I prefer to give it premium in the summer and regular in the winter. On hot days I can feel it pulling timing a tad with the regular fuel in the upper rpm so it gets premium then. Once temps stay under 50-60F, I go back to 87. Mileage is the same no matter what she drinks.

It really does depend on the car. The old civic had a little more low end with premium but its compression ratio (9.6:1) wasn't enough to support the slower burn. It developed carbon like you would not believe and it took months to get rid of it. Actually the old ford pickup was the same way... loved the good stuff, but it wouldn't start easily after a couple weeks because of the carbon buildup!

 

Sorry, I think this post may need minor correction or clarification.

A four cylinder, six cylinder, or fourteen cylinder engine at full throttle are all working equally as hard. Each have nearly a bar of air pressure pushed in and burn that air with fuel. Bigger engines just do more of this process at once. To work harder, the four cylinder would have to be boosted.

A wideband cannot tell the difference in stoich ratios for fuels. It only reads oxygen content in the exhaust. If it says 14.7:1, and you're burning stoich, that only means your sensor's reader is calibrated for gasoline. You could have ethenol burning stoich at 9.x:1 (whatever it is) and your wideband would read still read 14.7:1. That said, the stoich ratio of regular and premium is so close I doubt you could afford a meter accurate enough to tell the difference. And I hope you're not running full throttle at 14.2:1, that's quite lean and would push exhaust gas temps up. Old rule of thumb for old school hondas was to stay between 12.5:1 and 13.5:1 at WOT, between 14.5:1 and 16:1 for closed-loop.

For the GD3 folks that have pure speed-density systems (no MAF or LAF), it runs much like the older hondas: the engine computer reads manifold pressure and throttle position, compares with RPM in a preset table, runs the fuel value, reads the o2 sensor and fine-tunes, and repeats. This correction in stored as the short term or long term table adjustment and is called "closed-loop" operation. Once over about 80% throttle position or under about 3" Hg vacuum in the manifold, it just runs the table and says to heck with the o2 reading because the narrowband sensor can't read the rich condition that full throttle operation requires. No feedback, thus "open-loop." These tables got bigger when vtec came in because each valve profile had a table; the i-vtec stuff on the k-series is just nuts because with 50 degrees of play on the intake cam, plus the vtec, the amount of programming is just rediculous.

 

A wideband cannot tell the difference in stoich ratios for fuels. It only reads oxygen content in the exhaust. If it says 14.7:1, and you're burning stoich, that only means your sensor's reader is calibrated for gasoline. You could have ethenol burning stoich at 9.x:1 (whatever it is) and your wideband would read still read 14.7:1. That said, the stoich ratio of regular and premium is so close I doubt you could afford a meter accurate enough to tell the difference. And I hope you're not running full throttle at 14.2:1, that's quite lean and would push exhaust gas temps up. Old rule of thumb for old school hondas was to stay between 12.5:1 and 13.5:1 at WOT, between 14.5:1 and 16:1 for closed-loop.

I agree for the most part.
I only put that 14.2 fuel air because the car never went into open loop, there was about 6000 miles on car(Bp ultimate I think 7 percent ethanol). I also believe the new Honda Fit wont go richer than 13.4 -13.8 MBT. Richer mixtures are for max horsepower which the Fit is tuned for fuel mileage, and lower emissions. The Civic Si is another story.

February 2009 Total Performance Solutions Look at Jan,April,May too

Old Honda's were better and easier to tune too. You could swap parts and they made more horsepower with lower compression.

 

Scratch&Dent is doing some research that is showing information that ethanol in fuel gives leaner A/F ratio readings like you are talking about... He has a thread about using different percentages of ethanol in gasoline and it is getting very interesting.

 

How do you know it's there, and how do you know it's gone without tearing down the engine? (carbon buildup)

In two weeks I wouldn't expect an appreciable difference unless you are burning oil and your exhaust billows black smoke.

In two weeks I think the difference in starting ease using premium would be due to the higher ignition threshold of premium fuel. It probably took that long to completely purge the lower octane fuel.

Oh, and how does one "feel" timing being pulled?

I'm honestly curious. I only troll part time.

 

I don't know about carbon buildup, but I can speak to feeling timing retardation. Back when I was commuting to Atlanta and back, I regularly ran into situations where I would need to launch quickly (left turn across traffic, get into an opening, etc.). Especially in hot weather, the car would hesitate in a scary way. I mean, this wall of steel is coming at me at 50 MPH, and the car doesn't want to MOVE until it hits 2000 RPM. This problem was a little worse when I would use SP3 on my throttle controller.

Anyway, I didn't know this at the time, but it was because the computer was pulling timing. After I switched to 93 octane fuel, this problem went away. Once I learned about the timing, I used my ScanGauge to look at it, and sure enough that was what was causing the hesitation.

 

I think it says "87 or higher" for this reason, when your out on the road there are times where the station might be out of regular and you'd have to run mid-grade or premium. Premium isn't better, its got a higher knock rating, that's it. The ECU in the fit is calibrated to run on 87 and I'm sure its not going to pull more timing needing 89, 91 or 93, think about it. We're talking about a company that is best known for its engines.

