91 octane

[RabiDIntegrA]

I was wondering if it's bad to always put 91 octane in a car that's basically stock? I know all the vtec engines need to have 91 octane or higher. But what about the non vtec engines like the B18B? Would I be better off putting in 89 octane or 90 octane. Would I get better MPG if I would 89 or 90? Cause lately I have been getting shitty gas mileage.

[Gen3Project]

You would be better off running the octane the owners manual suggests. Otherwise you are throwing your money away and loosing performance.

[RabiDIntegrA]

even if I have minor engine mods like header and exhaust?

[Gen3Project]

Only if you increase your compression will you need a higher octane. Bolt-ons will not change your compression.

[lshybrid195]

if you have a stock b18b you could use 89 octane but yes on vtec motor it is recommended that you use 91

[CRVTEC0WNZJ00]

I used to always run premium in my B18A1 even when it was just an intake and exhaust. Its just a cleaner burning fuel I believe. Yes VTEC cars all run premium.

[Gen3Project]

What makes you believe that it is cleaner when used in an engine that doesn't need it?

[White98LS]

87 or 89 octane will burn more efficiently and completely than 91. All higher octane does is make it MORE DIFFICULT to ignite the fuel, so you don't get pre-detonation with high compression, advanced ignition timing, etc. So you may very well be paying more money for less performance and gas mileage.

I used to run 2 degrees advanced timing and 92 octane, but a couple months ago I switched back to stock timing and 87 octane. Very very little difference, and seems like a bit better mileage. On stock timing and your low compression there is no benefit at all to running higher octane than what you need.

[CRVTEC0WNZJ00]

I just think its a cleaner fuel is all, but now I have to run premium only anyway.