octane level?

[12V]

i've heard people say that their car can get better fuel mileage when they use "mid-grade" gas as opposed to regular.

I personally doubt that... but ...is that true?

[rage2]

Higher octane fuels burn slower, therefore create less power. You'll have more throttle input, therefore on a car designed for low octane fuel and is not suffering from pre-ignition on low octane fuel, moving up octane will have WORSE fuel economy.

[ACS-e36]

wtf?! so if i used the lowest octane gas are you saying ill get more power??!?!?! whats the point of having 94 octane for racing then??? or am i just confused.......

[HK2NR]

your car is designed for higher octane fuel

[dsm69]

octane rating is its resitance against nock

[2000impreza]

Originally posted by ACS-e36
wtf?! so if i used the lowest octane gas are you saying ill get more power??!?!?! whats the point of having 94 octane for racing then??? or am i just confused.......

more boost, more ignition timing, higher compression....

[rage2]

Originally posted by ACS-e36
wtf?! so if i used the lowest octane gas are you saying ill get more power??!?!?! whats the point of having 94 octane for racing then??? or am i just confused.......

Like I said, if your motor is DESIGNED for 87 octane, moving up octane levels will lower power output.

Higher octane fuel allows higher cylinder pressures, temps, etc before the fuel auto-ignites (detonation), so with higher octane fuel you can dial in more timing, run more boost, etc. without blowing stuff up.

[rage2]

Originally posted by 2000impreza
more boost, more ignition timing, higher compression....

Or what he said :D.

[ACS-e36]

ohh kay got it

[CanadaCivicSIR]

Does any one know the highest octane you can get from a gas station and which gas station has better gas, or a least which works best for your car!!!

I find Shell Optimax Gold is the best, but it seems not to last as long, as if I filled up at Esso and so.

[dsm69]

103+m+r octane unleaded aprox $2.30 litre. you can get higher but not sure its uleaded.

[RiceCake]

Didn't mission raceway have something like 127 Octane unleaded? :D

[rage2]

In Calgary, the highest octane "pump" gas is 92 octane, offered by Esso, Mohawk and Husky. Shell has 91 octane fuel. The Esso 92 is *slightly* better than Shell 91 (based on timing settings at the edge of detonation). Mohawk and Husky (same fuel) has the best octane properties, allowing me to run slightly more timing or boost as compared to Esso and Shell.

My testing on my cars, your mileage may vary :D.

[Maxt]

Yeah I would agree with that, about the design for lower octane fuel, but more so on cars that run traditional carbs and ignition systems. In this day of lean burn systems and computers that push ignition advance to the edge to meet cruise fuel economy targets, even engines designed to run on 87 octane fuel, will get better fuel economy with premium, as the engine will run leaner, and with more advance due to less knock sensed with the premium fuel. If you can run with 55 degrees advance on the highway , you will get far better fuel economy than being able to only run 45 degrees, you also have to factor in that the flame front will last longer on the power stroke with a slower burning fuel. Truth be known, as octane has decreased over the years, the cars have gotten far less thermally efficient, the old muscle cars were far more thermally efficient with 12.5:1 compression ratios than cars are today with 8:1 compression, if we could get cars today with EFI and those kinda compression ratios, life would be grand, however the oil companies make alot more money making 87 regular instead of 95 regular like the good ole days, and increased combustion pressures make more oxides of nitrogen which is smog..
What I don' like seeing is the gradual degredation of the fuels that we have seen in the last couple of years, mohawk and co. were all 93 octane, and the others were 92, but now mohawk etc is down to 92 and the others to 91, this is not good sign of things to come. Also I don't like the amount of alcohols in the fuel now, they have less thermal energy per mass unit, and they also require more fuel to air to reach a stoichiometric mixture, alcohol is 7:1 where as gasoline in its proper form is 14.7:1..
The bottom line is that they are chargin us more, selling us shittier gas, and they don't even clean the fuckin windows anymore...sums of a bitches....ok my rant is done...Maxt

[rage2]

Originally posted by Maxt
In this day of lean burn systems and computers that push ignition advance to the edge to meet cruise fuel economy targets, even engines designed to run on 87 octane fuel, will get better fuel economy with premium, as the engine will run leaner, and with more advance due to less knock sensed with the premium fuel. If you can run with 55 degrees advance on the highway , you will get far better fuel economy than being able to only run 45 degrees, you also have to factor in that the flame front will last longer on the power stroke with a slower burning fuel.

I'm going to have to disagree with you here. On "economy" motors, or motors designed to run 87 octane, they generally run a lower compression ratio, thus requiring less octane. Running higher octane will not increase the timing to create more power (improving economy slightly... see below) because there is a limit to how much timing you can run. Chances are the engine management is already dialed in to run the most timing (and most power available) on 87 octane fuel.

Timing can only be advanced so far... advancing too much will cause the burn to begin before the piston hits TDC, which is just as bad as detonation (power from burn while piston is still travelling up). Advancing timing gives more power for the amount of fuel used, so the driver "adjusts" at part throttle with less throttle input for a certain situation, therefore using less fuel. You're not magically going to get huge fuel economy benefits, the amount of power gained from timing advance isn't all too spectacular unless your timing #'s are heavily retarded (ie forced induction motors).

[Maxt]

What you say is true to a point, but if you have ever seen a "run of the mill" economy motor run with a diagnotistic interface connected, you can watch the computer continually cycle the advance up in search of higher values allowed on 87 octane gas, every wondered how OEM"s have been able to push the compression ratio's back over 8:1? Its becuase they can run on the edge of detonation thanks the the knock sensor something we could not do with carbs and conventional ingnitions...Maxt

[marek]

What do you guys think about the gas with those cleaning agents in it, such as what is offered at petro canada and such??

-mark

[Maxt]

I dunno about the "techtrol" BS, Petro Canada has the worst gas on the planet, hmm, no rx_7turbo2 has the worst gas on the planet..:)...
Petrocan gas has gotten progressivley worse over the years, I drive a truck with a 440 in it, now big bore v-8s with high compression do not take well to poor quality gas, I can't run that shit anymore, the truck pings with any kind of throttle input on that stuff.. Now I can go to Esso and buy there 91 and its ok..
Shell had a major issue with GM injectors and one of their fuel additives, in short they had to pay alot of peoples repair bills..
I wish we had Chevron 94 here, my car loved that stuff, and on my last trip to BC, I treated my GM savanna to tank of it, it ran like a different vehicle with the 94, I noticed it surged alot less on hills, and the mileage improved...Maxt

[red RX-7]

yah Chevron has some good gas.

i was in Golden B.C. and the 94 from chevron was .973

way to much money for gas. The gas price gose up the same speed as the amount of gas you get.

why cant gas be cheap?