Gas Octane

Hey Zack, tell Holly, Wad says HI!

 

Disturbing...

I think I'll try 91 next time.

 

Just to add to the mpg data pile, here's a couple of years' worth of mileage numbers from my truck. The dips are winter, the peaks are summer. The slight decline from one summer to the next was the result of changing tires. The overall average is 12.04 litres per 100km, with the last fill at 11.21. Those equal 19.6 miles per US gallon and 21.06 mpg respectively. This is 100% on ethanol-free premium.

 

As things get cooler (winter) air gets denser, which makes for more efficiencies. Refineries also switch from a summer blend to a winter blend at some point. I don't remember all the differences between the blends, but I'd imagine it would tweak mileage a little bit as well.

 

Not to mention pushing through snow for 4 months seeing how he lives in the centre of the universe

 

Creemore - makes sense. With the denser air your mpg will slightly drop....but more power. Summer increases your mpg but drops power. Love the 1/4mi in the winter hate it in the summer.

So those that use 91 or 93 w/ 10% E how much total increase do you see in mpg? Sorry I don't have the time to read 30 something pages.

 

It was previously stated that the engine adapts to the fuel in an EFI engine. It does this by monitoring ping. Lower octane ignites quicker, and will ping...so the ECU retards spark timing to eliminate pinging. Higher octanes are less likely to preignite or ping, so the ECU can advance the spark. This typically results in a crisper throttle response, which on turn gives bettter acceleration. You may also note better mpg, because spark advance will give better power, therefore at steady speed you use slightly less fuel compared to the same speed with a more retarded spark.

 

I kind of misspoke: Fuel economy gets worse for me in winter, better in summer. I've pretty much ruled out winter tires as a significant factor. It seems temperature related, and I've assumed that there's just a cold weather ECU map. I agree winter blends might be a big factor.

 

Wherever I am is the center of the universe, grasshopper

 

Actually, there's probably something to that. You'll see that I did slightly better last winter than the winter before. That lines up with the kind of winters we had (we actually spend most of our time at a farm north of the city). Last winter was warmer and there was less precip. The one before was endless.

 

I'm not sure about Toronto, but here in California they have "winter blend" gas which makes your mpg's go down as much as a couple of miles per gallon. Where I live we don't get snow so it's just the different blend of gas that makes a difference. Actually, I've gotten better mpg's with fuel from other states like Oregon, Nevada, Washington, Utah, Colorado, etc... California gas is supposed to be cleaner burning, but I seem to burn a lot more of it. I'm sure cold weather is also a factor, but once the car is warmed up it shouldn't make too much of a difference.

 

^^^ yes

Advancing the spark means the fuel has a longer burn time. Longer burn time means a more complete and controlled combustion of the fuel. When the fuel burns more completely you get more power and more MPG.

Those of us old enough to have actually owned a car where you could loosen a bolt and manually advance the tiimng know exactly how this works.

 

Advancing the timing has little to do with longer burn time and more to do with creating a higher combustion pressure. That's what increases power. By sparking the combustion before the piston gets to the top the gas explosion and expansion begins just before top and a higher cylinder pressure results with a stronger power stroke down.

 

Yep, higher octane = slower burn. High compression engines like this. Ethanol is what's killing our fuel, and our government wants to put more in! Even though it distroys thing in the engine compartment. It's just bullshit

 

Just came back from a 1177 mile trip towing 3000# going I used 91 coming back I used 87 the only difference was the amount of money in my pocket no more power and exactly the same mileage. The Ulta Gauge showed no gain in timing and pen and paper no difference in mileage.

 

Doesn't it take a few tanks for the engine to adjust ?

 

Adjust what? The closed loop ecu adjusts the fuel immediately.

 

This man speaks the truth! Modern vehicles (primarily OBD II+) have various sensors to provide feedback data to the ECU and adjust air/fuel mixture base that data for a "closed loop" operation.

 

+1

 

I towed 3000 lbs from Denver to San Francisco. Initially I was using 87, but since my truck seemed to be struggling a bit I started using 91. My mileage went from about 14 mpg with 87 to near 18 mpg using 91. My truck also seemed to have a lot more power using 91 which is what I was going for. The extra 4 mpg were a bonus.