just breaking in 11.5.1 je piston what fuel octane should i use at 3900 elevation ,91 octane is all they sell here, or what octane booster should i try,ther is a place that sells 110 racing fuel i do think its to much,

 

HPR recomends 93 octane for their 11:1 piston... at your elevation I would think 91 would be right at the limit. Do some searches OMR posted a elevation to octane ratio... also I think Hightower was running that piston for a while, he might have some better input. Good luck.

 

im at about 1500 or so and i can just barely squeek by with 93 octane. wish they sold 95 or 98 around here.

 

Buy 5 gallons of the 110 and mix 50/50 with the 91. Better to be on the safe side of things. It will cost more in fuel, but peace of mind takes cash [img]i/expressions/face-icon-small-smile.gif[/img] I will more then likely be running a 75/25 mix of 110 and 93 at sea level on mine, maybe even straight 110. But that is me.

 

You should be fine with 91 at that elevation. I'm run 91 at sea level without any problems

HPR 14:1 with thicker gaskets (11.7:1) effective ratio w/HR3 cams and Vortex CDI on #1. I was skeptical at first but she shows no signs of detonation.