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Crankcase pressure
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aharris05
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1968 Chevrolet Camaro

PostPosted: Thu Nov 20, 2014 1:37 pm    Post subject: Crankcase pressure Reply with quote

What are some causes of excess crankcase pressure, and what can I do to correct it? I have a newly built motor, that blows the dipstick out at about 6000 RPM. Here's the basic info - its an .030 small block 350 with Eagle stroker crank. (=383ci) speed-pro hyper pistons, flat top 2VR, Mahle moly rings. M55HV oil pump & Moroso pickup, 6 qt pan. 64cc Sportsman 2 angle plug heads, Elgin flat tappet Hyd. cam, 292 int, 300 ex, .488 lift with 1.6 roller rockers, .041 felpro head gaskets. Torker 2 intake, 600 edelbrock carb, HEI dizzy.

CR should only be around 10.5:1, running 93 octane pump gas. Oil pressure is 80psi cold, about 50psi once its warmed up.
I put a differential pressure gauge on the dipstick, and its reading 1.5 to 2 inches negative pressure until I whack the throttle to 5500-6000, then it slams to positive 2"! I do have a breather on one valve cover, and a PCV on the other into the carb base/manifold vac.

Do I need an evac system? Maybe stock pressure oil pump? Windage tray? Please help!
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clay
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1972 Chevrolet Nova

PostPosted: Thu Nov 20, 2014 4:36 pm    Post subject: Reply with quote

I wouldn't think 2" would blow a dipstick out. Was this test just a quick rev or under load? Which breather do you specifically have? Some of them leave a lot to be desired as far as flow but look pretty. You can look at PCV flow too. At w.o.t it won't really be sucking but it does provide a path for pressure to escape. Sounds like a leak down test is in order too. The only engines I've had the dipstick blown out of were either shot or detonating itself to death. Clay
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aharris05
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1968 Chevrolet Camaro

PostPosted: Thu Nov 20, 2014 9:11 pm    Post subject: Reply with quote

I mostly see it happen under no load. The pressure may be more than 2", that's the max reading on the gauge. The point is, it spikes for some reason at the higher rpms. I just have a Mr Gasket chrome breather, on alum. valve cover with no baffles. Theres evidence of oil out the breather cap too. I guess the primary cause for pressure in the bottom end is blowby, I will have to try a leakdown test.

Do I need to bother with the PCV, or maybe take it out and replace with additional breathers in the valve covers? Theres only about 9 inches vacuum at idle.
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clay
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PostPosted: Thu Nov 20, 2014 10:04 pm    Post subject: Reply with quote

Even if you don't have the best PCV valve that isn't your problem. If I were in your shoes a leak down test would absolutely be the next step. If you're giving the pressure readings as inches of water pressure it really should pull more than that at idle. I've never actually measured it but just plugging the breather hole by hand on running engines I've felt some pretty good suction build up. Clay
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af2
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1933 Willys Coupe

PostPosted: Thu Nov 20, 2014 10:19 pm    Post subject: Reply with quote

clay wrote:
Even if you don't have the best PCV valve that isn't your problem. If I were in your shoes a leak down test would absolutely be the next step. If you're giving the pressure readings as inches of water pressure it really should pull more than that at idle. I've never actually measured it but just plugging the breather hole by hand on running engines I've felt some pretty good suction build up. Clay


As Clay said, I would hope you have more inches of vacuum at idle. The power valve will be open otherwise.
At 2" positive will never blow the dip stick. You might be more like 2 ' lbs which is wrong. Do a leak down....
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aharris05
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1968 Chevrolet Camaro

PostPosted: Thu Nov 20, 2014 10:33 pm    Post subject: Reply with quote

It could be that the at high RPM, the WOT lets the PCV close (no vacuum, so the spring closes it). That could be the cause of the spike in pressure I saw on the gauge. Especially if the breather cap is restricted, or too small to allow the volume of pressure out. Can you recommend a good push-in breather?
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Fri Nov 21, 2014 12:18 am    Post subject: Reply with quote

what oil are you running? sounds silly but sometimes the oil can screw with ring seal. ive encountered this phenomenon two times in 20 years. unlikely but it does happen. other than that.... what they said. leak down test!
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aharris05
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PostPosted: Fri Nov 21, 2014 11:28 am    Post subject: Reply with quote

