it's not worth the "extra performance" or the more even/slower fuel combustion with a higher grade octane fuel than recommended for your car cuz all you're doing is dirtying up your cat...i wish i could use 87/89. stock i would but ever since i advanced my ignition timing a couple degrees i wouldn't dare.
dynamic compression also helps dictate what grade of fuel you need, not to mention, the cam profile, if you have alot of overlap, you can bleed off. I ran 11:1 compression with an aluminum headed motor everyday, but had the cam and gears to make up for it. Now if you have a stock engine, that only ask for 87 octane, using 93 will not help.
Well I have a Honda NX 250 motercycle, and it redlines at 9,000 rpms I'm not sure what is recomendend for it but I will check. I just wondered if 87 or 89 octane would be better for it. And are there any cheep mods that can help boost the performance of a 250 motercycle?