It will be interesting for people to do some experimenting with various octane gas in the GE's L15 to see if/when/under what conditions the computer starts to pull back timing (observed by a scan tool, not seat of the pants or speculation). It's not as simple as some make it out to be. Heat, elevation, and engine load all contribute to predetonation. In "normal" conditions, one would expect 87 octane to perform fine with little or no timing retard needed. But on a summer road trip in the Texas Hill Country with the car loaded up and the A/C on, higher octane may in fact offer a little extra timing advance and therefore power. I'll try to remember to hook up the ScanGauge sometime so I can monitor ignition timing, especially as the weather starts to heat up.

I'm not saying anyone should run higher octane. I'm running 87 and will continue to do so unless I find conditions that suggest some benefit of additional octane.

Increased altitude and lower temperatures both REDUCE the octane requirement of a vehicle. Definitely no reason to run 93 in those conditions.

Whether higher octane does make a difference or not varies from car to car. In another thread on this forum, someone established the fact that the Fit/Jazz L15A increases spark advance more when you use higher octane fuel. All other things being equal this would result in more power and better economy, but because higher octane fuel burns slower, it may be that this additional spark advance is negated by the slower burning fuel.

I have tried 91, 95 and 98 (Australian ratings, equivalent to 87, 91 and 93) and couldn't pick a difference. I haven't yet tried E10 ethanol blend.

I still think someone should dyno test a car running the various available fuel types to see what happens. I personally, will continue to use what the book specifies and pocket the difference

I've been using 87 and always will for the GE8.

My 99.5 VW passat with the audi v6 had a knock sensor, so it would do exactly this. The manual recomend 91+ octane for max power, but it could use as low as 87. I remember reading somewhere (too many years ago) that it was about 10-12% diff in hp and torque. This is all from memory so no promises on accuracy.

I'd be very surprised if the ECU in the Fit was designed to run at knock threshold, instead of running at a spark advance setting optimized for 87 octane, with hysterisis retarding/advancing if knock is detected. That said, I bought the car because it runs fine on 87, last thing I need to do is be back to running 89 or 91 in my commute car. I already have three other cars that won't run properly on anything less than 91 :)!

I've been using premium since I purchased the car in December and today for the first time, because of this thread, I used 87. I actually noticed a better response time. Is that odd?

No because the fuel is actually burning at the correct time without leaving any extra residue left behind. It's odd about the dynamics of octane but just use what the manual tells you and you should be ok.

I use 87 octane. Also like Tork said it burns slow and leaves carbon and on top of that you waste money. Just follow the manual and you'll be A OK!! :)

Just so everyone can read exactly what/how it's written...

Fuel Recommendation
Your vehicle is designed to operate
on unleaded gasoline with a pump
octane number of 87 or higher. Use of
a lower octane gasoline can cause a
persistent, heavy metallic rapping
noise that can lead to engine damage.

I guess we could now bicker that the manual doesn't recommend 87 per se, it recommends 87 as the minimum octane acceptable.

unless your ECU is tuned for fuel better than 87, there is ZERO reason to run it. you are going to be throwing your money away

No, that exemplifies what I and others have been trying to hammer into you guys' heads - using higher octane than recommended can DECREASE power and fuel economy.

There is a reason why I bought this car and it wasn't to unleash the performance prowess out of the dinky 1.5L Low output motor.

It was to save money in fuel costs. The last I checked, putting 89+ octane in the car contradicts what this car is all about.

If you want a more efficient motor, nothing beats regular maintenance ergo regular oil changes and tune up.

Its sucha simple motor and a simple car, why are we trying to complicate things? Thats what my S2000 is for :p

It takes more energy for your engine to burn the higher octane, can't burn all of it, which means less fuel economy, more carbon build up, etc. I mean I understand why gas stations call their higher octane fuels "premium" but it really doesn't do a car like ours any good. Use what the owners manual tells you and save your self a few dollars while you are at it. You wouldn't run 87 in your Corvette would you?

Before I cammed the Trans Am I strictly ran 91 because I'm that anal. It's such a pain in the ass to find a gas station that has 91 too.

if your car states that it is REQUIRED to use 91, use it. otherwise dont waste your money

Exactly what I was going to say. Please, these cars are designed to work with 87. Sure 89 would be fine but is not needed.

yes. even if it is recommended, it isnt REQUIRED

The Fit (stock) is designed to run on 87 octane. You are wasting your money if you use anything more. If your Fit is boosted, tuned with advanced timing, etc...by all means use higher octane. High octane fuel is used to slow the combustion process to reduce detenation on high compression/ boosted motors and maybe areas with very high temps. Sports cars such as Corvette, Cobras, GT-Rs, Ferraris, etc run high octane stock because they are either high compression or boosted.

If your engine is recommended to use a specific octane, I'd say it's pretty much required. The L15A has a 10.4:1 compression ratio, which is actually kind of amazing to use only 87 octane with. If you have a higher compression engine, OR have an engine with forced induction (thus, you have a greater pre-ignition pressure on the compression stroke), running an inappropriate octance can cause preignition (aka knocking).

AFAIK, knock sensors react to preignition to prevent future occurrences. You've already knocked when the knock sensor activates and retards your timing. Causing your car to limp because you're too cheap to spend another buck or two during fillup is not the wisest thing...

Just an interesting fact to add, In South Africa the minimum octane is 93 and Im almost always running on 95. I get the impression that the car runs smoother and with slightly better throttle response on 95 compared to 93. Will hopefully be getting a Scangauge soon so I can be a bit more insightful. Would be interesting to use octane boosters no?