting one.

[Steve Wood]

I think so

[TWild]

Steve,


When you say intake leakage into the valley, you mean like an intake gasket leak? The reason I'm asking is I recently had the intake off.


Yesterday I took the oil fill tube off the driver's side valve cover with it running, so I could look inside to make sure oil was pumping up through the pushrods and onto the rockers. I happen to rev the engine up while leaning over it and I noticed air coming out the hole in the valve cover (I hadn't noticed this in the past). The higher I rev the engine, the more air flows out the valve cover. It isn't a pulsating flow of air, it's a rather a steady stream of air. It feels like the air coming from a  blow dryer.


I'll check the PCV Valve when I get home.

[Forzfed]

If the head gasket is blown into the valley it would do that as well.

[1KWIKSIX]

Here's what I found out:
Make sure your valve cover breathers are vented and functioning properly.
I found out the hard way using some Mr. Gasket valve cover vents (into a catch can) that were defective.  Ended up discovering that they did not allow proper venting and would pressurize my crankcase, pushing out the dipstick and giving my undercarriage a free rustproofing with engine oil in the process!   
Replaced em with some new ones that did work properly and all is good! 

[TWild]

Thanks for the replies, now it's time to start checking it out! What I have found out is that owning one of these cars can be very enjoyable and very frustrating at the same time. I guess sticking with some basics and educating yourself is a good start. There are many people that are willing to help the new guys.


TW

[Scoobum]

Real world result with my own car. With the RJC valve...the idle BLM's rose from 118 to 128 using JUST the RJC valve. Steve can jump in and tell us about the RJC valve...and why my idle BLM's rose.

Catch cans...are nothing more than a band aid solution to worn rings.

Wanna see worn rings? Here I am from last October...link is below. The smoke you see...is from the crankcase pressurizing.. .pushing the dipstick up...and oil spraying on the DS header. This was the original engine from my car. I had Joe freshen it up with rings/bearings and balance the rotating assembly. The piston to wall clearnce was already max. We figured two full race seasons...but got four out of it. The dipstick started rising up about 2/3rds of the way through last season...thus the reason we pulled the engine this spring to inspect it. The engine is at Joes and I pick it up next Saturday...wit h it coming in at 235 cubic inches...and 9 to 1 compression.

https://www.youtube.com/watch?v=XG9Mu5nN8pM

[TWild]

Thanks Scoobum and another fun video! What was the loud pop while you were doing your burnout?

[Scoobum]

Thanks Scoobum and another fun video! What was the loud pop while you were doing your burnout?

Sounds like it's sneezing. Turbo may have had a cold that day...

https://www.youtube.com/watch?v=QFjkrBgHMCc

https://www.youtube.com/watch?v=gOoZOjB7Gyk

[Steve Wood]

yes, I meant the intake was leaking into the valley.  Also, Forzfed is right..blown hg into the valley side

Lotsa people have posted similar with the check valve.  I see no problem with it on a race car at w.o.t.

For a driver, I would prefer to leave it out.  Highway Stars has both the original nos factory pvc and the cheaper, Standard replacment valves.

[TWild]

Thanks guys.

[TWild]

When it comes to an intake leak, I have a couple of more questions. I noticed that some guys get rid of the pcv valve altogether and some install a breather in the intake (where the pcv valve would normally go). Why wouldn't that create a vacuum leak? What effect would an intake leak have on O2 millivolt readings, blm's etc...?

[Steve Wood]

First, the pcv should be a sealed sysem for most efficiency. The cars originally had a baffle in the end of the passenger side valve cover that was connected to the turbo compressor side inlet.  The turbo would pull oil vapors and some oil out of the cover so we disconnected the tube and stuck a small filter in the end of the cover.  The pcv valve is inserted into the intake next to the plenum.  I have never seen a breather stuck into the pcv hole but if it can be done, I'm sure someone is doing it.  The turbo pcv for the turbo cars was calibrated differently from the regular cars.

Also the oil filling side was capped off but we have stuck a breather in there in many cases,  So, the pcv system does not function as well as it should but it's better than nothing I suspect.  If you don't have a functioning pcv, then there is no mechanism for sucking the corrosive vapors out of the engine and they contaminate the oil faster than normal.  This means we should change the oil more frequently=maybe every 1500 miles.

Race cars change it after most meets to see what is found in the oil...so pcv is not needed.

An intake leak will allow boost to be expelled into the engine and, under non boost operation, will allow unmetered air to be drawn into the engine and that will show up as leaner than normal operation

That may be seen in higher than usual blms at cruise.