I have had two 347 motors, my current one has only been on the road for three weeks, but it seems to be doing fine so far...no oil leaks that is. My previous 347 lasted for almost seven years with two years being driven on street and it never leaked oil.
Both motors seem to burn a little oil all tho my current one is to new to tell just yet. I did not use the 'oil-control' pistons that Coast High advertises so that may account for me burning some oil, but it never seemed to really affect performance.
Whenever a motor is leaking oil externelly, then gaskets or sealer was not properly setup. My engine builder used Cork on the front and back of the intake, but also put a coat of thin sealer on the top and bottom of the cork, so far zero leaks.
As for the blowbye, I guess you are talking about oil vapor getting past the piston rings. That would have allot to do with how much pressure is building up in the crankcase I think. Just make sure you have valve covers that are adequetly ventilated and maybe a vacuum line for crankcase ventilation.
Just my two cents.
James
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