I am running a 383 stroker motor, and for as long as I can remember, at about 6200 RPM my engine builds up enough crancase pressure to pop the dipstick up about 2 inches and blows a puff of pressure out the dipstick hole.
The engine has about 4000 miles on it since the last complete rebuild, it popped the dip stick before the rebuild as well as after.
I have recently replaced the valve covers with a set with 2 breather caps, so I know it is getting pleanty of ventilation at the top end.
At any thing less than 6200 RPM, there is no problem.
The engine is making 362 HP at the rear wheels.

Any suggestions?
:seeya

 

Are you using any form of vacuum for crankcase ventilation(PCV VALVE)? If not you will need to have a breather on both valve covers, and it is best to hook up either a pcv valve or at least a hose from valve cover to your air filter box. What type of head gaskets are you using? I ran into a set, I believe they were victor, that had very small breather/oil holes in them. They actually restricted the crankcase's ability to breathe(I had restricted the holes in lifter valley so it wasn't breathing much there either) and also slowed the oil return. I was having so much crankcase pressure, it actually blew the front seal in the timing cover! I did a cyl. leakdown test, and rings were sealing fine. After several changes to valve covers and pcv system, I tore the engine down to check cyl. bores at the very bottom of cyl. Still nothing. After talking to several engine builders and back yard guru's, I compared the head gaskets to a new set and found most of the holes were smaller. I changed to different head gaskets, replaced everyting else, and no more pressure problems! :D First off, check your pcv system then I'd do a cyl. bleed test to see if your rings are sealing good. If these are all ok and you can't seem to find anything, pull the valve covers and see if anyplace you can pass through the head into the lifter valley that the gasket is not closing that area. Hopefully this helps. :seeya

 

you're saying it's popping out the dipstick even with 2 breather caps? and this popping out is accompanied with a puff of smoke?

i'd say your rings aren't sealing very well at all, then. i can see that with a sealed crankcase with just a pcv, but not with breathers.

on the other hand, if the seal is that bad, i'd expect some oil saturating the breather cap filters. how clean are those?

try a leakdown test and see how well those cylinders are sealing.