Good luck with that test!! It sounds like a nice trip.

 

Make sure the trip isn't in a direction that has winds that blow primarily in one direction. Out here, when I take trips west, my mileage is usually considerably worse than when I come back going east, because our winds blow from the west more than from other directions.

 

Thanks and very good point. The trip will be from So Cal to Vancouver, Canada.

 

That sounds like a really gorgeous trip. Have fun!

 

My dealer told me, in very emphatic terms, to only use regular gas, as anything else will actually screw up the on-board computer.

 

That is tough to swallow. Either the computer adjusts to the premium or it does not. Screw up the computer??? Not buying that one at all.

I use premium when I can find it without ethanol. That is the only grade I can find no eth, and usually only out in the boonies around the farming communities.

 

I can't say that I agree with your dealer's choice of words, but if he said that the 'computer couldn't take advantage of using premium,' he would appear to be right.

By the way for those who are following this thread, I have started my own un-scientific test of regular versus premium. I am using Shell regular 87 for the Regular gas and Shell V-Power 91 for the premium part. After 3 tanks of each (I am using the Fit's on-board computer for comparison purposes only and do not claim it as actual mileage). The three tanks of 87 resulted in 38.6 - 38.9. The three tanks of 91 resulted in 37.1 - 37.7. Rightly or wrongly why spend $.20 per gallon more for poorer mileage.

Until I take my long North/South trip this Summer, I will not make any mileage claims, but in the interim, I am going to save the coin and only use the 87.

Taffeta White
2010 Sport 5spd

 

Nice post about RON numbers. Here's my take from my previous tuning experience:

First off, #1. The ECM/ECU in the Fit CANNOT compensate for higher octane fuel. Period. USDM Fits are simply not programmed to do so. So anything higher than 87 octane is generally wasteful, and any perceived benefit is usually a placebo.

#2. There are lots of cars on the market that can adjust timing in both directions depending on octane, hence the caveat "for higher performance use 91+" in the owners manual.

#3. All vehicle ECU/ECMs have the ability to retard timing when knock is detected. Running lower octane than recommended can be accomplished but you run a higher risk pre-ignition and rely solely on the computer to detect it and compensate accordingly.

Some people will swear up and down higher octane worked wonders in their cars, but 99% of the time some underlying factor was the real contributer.

 

You need to read some of the other older threads that address this topic. It seems that all a person needs to see how much more the ignition will advance to benefit from the use of premium fuel is a Scan Gauge. There have been numerous people that have said pretty much the same things that you have and set out to prove it by monitoring the ignition timing using different grades of fuel. Quite a few of them found that they wanted to use premium fuel after having the results of their test with the Scan Gauge. All of them that thought the ECU wasn't capable of compensating with more advance with higher octane fuel before had to admit that there was considerable more timing advance with premium and also more low end torque and pulling power on hills. The ECU does more than just retard timing when ignition knock is detected, it also advances to the point of pre-ignition and backing off just enough to avoid it . This argument has been going on for years.

 

Assuming for a moment that the Fit does learn to advance its spark more with premium fuel, how does this equate to improved performance? Provide sources.

Also when you make statements about what you have observed, it would be helpful if you included the fact that you're running a supercharger.

 

TX Coyote, thank you for the insight. I was under the impression the Fit's ECU was not capable to do so, but thank you for the info.

Steve244, advanced spark means advanced/more complete burn before the exhaust cycle and equates to more energy (power) extracted from each combustion cycle. It's well documented. People have been playing with this since the advent of the combustion engine.

 

There are threads on this forum that have substantiated performance and fuel mileage gains from using higher octane fuel. You can read them with an open mind and learn or if you choose you can ignore the relevant information and focus on what you want to see to substantiate what you want to believe... My car being super charged has nothing to do with the way the stock ECU functions to maintain a higher amount of ignition advance when driving conditions and fuel octane will allow it to do so.

 

sigh... if it's well documented then provide a single reliable source.

advanced spark is necessitated by the slower burn of premium fuel. It does not equate to more energy extracted from each power cycle than regular fuel, if the engine is designed to run on regular fuel.

Premium fuel is necessitated by engine knock, resulting from higher compression (think 60's cars) and higher fuel/air ratios resulting from forced induction (turbos/superchargers).

Here's one source:
scientific american.

 

what, like this one?

 

What do you think the compression ratio of the Fit is?

 

10:1. And what is the impact of modern fuel injection?

 

E85 is not an octane rating, it's 85% Ethanol/15% Gasoline. You need a Flex Fuel vehicle to use E85, which the Fit is NOT.

Ocatane rating is a NOT a measure of quality, more a measure of performance. The book recommends 87 (in the U.S.) Probably wasting your money using anything higher. The only exception I'd make is at altitude. If "regular" is 85, I'd buy what ever grade (be it called "Mid" or "Premium") that would get be back to at least 87. Assuming I'd be back down from altitude on that tank of gas.

Using higher ocatane should do no harm to your car, only your wallet.

 

When you head to higher altitude, the ECM compensates to a point, but I'm wondering if anyone has any experience above 7,000 ft. I'll be heading to Colorado this April for 3 months and staying in the 7-8,000 ft range. Does anyone have any experience with Fit's at that altitude. My Tacoma doesn't seem to care, but it is about as sophisticated as a brick.

Taffeta White
2010 Sport 5 spd

 

Because of the lower oxygen due to the reduced air pressure you don't need as high octane. Regular gas sold in those regions is 85 instead of 87. Running 87 is not a problem (higher than needed doesn't hurt). Fuel mixture will resolve itself based on the MAP sensor (manifold absolute pressure). The end result will be slightly lower power (but better mileage!). Go climb a mountain!

Lived in Denver with a car bought in Miami. Lived in SLC too. You'll notice the difference but your car won't care.


Tacomas have fuel injection too.

 

I did my own test and can concur similar results. Mine did not get worse, it stayed the same. I went one full month on 87, another month on 91. Identical 7.2L/100 km (cdn model). I only drive the Fit to work. Consistently the same route to and from work for the entire month.

If you want more facts & myths read http://www.state.mn.us/mn/externalDo...ctaneFacts.pdf and save your money!

Stick with what the manual suggested. Mine says 87 and I'm going to live by it.