Color me impressed. I was extremely skeptical at first, but it's hard to argue with an improvement this drastic.

I was switching between 87 and 89 octane for funsies, and driving mostly eco and occasionally aggressive, getting around 35 mpg (avg). I decided on a whim to try filling with 92, and was surprised to see that the average was 36/37 mpg, even with slightly more aggressive driving than previous.

92 is about 30 cents more than 87 right now, and if you consider the fact that I'm getting about 20 miles more per tank, that's almost a free improvement.

 

You went from 35 to 36/37 mpg. Assuming a 2mpg increase or 20 miles over a 10 gallon tank of gas, this saved you 0.57 gallons. At $3.50/gal regular this saved you $2.00. It cost you $3.00 more to fill with the $0.30 diff between regular and premium for 10 gallons. You "saved" -$1.00.

All this assumes your increased mileage was due to premium and not simply a better driving pattern over the tank. Using your own statements you went from "around 35mpg" to "36/37 mpg." I get that kind of variation from tank to tank running the same fuel and route. Color me unimpressed.

For a more meaningful comparison see Seldon's efforts over 1,500 miles. He got less MPG on premium. Assuming some margin of error it seems there is no benefit. Nothing close to this has been done by the church of premium fuel acolytes.

I leave you with this PSA:

 

I graduated with a degree in physics, so I have a strong grasp over what kind of differences are worth noting and what kind of differences are indistinguishable from noise.

I've run several tanks of 87/89 with a maximum of 35 mpg at the end of each tank, and a maximum of ~35.6 avg in economical driving (after enough miles to settle the post-fill meter.

My driving with 87/89 has been about a 7 or 8 on the spirited - eco scale (I coast to red lights/stops but accelerate a bit spirited with shifts at 3.2k RPM).

When I filled up with 92, I immediately did a few WOT for the ECU to detect timing, and proceeded to drive at about a 4-5 on the spirited - eco scale with a few more spirited accelerations than usual.

The MPG calculator has shown a maximum of 37 mpg, and has only dipped down to 35.7 mpg. In previous discussions on the subject, it has been pointed out that ScanGauge clearly shows the pulling of timing when using 87 octane. 10.4:1 is a pretty high compression ratio as NA engines go, and it's a pretty reasonable hypothesis that the knock sensor would cause the pulling of timing because of this.

I am in no way trying to say this is any sort of infallible scientific method here. However, my conclusions are reasonable based upon the information I have, though I withhold my definite conclusion until I get to the end of my tank.

 

Hey!
Let's start a thread about Synthetic vs. Dino-Oil!

Premium vs. Regular is a similar debate.

Everyone has their own subjective viewpoint, experience and opinion. My understanding is Honda and The Owners manual states a "minimum" Octane. They recommend you do not run "below" that octane.

But like many automotive debates? It's just up to the individual. IMO and in my subjective personal experience with my Fit? There are some tangible "differences" between running regular or Premium..IMO, I get less of that "Sewing Machine" sound with spirited acceleration. Like the OP, I also notice a slight MPG improvement.

Is this worth a consistent commitment to making my Fit a "Premium Only" vehicle?

As I've broken it in..and after a couple of Oil Changes either I've adjusted to the sound of the vehicle or the "sewing machine" sound has lessened...with either Premium or Regular...also, I've seen my MPG's improve across the board.

Right now...at near $4.00 a gallon or more? The immediate 30 cents or more savings per gallong of Regular is too much for me to abandon...even with a slight MPG gain.

I'm back to running regular...and I don't really feel I'm suffering from either a MPG perspective or overall automotive driving experience perspective.

I am one of those Crazy Bastards that do the worst....from time to time when I'm feeling like I might just be holding the winning lottery ticket? I might just randomly run a tank of premium...

Do I notice a difference? Yes....is it probably mostly psychosomatic? Yes...admittedly, the greatest benefit per 30-35 cents per gallon is probably all in my head.

Sometimes I do it anyway.

 

There's been many many discussions on fuel grade and fuel economy. A careful look through the ECO forums will show some and a search might reveal more. Tons of reading, little consensus.

I've been running premium fuel consistently since the end of winter. Does it effect MPG, I have found it does. Does my MPG vary, yes, slightly - many reasons for that. Bulk supply to the pump, local/daily environmental conditions, where I purchase, how I drive, where I drive, the list goes on.

What I have realized is that running premium does increase the basic engine response - butt dyno and observed timing advance. I can routinely drive in a more economical mode to get the same results I do running regular fuel.

