Hey folks, I have a 07 Fit Sport with some mild modifications on it:
T1r Intake
Tanabe Medallion axleback exhaust
Megan Racing B-Pipe

I autocross my Fit and I currently put the factory recommended 87 octane in the car. My last car required 94 due to the massive turbo I put on it, and I'd like to keep running 87 if possible. What I'm wondering though is at what point do you need to up your octane on the fit? I know that if you put a supercharger or turbo on it you have to bump up to 91, but I'm thinking that during a hot day on the track, perhaps I should be running 89 with my current mods. I haven't dyno'd the car, but I imagine my powerband has moved up and I'm not entirely sure the stock ECU knows what to do with it. It would be a shame to find out that the ECU is taking timing out because I'm detonating on 87.

Thanks for the educated responses

 

More octane is always better.....87 burns much faster in the compression chamber than say 93... thus robbing you of "some" power and mpg. Before you car detonates the ecu will pull timing, with that said your current mods will not affect the ecu in such a way that would cause it to pull timing because of the fuel your using. Start introducing more oxygen via SC, turbo, nitrous and you will run into problems using low octane.

 

More octane is not always better. A higher octane just doesn't ignite as easily, hence why it causes less detonation. Thanks for the info though, much appreciated.

 

In what kind of application short of a pure ethanol based (e85) high boost application would less octane be beneficial? Remember any internal combustion engine can run on 93+ but not vice versa. Or at least not for the long term. Example my Honda will run just fine on either 93 or 87, but my wife's BMW's dash will light up like a Christmas tree if you use 87 for a good amount of time, and in fact will shut itself down . So in short octane is always better.

 

fittacular is more or less on the mark, with few exceptions. The devil is in the details, as with many complex multi-discipline endeavors.

dustinb.. if you have a specific set of mods and circumstances you would like to discuss, PM me and I would be happy to help if I have some time this evening.

There are very few people, fewer so on this forum in particular, qualified to discuss this topic.

Now I await the usual internet experts to show up with their inexplicable zeal (matched only by their lack of experience or knowledge) for going on tirades against anything greater than 87 in a Fit.

 

I don't think you'll have to worry about this at all with bolt-ons.

There are lots of threads on here debating the benifits of running higher octane fuel, take a look through them and pull your own conclusion.

Personally, i'd pay the extra few bucks for higher octane in any competitive driving event. It won't hurt, and hopefully it will help. Daily driving, just use 87 if you want, it won't hurt anything.

 

Thanks dsm, I don't build or even work on cars for a living, just like to tinker with cars as a hobby. Wanderer is 100% correct with his assertion. I put 93 octane because it's available and I can afford the extra cost. This is actually my first ride out of MANY that I can use 87 but I'm opting out of using it.

 

I also got use to filing up with 91 (highest available in CA) and now that i have a fit, i feel weird about anything different. I ran the idea with my pals and they brought up a good point which relates back to the first post. Our cars arent tuned to maximize higher octane. But this doesnt mean it will not show any benefits. I will also be honest and state i don't know if the motor has to work any harder to burn higher octane or what. But giving factory specs were designed to burn 87 safely i say its a good idea to stick with it (injectors,plugs, etc.).

Only question i would have is can using 87 hurt in the long run given the nature of the fuel. As in are the benefits of the cleaning agents and finer fuel that much more beneficial that my motor will last significantly longer. (k24 swap anyone )

 

If you connect a ScanGauge or UltraGauge to the OBD2 port and look at the timing, you'll notice that after startup, the ECU starts with very retarded timing, then gradually advances the timing more and more until it starts to detect knock, at which point it dials back a little bit. If you use high-octane fuels, the ECU will end up using more advanced timing.

The L15A with its high 10.4:1 compression ratio was designed to run on the most common fuel in Japan, which is around 91 or 93 octane equivalent, although you can get 95 over there if you want, if I understand correctly. Honda started exporting it to the States only after several years.

Just because 87 doesn't do permanent damage does not mean it's the absolute best choice for everyone's circumstances.