What is too much blow-by

[5timesturbo]

I rebuilt my engine with 9:1 pistons and started it up and I’m not sure if I’m getting too much blow-by?!? If I plug the vent case hole in the valve cover I feel the pressure building and when I let it go….I can hear the pressure release….kinda like a blow off valve but not as as extreme. It’s doesn’t come from the oil stick hole unless I plug the valve cover hole…. I thought I put the pistons in right but I want to make sure before I dyno the car and try to get it running at high horse power levels….so can anyone tell me if they experience pressurizing blow by at the valve cover hole??

[turbodan]

I would quantify blowby by monitoring oil loss through the breather. If it's not blowing oil out its good. You could also test leakdown to get some actual data, after probably 1500 miles to break it in.

There will always be cylinder leakage. Even one or two percent is going to be a noticeable volume of vapor. Excessive leakage creates a high volume of blowby gases which funnel through the breather system so quickly that they pick up more oil than the baffling in the valve cover can catch.

[5timesturbo]

The engine is brand new so I’m not see white smoke….only black smoke because it’s running rich and the tune needs to be adjusted. I’m gonna do a pressure test on the cylinders tomorrow and see how close the pressures are….

[turbodan]

I would drive it for a while before you do any diagnostic tests. Break it in, monitor oil level along the way and don't worry too much.

[gadget73]

might want to get that excessively fat tune fixed sooner rather than later. Too much fuel will wash the oil off the cylinder walls and cause premature wear.