You need to run oils that are certified for air cooled engines. In most cases those are racing oils or aircraft related. I'm not sure without looking it up , but I think it's SE rating. Valvoline Racing oil fits, Castrol GT, Royal Purple , Aero Shell, and Lucas oil. I usually run Valvoline Racing oil. 60WT in the shovel 20W50 in the Evo because it's readily available. I've had good luck with Castrol GT1. It comes in 70 wt which is good in 100+ temps. The evo runs great in any temps on the 20W50. Occasionally I add some Marvel Mystery Oil to clean out the system. Royal Purple claims to run cooler than any other oil. That's an attractive claim. I have rebuilt motors run on Harley oil, and Valvoline, and the ones run on Valvoline care much cleaner inside than the other brands of oil. I consider that a good sign.
We're taking a ride to Deadwood SD. next week (1500 miles round trip) for a family reunion and I'm going to switch to the HD Synthetic to test it. A lot of my customers run it and like it very well. At 10 bucks a quart it had better do very well. I'll post my thoughts after I get back.
Thanks Curt, that was very informative and exactly what I was looking for. I really appreciate it.