For me it's worth the sight extra cost or savings - however, do we really want to split those hairs?

The only way to accurately measure the MPG is by consistent fill-ups and accurate mileage numbers. But really - MPG to the tenth is beyond knowing the average number your car gives you. I'm quite comfortable being within +- 2.

ItW - I think you're on to something.

 

tons of reading provides a wealth of evidence there is no benefit using premium fuel where it's not recommended or required.

If any of you would provide a single published article supporting your belief, whether from a scholarly journal or an enthusiast magazine it would carry some weight.

 

But the only thing I'm sure...published article or not....is that you aren't going to convince anyone. If you are convinced, by either experience or "scientificly supported article" that running premium is a waste? You will not be swayed by the subjective opinion of anyone. Conversely? If you've run Premium and "think" you are getting better performance and/or MPG? Then articles stating that it's a "proven" waste? Will mean nothing to that individual.

What you end up with? Is simply the "I'm Right".."No, I'm Right" never ending debate....

Run the octane that's right for you....and if you want to pay 30 cents more for it? That's okay with me...

 

Steve - there's really no 'point' to be made.

K_C_

 

Then why did the OP start the thread? Why are we responding?

 

There are plenty of articles that substantiate the benefits of using premium fuel.... The Fit has a compression ratio of 10.4:1 and that along with the ECU's ability to adjust to fuel with octane ratings way above 93 but not below 87 justifies using at least 91 octane as a safety measure to prevent engine damage from getting a tank of bad fuel that has a lower than stated octane rating than 87.CarNut's Garage - Does Your MINI Really Need Premium Fuel?

 

I already stated that people have plugged in ScanGuages and observed the pulling of timing when using 87 octane vs. 92 octane. I have also mentioned the compression ratio (10.4:1) which is on the high end for NA engines that are running 87. I will be able to give a better conclusion after this weekend, as I will be doing a good deal of highway driving.

 

Half a tank of gas probably isn't enough to prove a theory.

I put premium in once (gas station was out of regular) and noticed an increase in fuel economy...

Until I remembered- I didn't put the premium in my car, when the station was out of regular was when I was buying it for my lawn mower.

But I did notice a mileage increase and attributed it to something that it didn't turn out to be.

Why'd it go up? Change in driving? Change in weather? Car getting used to summer fuel? One less traffic jam? A couple of trips where I couldn't drive as fast as I normally do? Who knows?

My brother's a doctor. He said that even when they test growth hormone on small children- something not likely to suffer from a placebo effect- they still insist on double-blind studies.

I will say, though, that the Fit's engine having a high compression ratio may lead to being an exception to the 'premium fuel won't change anything' claims, especially if, as people have experienced here, the engine is changing timing with regular because of the knock sensor.

Does anybody know if the computer records knock sensor info so that a dealer could look at see if it's changing the engine?

Either way, though, the OP is saying that while his car got better mileage, it wasn't enough to offset the additional cost. "Almost a free improvement" really means "Not all the extra expense was wasted."

I've offered to buy an ultragauge and do a comparison test with two similar cars, but nobody's taken me up on the offer (I'm in the NY area).

 

It's not a theory, and Steve, as usual you are full of shit.

 

Fine, even if it's a fact, a half a tank still isn't enough to prove it. You've even said so yourself.

 

I run an UG, what did you have in mind as far as a test.

 

"Theory" is not interchangeable with "hypothesis."

I didn't say I proved a theory. I already said I'm withholding my final conclusion until I get back from my trip.

 

As usual, you have nothing to contribute other than insults.

 

Hmmm... water pill? sugar pill? or salt pill?

Chill guys, Happy 4th of July!!!

 

Please link one article that shows the benefits of using premium fuel where it's not recommended/required by the manufacturer.

From the article you linked (italics mine):

 

There is 10 degrees (+ or - a couple of degrees) more ignition advance to be had by using 93 instead of 87 octane fuel as seen on a Scan Gauge while at a steady cruising speed on a level road.... If you never wind up the engine at full throttle to the RPM that activates VTEC where all 16 valves are opening the ECU will not learn to advance and take advantage of the higher octane fuel so you will not experience any improvement in fuel mileage or power.... It is people that consistently drive at low RPM with a light foot that will do fine using regular fuel and actually get better fuel mileage with it... When I have driven like that using premium I get worse fuel mileage than I do when driving at higher RPM and occasionally at wide open throttle.