1994 Cobra 331 Dart Supercharged Excessive crankcase Pressure!! Help!

Apr 13, 2018
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Chattanooga, TN
#1
Quick Run down- Motor has about 600 miles on it and I am making about 14# of BOOST. Motor went through 1 rear main seal and the second one is leaking as well. Have come to the conclusion I have excessive crankcase pressure pushing oil out of the rear main!
Current setup- Running Turbocoupe PCV and one breather on passenger side valve cover
My shop wants to put another breather in the drivers side VC, but I'm thinking that's not a good idea!
Have bought a catch can, but have no room in engine bay...

Need some advice/help here getting sick of seeing oil on the floor on a motor that cost me a small fortune!!!!!
 
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jozsefsz

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Aug 11, 2013
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#3
Lose the PCV altogether (if you're running MAF you already have a vacuum leak of unmetered air with the driver-side breather - it's meant to be a closed system). Get a K&N filter breather cap like this: https://www.cjponyparts.com/k-n-oil-breather-cap-screw-in-1965-2004/p/OC12/ (assuming you have stock valve covers). If not, some other breather.

Boom you have a breather on the passenger side valve cover and no more crankcase pressurization problems. Turbo since 2009 with a dipstick that doesn't pop out anymore. :)
 

Noobz347

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#5
You can also use that breather to tie back into the PCV system and close it off again.

Lose the PCV altogether (if you're running MAF you already have a vacuum leak of unmetered air with the driver-side breather - it's meant to be a closed system). Get a K&N filter breather cap like this: https://www.cjponyparts.com/k-n-oil-breather-cap-screw-in-1965-2004/p/OC12/ (assuming you have stock valve covers). If not, some other breather.

Boom you have a breather on the passenger side valve cover and no more crankcase pressurization problems. Turbo since 2009 with a dipstick that doesn't pop out anymore. :)
Does yours have a check valve?
 

jozsefsz

Well-Known Member
Aug 11, 2013
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Cleveland OH Area
#7
If you have the PCV system closed as it should be (no open breathers) then a check valve (and / or TurboCoupe PCV) just serves to completely close off your crankcase while under boost - and while blowby is greatest. If the check-valve and TurboCoupe PCV are working perfectly, they won't allow boost pressure into the crankcase, but they also won't allow it to ventilate or draw a vacuum on it as designed. You're effectively turning off 'positive' crankcase ventiliation, but you're also effectively turning off any crankcase ventilation. Bye bye seals.

As mentioned before, if you have a breather on a valve cover, are still running PCV, and are using an MAF, then you have umetered air entering the combustion process which will mess with your AFR and possibly cause a rough idle. Not what you want under forced induction.

I've run for several years now without a PCV and have never noticed any fumes or oily mess (a decent filtered breather like the K&N cap I mention makes that a non-issue). Open ventilation also completely eliminates the sucking of oil and crap into your intake, and eliminates the need for a catch can. Just plug off the PCV port on the intake altogether.

Let it breathe. :) If you're emissions-conscious or are in an area with rigorous testing, this might not fly (my part of the world only has tailipipe testing, they don't care how you get to passing numbers). Your supercharger probably wouldn't pass either so a PCV delete is probably of minimal consequence (and can be re-installed for testing where it probably won't be put under great stress).
 

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