StarDiero75":h3rk3kxa said:
So with a 9.0:1 CR, what kind of dynamic CR should i be looking for?
That's a good question. I think a safe bet is 7.7:1. But you may be able to go higher and still run 87. With my 250 i'm around 8.2:1 dcr iirc and 9.5-6:1 scr @ ~25ft above sea level and I had a lot of problems with pinging under load. But that was timing, the carbs and the shift points of the stiff aod that has since loosened up. It was mostly timing. For a while I was afraid I had to keep the initial timing @ 8-10 and limit the vac advance with a machine screw. Running 91 to keep it in line. But I found that my dist weight was the problem. I was putting in 30 degrees w/ the mechanical advance real quick, add that to 12 deg initial and any remaining vacuum, vac can turn all the way stiff, and I saw 40-50 under load. I haven't tried running 87 since I finally fixed it but I'm going to. Now the vac canister is all the way loose w/o a limit. I'm running 13 degrees advanced and have all the power I need at my foot with no problems. ie... up a hill, foot down in low gear no ping. Or to lite up the tires on a whim
The 250 is more prone to detonation than the 200 b/c of it's long stroke. It's probably a safe bet to push it to 9.2:1 or better with a 200