erm, the 250 has 11:1 compression stock... That's not necessarily enough to Ping at lower elevations, such as yourself at 2000ft Decepticon. You could always try 87, and then 85... In CO, at 5,000ft + I have NEVER used more than 85. Heck, most of my friends with their super sports run 85... There just isn't enough air up here to ping or knock. Not sure that helps. I guess what I'm saying is experiment...