Originally Posted by LandSpeedRecord
A little accidental science. I raced a GSXR 600 for 3 seasons on 87 octane. One weekend i signed up for a 2 hour endurance race i had not planned to do and had to go buy fuel in a hurry. I could only find 93 octane so i threw it in and raced. The bike felt off but endurance racing is so physically and mentally hard i couldn't really tell. When i got home we put the bike on the dyno just to make sure it was ok and it was down on power from my last dyno session and I suspected the gas. We drained it completely and put my normal 87 pump gas back in and gained back exactly 5 horsepower on the dot. As described above octane is a flash retardant to prevent pre ignition in high compression engines. You will actually get the most horsepower from the lowest possible octane before pre ignition.
I'm glad people actually realize this... I've had countless arguements in other forums about putting in a lower octane fuel because it burns faster and puts out less emissions because of this... Octane is the fuel's resistance to burning, not the other way around like most people think. 87 octane will make more power and burn more completely hence the lower emissions output.
Luckily here in San Antonio we're not in an emissions county, but there are some counties in Texas that we do have to check for emissions when we inspect the cars. I've been telling people for years that if they don't have all their emissions components intact, the car can still pass an emissions test by running the Lowest octane fuel available and retarding the ignition timing as much as possible, even to the point where the engine feels sluggish (set to lowset recommended setting if the inspectors check the timing during the test, go a little lower if they're not required to check timing) , then drive it straight to the test station, let them run the testing, then switch everything back after testing is done. On turbocharged or supercharged vehicles, these Must run high octane fuels so I tell them when driving with the low octane gas in it DO NOT boost and it'll run ok enough to get there and back.
Posted something like that in one of the turbo forums I used to frequent and talk about starting a huge arguement from other members who didn't know against the few of us that do know...
The whole octane thing is basically use what's needed, and only go higher if it's needed... Anything more than what's needed will cause performance to go down and just drain your wallet faster.