Abe,

You may have the same problem I had.  I was blowing a lot of oil out the crankcase breather too.  My Performance Engines IO-550 had forged and coated pistons that expand at a different rate than the ECI cast pistons with a steel band for the compression ring land.  The compression rings had worn so much in the lands on all 6 pistons they would “flutter” when power was reduced.  The engine had about 40 hours TT.  To test the pressure in the crankcase breather, tap a manometer into the breather about ½ it’s length or closer to the engine.  My engine would show zero pressure on the ground regardless of power setting.  On the takeoff roll still zero.  At about 120 knots it would jump to 5” and stay there until power was reduced.  When MP was slowly reduced to about 18” the pressure in the crankcase vent line climbed to over 30”.  That was when all the oil was being blown out the breather.  The prop was unloaded just enough to allow the worn rings to flutter up and down in the ring lands and allow combustion pressure into the crankcase.  

A mechanic and I spent weeks chasing this problem with ideas from many sources.  The good folks at ECI (Engine Components Inc. of San Antonio, mfg of the cylinders) had it figured out as soon as they heard the symptoms.  ECI honed my cylinders and gave me new cast and steel banded pistons with rings at no charge and within 48 hours.  We got the cylinders back on just in time to fly to Oshkosh.  The belly is clean and my catch tank for the Andair Air-Oil Separator is bone dry. 

Steve Colwell  Legacy  N15SC