hello new to the site as i also posted in the chrysler section, i have a 67 Belvedere, 383, 727 auto, i have done a comp' test and have 148 lbs on all cylinders except # 3&5, 3 has 130 5 has 142, i understand that 15% difference is acceptable, other guys say it's 15 lb, I have cracked 2 valley pans within 1500 miles, i also am leaking out of the timing cover, gaskets been replaced 2x this year. oil blows out of the dipstick tube as well. could this be associated with blowby on the 2 weak cylinders  

Ive always said 20 lbs comp.variable across all 8 in 5 or less rotations of the crank per cyl.However if 3 & 5 are side by side you may have the head gasket blown between them,causing compressed gases to b forced in to the crankcase as the piston at its side comes up.This will sometimes hide from a comp. test.and can create enough crankcase pressure to expell the dipstick.  

Is your pcv valve stuck shut?? this will also cause your symptoms.Take it out and see if it rattles.If it dont,replace it,if it does,see if the hose is collapsing while the engine is running.check hose connection on intake/vally pan/carb(I dont remember which it connects to)Getting old stinks.See if its plugged with carbon/oil crud.If these check good,then yeah you might have a bad head gasket(you would have coolant/oil consumption problem with either)It may be blowby due to weak ring seal on the two weak cylenders.Pull the breather and see if it is puffing oil or smoke.How many miles are on this engine?? if its high miles,some blow by is to be expected.Your compression test showes a fairly balanced wear pattern.General rule of thumb is 20 percent difference between cylenders as acceptable.Do you run this engine hard?(sustained high RPM)or do you notice the problem at low speed or just plain flat out allways?Either way it may be time to dig in and freshen that beast up.Good luck.  

pcv, hose, head gasket, are all good/ new, no coolant usage, oil leaks but does not burn, motor has 80,000, it has a 3/73 rear end, sohte rpms are around 3,000 on the highway, not terribly high, i don't pound on the car, but i do love to drive it, another thing i noticed, when i'm driving it at a constant speed for awhile and then decelerate, when it gets down to around 10 mph and 1000 rpm you can hear the valley pan pop like an old oil can, i'm pulling the motor and rebuilding it, i'm so damned tired of these oil leaks.  

You should do a leak down test to verify blow by source before you tear it down.But yeah considering cars age it is probably time.Good luck.  

i took the motor out, had a broken ring on #3, i had the block decked and bored i put 'er back in and she runs great, no blowby.