An engine develops maximum cylinder pressure when running at WOT. Some of that blowby will make it past the rings and into the crankcase. On a healthy engine with a working PCV, that crankcase vapor is drawn into the intake and burned. During WOT, there is very little vacuum, so a normal amount of crankcase pressure gets vented from the valve cover breathers.
On a very worn motor or one without proper venting, or very bad detonation, the blowby will be enough to push the dipstick out, cause oil leaks or otherwise find its way out of the crankcase. My current 400 is high mile and if I run it really hard, the dipstick comes out 1/2" and there is a mist of oil on the breathers.
How many miles, how is the PCV set up and any signs of detonation near WOT?
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I could explain all this to the girl at the parts store, but she'd probably call the asylum.
White '67 LeMans 407/TH350/Ford 3.89... RIP
Red '67 LeMans. 407/TH400/Ford 3.25
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