Dand88944ls1

I have a stroker 383 Ls1 with ARE drysump in a track only car. I recently got it on a tuning dyno to check the tune. During the tune I had a geyser of oil and air blow out of the breather catch can. For a bit of history, the last race of the year last Oct, the car didn't show any signs of excessive blow-by and was not pumping oil out the breather.

I stopped the tuning session after a clean up and then a gentle run back up the rpm range showed there was going to be a lot of air and oil coming out of the breather at higher ~4000rpm.

I did a cold dry compression check and a leak down check with these results. The car is at 2200ft altitude.
cyl comp leakdown%
1 158 9
2 152 8
3 155 12
4 150 12
5 148 15
6 150 12
7 148 12
8 152 9
I am not certain what my compression ratio is but expect it to be high 11. I didn't build the engine. Any input on the health of the motor or what might be causing the high volume of air/oil coming out the breather is appreciated. The oil tank is filled at about the 1/2 mark and the engine was not blowing blue smoke during the dyno run nor last year at the track. The oil pressure was 3.8 bar.
Thanks

slowride

iTrader: (3)

Lots of these stroker motors seem to have some blow by when built on stock block with short sleaves, etc. High compression might not help that along with camshaft, etc. One thing I think might be going on is oil pooling in the valve covers and under blow by conditions it gets pushed out the breather hose as the gas is trying to escape, but the oil is in the way.

I'd get some oil in my breather tank when road racing, but figured it was due to high g's in the corners not allowing the oil to travel back to the pan. I did think about running some restricted pushrods to see if I can keep some of the excess oil out of the valve covers and back into the pan where it belongs.