desmoc

Hi,

Please tell me, what crank case pressure in Porsche is?
Is it the same as blow by from rings?
What is it good for?

Many Thanks in Advance.

porsche52

1.Crank case pressure = Combustion gases in crank case via blow by.
2.What is it good for? Nothing... Robs a couple H.P, Contaminates oil.
3. PCV valve!! heard of that before? Positive Crankcase Ventilation valve. Porsche uses a Air/Oil seperatior on the N/A cars (9X6 and (9X7) and on the Turbo (996/997) they vent the crankcase into the oil tank and scavange through a fixed orifice into the intake. Now the GT3 actually has a negative pressure in the crankcase to free up a couple of H.P. And that is IMHO why they have rear main seal issues and the Turbo/GT2 do not. The N/A engine in the 996,986,987,997 have cut-outs(notches) at the bottom of each cylinder to reduce the H.P. loss caused by compression of the air below the piston during the downward stroke (intake and power).
4. Why do you ask? Just curious.

desmoc

I was Just curious. Because every time RMS issue comes up, dealership checks the crank case pressure.
One more reason not to buy a NA 996 or 997.
Thank You for your reply.

porsche52

Hum... OK? Every internal combustion engine has crankcase pressure. I think you are a little off in your logic. IMHO RMS issue's are more due to seal design and construction, crankshaft dimensions, manual gearbox opposed to Tiptronic, seal installation, etc. The new PTFE seal has been very good. RMS issues on the NA 9X6/9X7 are nowhere near what the were 3-5 years ago. Now like I said, the GT3 is a different animal all together.

haulinkraut

Maybe the dealership is verifying that the seal is the defective part and not a result of another issue. Excessive case pressures/vacuum could cause a RMS to fail early, no? Other cars can go through valve cover gaskets due to excessive gas pressures.

Robeguyl

porsche 52, looks like you know your stuff. I have a porsche 997 carrera 3.6 - 2005 with 150k on the clock. It has recently blown out the brown cylinder head plug, in fact it did it on a road trip 6 months ago (8k miles since then). At that time i bought a new plug and its been good, until now. When i run the engine, after re inserting the plug but remove the oil filler cap its breathing out from the filler cap, so alot of pressure exhausting out the filler tube. put the oil cap on and the brown plug blows out with a loud bang (Passenger side of cylinder head).
I replaced the AOS a yr ago, including all the pipes, (horrible job) so im really hope its not that again.

Any ideas why i have this back pressure? Thanks so much.

Carlo_Carrera

Dude, this thread is 13 years old and the last time Porsche52 posted here was 12 years ago.

Dock

porsche52's latest post on Rennlist was in 2010.

993GT

just add a 3 or 4 stage Autoverdi and suck that crankcase right up