We've wandered off of Slindo's original question a little and I would like to post my experience with the dirttrack bike Chris and I and Jim ( XLR), prior to his un-timely death, run. The engine is a set of trapdoor K cases with KR cams, cylinders and heads. We use a sportster crank and rods with the double timken and needle bearing, and torringtons on both ends of the cams. We gear this motor for 6800 rpm and it occasionally sees as high as 7200. We are on our 3rd season with this set up and it has been dead reliable, knock on wood. I use a 1/4 speed pump and a .060 restrictor in the cam cover oil passage to the crank. I use 15-40 Delo 400. Also tightened up the scraper clearance with the crank. The most oil I will get out of the sump after a race is 1 1/2 ounces. I sealed off the primary from the crankcase and plugged the stock breather and put a breather hole and baffle at the rear top of the cam cover and run it thru a one way check valve. Adding this system dried up the few spots of oil seepage on the motor which makes me believe its running with a slight negative pressure in the crankcase.
I believe a lot of the oil consumtion quoted for these motors was because of the 50-60 weight oils used back then and one piece oil ring design that was common. When I drain this motor I get back 98+ percent of the oil I put in it. It shows minimal sign of burning oil in the combustion chamber and no smoke when on the track.