Let me add to the entire vagueness....

You can go back within this thread and look at other posts I have made and you will see that I've filled mostly with regular...from top tier stations.

But I have an admission.

The last 2 tanks, just for kicks...since my 1st Oil Change...I decided to fill with Supreme...(93 Octane)....really just a whim no real reason.

Now maybe it's just in my head...but I have to admit The Fit seems to be running a lot quieter and smoother. Especially at idle and early acceleration...which seems stronger.

Plus my gas mileage according to the monitor is about 2 gallons higher than I have been averaging with regular.

Of course 1 1/2 tanks isn't conclusive...and a lot of this is simply immediate observation. But I might have to change my recommendation if this continues. I am going to continue to experiment. Think I'll fill once more with supreme and monitor, then fill with regular....see if my mileage drops and/or I notice more "noise"...

I really believed or leaned towards the idea that with The Fit there was no or little advantage to higher octane...but I have to admit..at least for a tank and 1/2...there might be....

Of course this also could be attributed to my recent Oil Change as well....so I'll continue to experiment.

 

That is high-compression for sure, but don't you think that Honda would've said to run higher octane than 87 to run this engine safely? Surely they wouldn't want hundreds of thousands of motorists driving their cars around with 87 octane risking pre-ignition, thus chance of blowing a head gasket

I will try this "test" and report back here!

 

In general I think this is true. However I think Honda's engineers were clever enough to work out higher compression with engine designs that negate this. Honda does not require or even recommend anything but regular gas for their cars (the only two exceptions are a recommendation for premium when towing over 3,500 lbs in a Pilot or Ridgeline).

The question remains; does using premium improve performance? Other than anecdotal, subjective evidence there is nothing to suggest this.

If someone came up with a single quote from a respected publication that there is any advantage to using premium fuel in a car where it's not recommended, I'd take notice. This hasn't happened.

Here's the conclusion Car and Driver came to almost 10 years ago:

 

A couple of dyno runs from a reputable shop would be interesting. I think they're around $60 each. An automatic transmission has problems showing accurate HP/Torque on a dyno so it would have to be a MT.

I don't think it's worth $120 to find out (and I don't have a MT anyway). Besides you'd get strange looks taking in an unmodified Fit.

 

I was wondering your car is manual or automatic? The only time I get high gas mileage is on the freeway or driving down hill. Around town I am getting around 31 mpg. I am at 4500 miles now. I have an automatic Honda Fit Sport.

 

Seeing that a dyno is a tool, I don't think it would look strange at all

 

@fitchet:

A number of Fit owners have reported that mileage goes up after the first oil change (I mean very first in the car's life), so that may be what's happening. It's related to breaking in the engine, as well as--possibly--the manganese in the oil from the factory.

Please keep us updated!

 

Yeah the first oil change is the motor breaking in for sure. I've added 0w30 Mobil 1 when I was back home 2 weekends ago and I reported 41.3 mpg on the way back to Chicago. Previously I netted 42.8 mpg with the stock tires/wheels and intake. Now I'm not going to say the mods affected my mileage other than the fact that the tire/wheel package weighs about 1.75 lbs more. Funny thing is this though, I got 39 mpg going back to Detroit and that bested my best by 1 mpg, same route and speed.

I like how we're able to talk numbers with our cars, not HP and TQ but rather MPG and not MPH

 

This is the only forum I've been on that people put fuel economy in their sigs in a non-sarcastic fashion


I mostly stopped in to comment after reading some of the back and forth on page 4, so here goes:

There seems to be alot of confusion on what cars can or cannot do as far as recognizing or adjusting for different fuels. There also appears to be just as much confusion about the implications of these different fuels and what actually happens in practice.

One gentleman suggested that because 93 runs leaner they run more timing. That is sort of on the right track, but it's more that the ECM registers over time the combustion events are becoming slower and cooler, and it changes what part of the interpolated MinOct/MaxOct Fuel and Timing tables are to be used.

One of the common ways to determine where in the tables the car should operate is Knock, if theres no knock that means the engine can try more aggresive timing and fueling routines, in most cases above 2krpm that involves as much as 30* advance and running 14.7-15.4:1AFRs in low load acceleration, decel or cruise conditions. At very high load and low rpm, the engine on the same grade of fuel has to sometimes retard timing and richen the mixture to achieve MBT.

When you combine knock, narrowband o2, IATs, IDCs, MAP sensors and in some cases alcohol sniffers in the tank or charge piping, the computer can make a pretty good stab at the quality of fuel.

Then the ECM will assign it an often arbitrary "Octane" value, in many ECMs it is between 0-255.

0 would put you exclusively on the MinOct timing and fuel maps, where 255 would place you in the MaxOct regions. Everything else in between is then at the computers discretion based on immediate conditions.

Values of zero are near impossible to reach in the US, unless you are a complete fucking idiot and cannot hear pre-det under boost for like 2-3 minutes of abuse... even then if you park shut down and restart you will be at 255 again and be on your merry moronic way!

