[bobzdar]

Originally Posted by Skip Fix

To say because Pontiac used a wide lobe sep in their 10:1 motors they were designed for 87 or even 93 octane is way off, what was even regular leaded back in the 70s? I think Sunoco 260 was like 102 at the pump. A little different in a 10;1 than tghe ethanol 87 stuff you might get now.

I don't think anyone was saying they were designed for that, but I think they're more tolerant of running 93 than if they had a tighter lsa?

Racing wise, a tighter lsa probably works well particularly if you're running a really narrow rpm range - which is Dude's area of expertise, so I think he would know. I know what's worked well for me and what hasn't - and I have 2 cars at 10:1 that will run fine on 93 octane and both have a wide lsa and are using factory parts similar to the OP, but then there's little margin for error. Based on my experience with a shorter duration, tighter lsa cam I know they would detonate themselves to death if that were the choice, I had to run 91 in an 8:1 engine with a small cam and it didn't run very well.

This is why I suggested picking the compression ratio after the rest of the combination was thought out, as the cam can have an influence. It seems like for his purposes and parts a 10-15cc dish will be ideal so fuel quality won't be a concern as 2 or 3 people have suggested. You don't want to worry about it on a street car if you don't have to. I don't know that going lower than that would gain anything other than the ability to run cheaper gas, which wasn't mentioned as a concern.