You wont get a straight answer that fits all applications for just on petrol as its not that simple let alone on E85.

If you beleive that 8:1 was optimum for your engine on petrol though, the same engine will probably work very well at 9:1 on E85

Or keep it at 8:1 and you can run some more timing.


Depends largely on how hard you are revving it, if its high rpm power you want, then higher compression is king.