i just swaped my 1998 305 crate motor for a re built 1979 350 and the 350 has blow by...the 350 ran fine with no probs...all i did was used my intake off my later vortec motor... the valve covers on the 350 build up with compression and i have to vent them good...the motor dont smoke or burn oil...any idea?

 

Is this engine a very fresh rebuild? If so then a bit of blow-by is normal until the piston rings seat. Pull out your dipstick and smell the oil on it. If it smells like gas then its blowby. If after about 1K miles, you still have this issue then i would venture to say that this engine was not broken in or rebuilt properly and the cylinder walls are wiped out. You can try this. Get it warmed up to operating temp. then take it out on the highway and dont flog it but accelerate hard up to 60MPH, then let off until you drop down to about 40, then accelerate hard again up to 60. Do this about 4 times and those rings should scrub in. Dont beat the crap out of it just accelerate hard like you are merging with traffic and this butt hole in the slow lane wont let you merge. What this does is load the rings and presses them against the cross-hatch in the cylinder walls. This makes them seal against the cylinder walls properly.