So depending on the range over which the computer is allowed to adjust fuel trims and octane values you may be able to run a whole slew of fuels.

What I am getting at is, though I would be more interested in what the OE calibrators have to say, random guy at the dealership or random honda tech may be right when he says you would see little to no gain for using better quality fuels, but only because the computer cannot recognize or perform what it hasn't been programmed for.

So if the most aggressive tune they dyno'd in was for 91, that's the best performance you'll see. Though on 93 the car may run cleaner, smoother and more consistently as a fouled, stale or watered down batch of 93 still has a better proportion of octane to less stable heptane.

To the person who pointed out our high static compression for our L15As, I couldn't agree more. An indexed and tighter gapped (slightly colder than stock heat range) spark plug, good fuel and cold air are key.

I personally run 91 where possible because they mix in 10% ethanol (114 oct. and it brings it's own oxygen to the party!) around here, so the quality of gas that they mix with ethanol to come up with 87 oct [(RON+MON)/2] figure is probably just a tad better than straight donkey piss. This does change your AFRs though, from ~14.7:1 to ~14.1:1, consequently raising your IDCs.

But a cleaner combustion chamber and wider margin of safety for high rpm knock is worth the extra buck or two at the end of a tank, you cheap skates.

I also have a couple turbos to feed, so I am used to paying premium when theres no 93 or E70/85/98 but there is nearby air port with 100LL, or a race shop with something like Q16 available. Even though one is 8.1:1CR it still has to swallow 35+ psi boost. Better fuel harms no one but your wallet, and if cash is so tight that ~$2-3/tank is gonna break you perhaps you should get an echo, metro or prius

 

What are the turbo's attached to that you feed

 

Of the one I have pictures loaded to my imageshack:



Sorry for the gigantor picture..

This is a 65lb/min Borg Warner diesel turbo on a 2.0l gasser. The only thing not in the pic at the moment is the meth tank and computer, but you can see the plug and pigtail peaking out right above the intake air filter. I am using FIC BlueMax 1450cc injectors and a 675cc alky nozzle attached under the throttle body elbow.

The other car has a greddy clipped TDO5H 18G with 680's.

The truck which was sold is a compound turbo'd 12v Cummins with a Holset HX40 being facef*cked by an HT60 using propane injection.

I know I need to re-tuck the wires, zip ties, and stuff but I just changed the charge piping and a bunch of gaskets so everything was apart, so I had to do a boost leak test to make sure I wasn't going to pop any hoses or couplers. This pic was taken on saturday morning. It changed my VE table significantly so I have to re-calibrate everything, again. lol (yes those are cruise control throttle cables over the intake manifold)

Speed Density is a cruel mistress when you change something that effects pumping losses.

 

i get better gas miles with 93

 

This is the turbo I intend to use on the Fit when my warranty expires in 2011:

 

For comparison purposes:


BorgWarner S259ET (~65lb/min) on the left, MHI 14B (~34lb/min) on the right.

 

Holy BIG turbo and BIG picture

 

Sorry, I can't seem to get it smaller and stay in proper proportion

The scary bit is, that "big" turbo is still considered only medium framed! Think GT3582R..

It's actually third from the bottom of the BorgWarner size spectrum, being only an S200 family turbo, though it is the biggest in the family with a 59mm compressor inducer. There is still the S300-S500's families to consider.

The 90lb/min divided-T4 Holset HX52/55 that is going on my current motor build is close to BW S480 or Garrett GT40/42R territory!

Though that will be finished probably just as I am starting surgery on the Fit next spring/summer.

 

I appreciate your well written post, but this assumes that premium burns cleaner, and that regular will damage an engine designed (and tuned) for regular at high RPMs. Please cite evidence supporting either (there is plenty negating it). Also hyperbole such as "donkypiss" is not meaningful. Donkypiss might be very well suited to Fits (or Echos or Priussss).

There is no evidence to support that Fits "learn" up to a higher level of performance. I think this behavior is reserved for forced induction tunes (and I may be stating the obvious, but your post obscures this fact). Outside of the Honda engineering department that programmed them (and they aren't talking) no one knows. Logically there is no reason to suspect there is untapped energy from the fuel burned in our fits that is available with a higher octane, as long as the timing is correct for the octane used. There is a wealth of evidence that cars designed for regular don't perform significantly better (or worse) on premium fuel.

I do have a GM LNF sitting in the garage and am vaguely familiar with the necessity of premium fuel in cars designed for it, aftermarket tunes, and their ability to learn up to a higher level of performance.

And since we're having show and tell tonight:

 

Since temperatures have been in the 70s for a few days, I have seen ignition timing as high as 43 degrees at 45 to 55 mph and that is with boost...... I can not understand why a person has the audacity to expect someone to spend $120 on dyno runs to prove to him what he can see for himself by spending 2 extra dollars at the gas pump twice..

 

And attaching a scan guage to see such results.

 

: You can feel the results without the scan gauge but it does show you why the higher octane fuel is making more power, torque and fuel mileage figures.... It's a great little tool. I was stupid to have waited so long to get one