IMO running 89 or 93 is possible but not neccesary in the Fit, you just wasting your money.

Premium isn't better unless you've got a forced induction car or hi-compression N/A car and it calls for it. Some "perf" cars, like the Contour SVT I had about 5 years ago said to run premium but if you use less than that, you'll not get the perf your accustom to. It certainly doesn't say in our owners manuel that if you run higher than 87 you'll get MORE perf, so why pay the extra .10 to 25 cents for mid or premium fuel. We're Honda owners, we're supposed to be smart, right

 

Yes your car will run on 87, but that dont mean premium wont give better mileage and have extra detergents to keep motor clean. If you are trying to get better mileage what rpm to you use lower than 3500rpm, thats where you use engine compression compared to higher that 3500 you use volumetric efficiency. As the engine goes up in rpm the the compression bleed off from 10.4(195 psi) to max. torque at 4800rpm (175psi) now add carbon and that raises. Your ecu will control it by adding more fuel and adjusting spark advance.

Claims of enhanced gasoline aren't untrue, just not particularly useful - NWautos

CARBON DEPOSITS: Cleaning Up What's Left Behind | Motor | Find Articles at BNET

Detonation and Pre-Ignition look under piston for hot spot deposits, I was talking about.

Force induction only raises the compression mainly at higher rpms when the the compression of the motor drops and the fast burn speeds of the higher volumetric efficiency's allow you to raise your compression safely.

 

I am a Honda owner and I am smart enough to spend my money on putting quality fuel in the tank instead of festooning my car with expensive knick knacks... If you have made your choice of what kind of fuel by using the different octane grades instead of reading what some other person that has no experience except with the cheap stuff, do you really know if there isn't a difference... There is a trend on FitFreak right now of people that have second hand knowledge (hearsay) telling people with first hand experience that they are the ones that aren't smart.... Have a nice day.

 

You don't need to waste money on premium to get adequate detergent. Just use Top Tier brands. they certify the detergent level in all their grades. www.toptiergas.com

 

uh, polaski up there is saying his use of premium in two other cars was the cause of carbon build up.

And forced induction works across the band on modern turbocharged/supercharged cars. (I say this from first hand experience.)

 

I am a Honda owner.

I am smart enough to put quality fuel in my car.

I'm also smart enough to not waste money on premium fuel.

See how easy that was?

 

Is it carbon build up or cleaning up the deposits of what left over from regular? I never had a problem with carbon build up with premium.

Forced injection engine has a lot lower compression and has a cam to bleed off pressure and raises compression at a higher rpm where it takes advantage of higher volumetric efficiency. I guess you never built a car with a 10.5 compression and a high duration cam with a lots of over lap to bleed of compression and ran premium in it because of knock.

I raced cars on oval tracks that would use 110 octane because its ethanol free and had a burn rate of 14.7 to 1 with a 9 to 1 compression. Now they use 98 octane unleaded. If you read the model t link its about the timing and fuel control and not compression to run higher octane. If your ecu cant adjust to premium your check engine light comes on. A big problem in the late 80,early 90s.

 

No you don't have to use premium unless you choose to.... Some people that have used premium have experienced better performance and fuel mileage and therefore made the choice to use premium... Some people that have chosen to use regular have also chosen to make negative comments about those that chose differently... Like I said in my first post you are the one that has to decide what you want to put in your fuel tank. If you think there is no difference buy the cheap stuff but make up your own mind and don't be critical of someone that chose one over the other based on first hand knowledge they gained from actually using both kinds for a long enough period to have an educated opinion based on practical use of the products in their Fit. Doing so is very sophomoric.

 

I wasn't bring critical of someone that choses one over the other. I was just stating that "You don't need to waste money on premium to get adequate detergent. Just use Top Tier brands. they certify the detergent level in all their grades." I made no comment about milage, performance or any other parameter, just detergent level.

 

I apologize because that wasn't directed at you... I can see why you interpreted it as being so...I did say "some people" twice and then got a bit carried away and was ranting.... Old people do that sometimes....

 

If it wasn't directed at me, why did you quote me?

 

We're not talking about Ford Model-Ts or race cars.

We're talking about a modern mass produced economy car designed to run on regular fuel.

Coyote there runs 6-10lbs of boost so he may need premium in his car. We don't

He was aiming at me and missed.

 

Why did you quote me Steve? I already know your out for me. Your opinion is not the only one out there. If a model T ford is to much for you and you cant understand that then how do you know that the ecu in the Honda Fit can run on premium? Take up any problems with Honda for putting 87 or higher and explain to them why your smarter than them.

 

Thanks Bullet.

What was your point? That Hondas can run on premium? No one is disputing this.

My point is there is no discernible difference between quality regular and premium fuels in an engine designed to run on regular. Honda doesn't recommend or require premium fuel for this car.

Please find a single reference stating otherwise, by Honda, or anyone in the industry.

I'll help: google: benefits of premium over regular fuel