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Old 08-11-2012, 11:51 PM
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Blown bbc too much crankace pressure

I have a 454 HO crate motor, fresh rebuild chrome moly rings with 24 thousand ring gap,10/71 with (2) HP 4150 carbs, comp cam blower cam, solid roller lifters, roller rocker, I have moroso evac system from the breathers run down into the headers. I am pushing my dip stick out and pushing oil. when I put my foot in it it will blow the breathers out of the valve covers. Compression is 95lbs per cylinder. cam is a custom blower cam 650 lift not sure duration don't have spec sheet now, 114 separation. 400 turbo, 456 gear. I am stumped I don't want to run it and break any rings or worse. I NEED HELP Why all the pressure. Engine runs great doesn't smoke was broken in properly, plugs look OK still a little lean with 90 jets in back and 86 in front.

Thanks John

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Last edited by johnaiello; 08-12-2012 at 12:18 AM.
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Old 08-12-2012, 12:54 AM
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Quote:
Originally Posted by johnaiello View Post
I have a 454 HO crate motor, fresh rebuild chrome moly rings with 24 thousand ring gap,10/71 with (2) HP 4150 carbs, comp cam blower cam, solid roller lifters, roller rocker, I have moroso evac system from the breathers run down into the headers. I am pushing my dip stick out and pushing oil. when I put my foot in it it will blow the breathers out of the valve covers. Compression is 95lbs per cylinder. cam is a custom blower cam 650 lift not sure duration don't have spec sheet now, 114 separation. 400 turbo, 456 gear. I am stumped I don't want to run it and break any rings or worse. I NEED HELP Why all the pressure. Engine runs great doesn't smoke was broken in properly, plugs look OK still a little lean with 90 jets in back and 86 in front.

Thanks John
Are you positive you have "chrome moly" rings and not moly inlay or plasma moly rings or some other type of ring material?

In any event, upside down second rings will pump the crankcase nice and full of pressure.
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Old 08-12-2012, 07:48 AM
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Its best to do a leak down test at TDC. Is this an original bore block ?? How were the cylinders preped ?? Was it honed with a plate using a good hone VS a rinky dink one? What finish did they use on the cylinders?

No such thing as a chrom/moly rings and with any performance engine ring seal is key.
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Old 08-12-2012, 08:30 AM
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I assume the engine is a low compression 454 with around 7.5:1 cr.

So, with a blower cam (wide lsa) and a later intake closing point from a bigger than stock cam, I would say 95-110 psi with a compression gage is about right.

Furthermore, compression gages are not known to be accurate. I have 2 gages that are the same make and model and one reads 20 to 30 psi more than the other one. But, the difference between cylinders is what you need to look for, no so much the number.

Maybe the header evac system isn't working or the rings haven't set yet??

Tell us about the block prep, pistons, and clearances used.
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Old 08-12-2012, 09:23 AM
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Block work

First Thanks for the response.
Rings are all in correct, I assembled the motor, it has Manley stainless steel valves. Block was done at a very reputable shop. 95 lbs is what I have researched to be the correct compression reading with 114 lobe separation.The bore is stock 4.25, original forged aluminum pistons 8.75 compression. Sealed power E233K Moly rings. Harland sharp stud girdle. I took it to the strip and it ran bad too lean, I broke the #7 exhaust valve. I replaced the spring and I don't have a leak down tester but left the compression tester on each cylinder for at least 1/2 hour no loss of pressure.
Thanks For the help.
John

Last edited by johnaiello; 08-12-2012 at 09:32 AM.
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Old 08-12-2012, 10:24 AM
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Quote:
Originally Posted by johnaiello View Post
First Thanks for the response.
Rings are all in correct, I assembled the motor, it has Manley stainless steel valves. Block was done at a very reputable shop. 95 lbs is what I have researched to be the correct compression reading with 114 lobe separation.The bore is stock 4.25, original forged aluminum pistons 8.75 compression. Sealed power E233K Moly rings. Harland sharp stud girdle. I took it to the strip and it ran bad too lean, I broke the #7 exhaust valve. I replaced the spring and I don't have a leak down tester but left the compression tester on each cylinder for at least 1/2 hour no loss of pressure.
Thanks For the help.
John
I can tell you a stock bore block once the heads are bolted on that 454 block distort alot and if you getting blowby I can see why. OEM block are frail compared to a Dart block.

Go over this link and you can see what I am talking. Putting boost pressure to the cylinders amplifies the poor block prep.

http://www.camaros.net/forums/showthread.php?t=58964
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