Theres 9"Hg manifold vacuum at idle. in the crankcase, i measured with a low pressure gauge, -2 in water column (not mercury). running 10W40 pennzoil with Lucas additive.
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clay
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PostPosted: Fri Nov 21, 2014 9:12 pm    Post subject: Reply with quote

Without baffles in a valve cover you are probably going to have oil coming out of about any breather you run. You might as well make some baffles to go inside your valve covers. I run a K & N style clamp on breather from our local speed shop. I had to take the baffles out of these valve covers but the stud girdles are pretty close to the valve covers and shield the breather outlet pretty good. I originally made this offset breather pipe to clear supercharger plumbing but it helps with oil control also.

Mostly keep in mind you need to give oil droplets something to run into and not have a line of sight to the breather. Clay

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10sec.et
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PostPosted: Sat Nov 22, 2014 1:28 am    Post subject: Reply with quote

doesnt sound like anything weird with the oil. might need to ditch the pcv and run some good valve cover breathers. like Clay said... you need baffles if youre going to use them. i would still do a leakdown.
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Knarley Darley
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PostPosted: Sat Nov 22, 2014 11:37 pm    Post subject: Reply with quote

The cam is pretty big ( duration) so the 9" at idle is probably about the best you are going to get. You just have to make sure the power valve is closing at idle probably a 7.5 or less. I have had engines do this before when they were new, and they got better after they had a few miles on them, like 500-2000 miles of break in. If you can I would run a 5/8" or bigger diameter hose from the breather into the base of the air cleaner. Basically a stock set up which should flow enough air to keep the dip stick in. The other thing is check to make sure the dip stick is not hitting the crank, and being knocked out because of the mechanical contact. How many miles are on this engine?
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af2
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1933 Willys Coupe

PostPosted: Sun Nov 23, 2014 6:41 pm    Post subject: Reply with quote

Knarley Darley wrote:
The other thing is check to make sure the dip stick is not hitting the crank, and being knocked out because of the mechanical contact. How many miles are on this engine?


Excellent call!! If the down tube is missing it could very well happen.
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aharris05
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1968 Chevrolet Camaro

PostPosted: Mon Nov 24, 2014 1:33 pm    Post subject: Reply with quote

Knarley Darley wrote:
If you can I would run a 5/8" or bigger diameter hose from the breather into the base of the air cleaner. Basically a stock set up which should flow enough air to keep the dip stick in. The other thing is check to make sure the dip stick is not hitting the crank, and being knocked out because of the mechanical contact. How many miles are on this engine?


This motor is basically brand new. less than 50 miles on it, but the car isn't street legal, so I can only run it at the track. It was spraying oil under the hood during burnout, when I found the dipstick pushed up about 4 inches, that's why I suspect crankcase pressure. I wasn't running an air cleaner, I can add one and try plumbing the breather to it like you suggested.
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clay
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PostPosted: Mon Nov 24, 2014 4:31 pm    Post subject: Reply with quote

Please get an air cleaner on it. It'll save you money in the long run. How long is the dipstick tube? If it's what I call the "normal" style that is about 8" long vibration probably isn't a problem but if it's some different long style that isn't supported at the top vibration is another possibility. I'm leaning toward ring seal because of the lack of more crankcase vacuum at idle. Clay
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Knarley Darley
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PostPosted: Mon Nov 24, 2014 9:19 pm    Post subject: Reply with quote

I did not realize it was a track car. In that case a cheap fix would be to weld a couple pieces of pipe into the header collectors at a 45degree angle, threaded for a couple of smog tube check valves, and run a hose from each valve cover to the check valves.
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