compression and octane question

[rotarex]

would like to know whats the highest compression piston one can use before using 89 octane, or is there more to the question im not asking?

the goal is more power without using higher octane than 87

[lexusmech]

Really I don't know as far as hands on...but to my knowledge..9.5:1 is really pushing it, and you'd want to stick to name brand 87. And I'm pretty sure you would have to run conservative timing. For not much more 89 octane would be a good choice too. I know though if you're concerned with octane/price then 91 is out of the picture.

[rotarex]

i think 9.5:1 is still low Honda's got 9.9:1 on some civics, but i been running through alot of sites and checking specs on all vehicles and i think the answer is 10.5:1, i came up with that answer from looking at a Honda civic 2007 they got that, but i think a proper tuned ecu. and i think there is way more to my answer just haven't found out yet,

but yet their s2000 is 11:1 and takes 91 octane so don't fully know yet

[Pineapple]

Like you said it depends on lots of things. Combustion chamber design, coolant path, piston material/coating, fuel and timing tuning, present of knock sensor etc.