I would venture to say your 'spirited' driving has a bit to do with with the timing curve as well. And others should note you do sit at idle a lot by using your Fit as a delivery vehicle. That is a good representation of a 'commercial' use profile. Not many others use their ride as you do.

 

Any ecu with knock sensors does exactly as you state. A question is, over what time period does the cycle between retarded timing and maximum best torque timing (more advanced) occur?

My opinion is Honda (or any car manufacturer) would not have designed a normally aspirated engine to retard timing over several hundred miles until resuming a more efficient value. I think this cycle would be measured in at most seconds, and probably milliseconds as a function of engine revolutions.

I think the stories about ECUs learning back up to a higher performing level over a longer period of time (several key cycles) are from factory forced induction cars, or aftermarket ECUs designed for forced induction. The likelihood of forced induction cars incurring knock is much higher making it important to protect these cars from frequent knock. I know this to be the case on my GM LNF turbo. I use only premium in this car; it's required after upgrading to a more aggressive tune. Maximum experienced boost went from about 15PSI to 22PSI (with the absolute max being around 25PSI according to specs) with the upgrade.

See, I'm not a complete regular fuel bigot; only where it's not recommended/required.

 

I think I will try pumping premium

 

Normally when you feel the difference with premium it's in low rpm, high load situations where the computer will be pulling timing. You know, the situations where an old Ford 302 or something like that would try to ping on you. The motor will feel torquier because the engine can lose efficiency with regular octane fuel at those lower rpm.

As this is the situation where hypermilers love to pulse, it's possible to realize mileage gains there as long as you drive at low rpm.

Also noticing a very odd situation with my fit at 66 mph that I need to replicate more where after a few minutes on cruise it pushes ignition like nuts and will do 50+ mpg without any effort from the driver (tank average was 47.9). This could be made possible by premium in the tank (which I don't normally run) as well as my valves being set on the loose side of the spec allowing them to run cool.

The car shouldn't get mileage like that when it's turning at 3140 rpm but somehow it is (and did on a cross state trip the other day without varying). I mean holy smokes the needle didn't get down to 1/2 tank until just under 250 miles and I didn't even top off- my normal half tank mileage is 160 or so. Need more experimentation...

 

I think you've found the Fit's 'sweet spot'.

 

I use premium as well. I just made a 325 miles trip to Ocean City. I used 7.57 gallons. MPG is 42.92601 (actual) vs 45.8 (display). The MPG dropped dramastically from 52 mpg to 46 mpg when I struck on the Bay bridge for 30 minutes. 18x7.5 wheels.

I used to make 496 miles with one tank of gas. Stock tires/wheels.

I cannot compare with regular since I use premium from the beginning.

 

As intuited by KC, there is not a significant difference in MPG between using regular and premium over the period of time you were keeping records. Calculations

However since the time frames for observations of regular vs premium are not over the same seasons, I think this is inconclusive. Please give us more data in January 2012. Until then, carry on with your butt dynos.

You paid an average of $4.23/gal gas for premium and only $2.94 for regular? How times change...

With the same mpg and a assuming $0.30 difference/gallon between premium and regular you paid $110 more using premium fuel than if you'd bought regular over the last six months.

 

$110 That's a lot of money.... It is almost as much as I spend on chewing gum or about half what a person will spend that purchases a cold drink from a vending machine daily.

 

True. That's a big advantage driving an economy car, you can indulge yourself buying it treats. Me, I'd rather have the gum or the drink.

 

I stand corrected... sort of.

Anything more recent than 10 years ago?

While it is true that the time interval/seasons don't match up. You can draw some conclusions if you get the temperature range in. Weather is cyclical... so as it gets colder in one season, it gets warmer in another. If we limit it to say September or October to December, I'm sure there's a similar weather conditions in say, February or March to May.

But... as I mentioned in passing, I did change my springs and wheels/tires. So, any comparison will not only compare mpg of regular vs premium, but automatically include wheel/tire weight/rolling resistance comparison. Of course, on top of that is my inconsistent driving behavior.

To get more accurate information, I'd also need to do another year, using premium but switch back to older tires (not going to happen, since one tire has a hole and they suck in general).

So ultimately, for my change... it's worth it (since going up to 205 tires is supposed drop mpg).

As for the $110... its a lot for some, not as much for others bit. And for me... it's enough to enjoy some spirited driving.


I don't chew gum as much as I used to, though I do like to chew gum. And I buy my soda from Costco. I save on the Pepsi, to spend on the car.

 

Nope. This is the only dyno test comparing regular with premium I could find. At least it was during the age of electronic fuel injection and spark control.

Looking at two, 6-week periods, having similar temps (a swag, what do you think?) 10/4/2010-11/18/2010 (regular fuel) and 02/6/2011-03/16/2011 (premium) you got:

regular 31.00 MPG
premium 29.83 MPG

When did you change the wheels/tires?

edit:

Expanding the two periods to 10/4/2010-1/10/2011 (regular) and 1/23/2011 to 3/16/2011 (I left out the first two weeks on premium to allow for the Fit ECUs higher learning function) you got
regular 29.93
Premium 29.86

This is fun.

 

A CAR & Driver article that states that at that time not all cars that were made to be run on regular were capable of advancing the intake timing to take advantage of the benefits of premium fuel. Page 132 of my owners manual states. "Your vehicle is designed to run on unleaded gasoline with a pump octane number of 87 or higher".... There have been numerous people that own Fits or Jazz automobiles on forums all over the world that have said that the the octane rating of the fuel they use the better their cars run... There are numerous people that are automobile enthusiast that are here using this forum to discuss their experiences with their cars and have explained to you that the ECU is capable of advancing ignition timing to as high as 50 degrees before top dead center... Your shit is weak and flaky man, you need to take your silly game somewhere else I'm not jacking around with you anymore and I strongly advise anyone and everyone to just put you on their ignore list and stop being conned and manipulated.

 

Pretty close! I changed my wheel/tires right about the end of that premium period, 15th.

I was thinking about this as I was in the shower... I thought about using February too, but there's a flaw in that February time period.... there was plenty of snow on the ground (slipNslide!). But none in Oct/Nov.. or even Dec. So, unfortunately, conditions aren't similar enough (not to mention it was much colder in general this year anyway).

 

And yet we have no advantage in terms of MPG. And yes please, don't jack around with me.

 

That helps.

Using 10/04/2010-01/10/2011 for regular and 03/10/2011-05/02/2011 for premium you got:

Regular 29.93
Premium 31.24

A 1.3MPG advantage (4%) using premium.

 

Steve - do you really have to push things to the limit?? How about this, You've made your point -now let it go. Move on. Find something else to tackle and drag to the ground. I've been watching and many members have tried to explain in many different threads and you've managed to test their limits - and you seem to take joy in it????

 

I'm sorry. You're right.

 

What do you do for a living???

 

IT. Yield management mostly. You?

 

Then you should understand that a positive influence does not come at the result of antagonizing behavior. I'm a retired architect.