91 or 93 Octane

[Prospero]

Ok, for those of us who have decided to heed the manufacturer's recommendation and use 91 Octane at least. I notice it says the car can run on 95 Octane Gas, 91 minimum.

So, for the mechanically illiterate amongst us, is there any advantage to using 93 Octane, where available, or is it overkill.

Note -- I'm not trying to reopen the debate of whether you need to use Regular or Premium gas. If you've decided that regular is ok, I think I sort of know where you'll come out on the 91 vs 93 octane question.

[sixcrows]

Originally Posted by Prospero

So, for the mechanically illiterate amongst us, is there any advantage to using 93 Octane, where available, or is it overkill.
.

I'm no wrench-head, so I can't answer with any kind of mechanical expertise.
I have put 24 tanks of gas in my smart.
16 have been 91 octane
5 have been 93 octane
2 have been 87 octane
1 has been 89 octane

I have not noticed ANY difference in the gas mileage regardless of the octane level of the gasoline. I can, however, state that my three highest mileage numbers were after 91 oct fill-ups (57 mpg, 51 mpg, 47 mpg).

The only difference I have noticed is that after filling up with 87 oct fuel, there seems to be a slight sluggishness in acceleration from a stop.

[NCC1701]

I've never used anything less than 91. Use 93 most of the time because that's what premium is, here. 91 or 93, I doubt the difference is really significant.

[fortow]

There might be a confusion between what is called "pump octane" and RON (Research Octane Number). Pump octane is what we refer to in North America and is computed as (RON + MON)/2 - and the significant mumber for that is 90. The numbers higher than that may be in reference to RON which is prevalent in Europe and elsewhere. Factory recommendations for MON (Motor Octane Number) are 85 and RON is 95.
There's no advantage to using octane higher than recommended.

You can get more information here - http://en.wikipedia.org/wiki/Octane_rating

[UAV-1]

Being a long-time Mercedes guy, one sort of gets used to using 93-octane as that's what MB recommends. So when I got my Smart, I simply continued because that’s what Smart recommends. (In my area, it’s either 93-octane or 89-octane.)

There’s a lot of emotion surrounding octane but from my experience, I get zero pinging, zero hesitation, slightly better MPG, and a bit smoother running engine by using 93-octane. And I have a ‘lead foot’. When I've been forced to lower octane, say because the premium pump is inoperable, I do sense a difference in performance - just a little - until I get the next tank-full of premium.

Yes, it’s a bit more per gallon. But considering the tank is only ~8 gallons, the cost difference – even with a bone-dry tank is only ~80 cents. I think I can afford a buck extra per bone-dry tank-full of fuel for a bit better perceived performance.

Cheers,
Jeff

[jimvw57]

I only used 89 octane once and got much lower mileage, like 35 compared to the 40 I normally get (so far) it does seem to run better with the higher octane. I want to try some different brands to see if it makes any difference. (only have 1200 miles on it so far)

[kannonvaggon]

There was a shortage of gas around Nashville last month whilst we were in that area doin touristy stuff. Many stations were out for several days and one could only get gas here and there which was a changing target. Big problems .

We could only get regular 87 oct fuel for a week. The car ran fine on this, but did show a definite decrease in engine power on the hills and also a definite increase in fuel consumption. No apparent pre-ignition or starting problems or anything like that though.

This is the only time we have run regular gas in the Smart and I don't plan on doing it again unless that's all that is available.

YMMV

[headless]

In Britain we have slightly higher Ron numbers, not overly sure about RON+MON or whatever, but Myself and all my smarty friends use the higher (superunleaded) fuel, the Shell Optimax is particularly good for the smart engine, it give improved performance and better gas mileage, and if I can't find a station that has super and have to use ordinary, the drop off in power is significant.
I think because the engines are small and revvy, they need all the help that they can get.
I don't put in a certain amount of fuel when I fill up, I put in £20 worth of fuel, and even though the super is a bit more expensive per litre, I can get further for my money, so why would you put in the lower powered cheaper fuel, go on give your car a chance and always use the best fuel available.
El.

[fmaxwell]

For most cars, a drop-off in power or mileage with a lower octane fuel is because the ECU is retarding the timing in response to a knock (ping) sensor on the engine. That's generally not a good thing. It's basically a safety system kicking in to protect the engine.

[gusfraga]

Originally Posted by sixcrows

I'm no wrench-head, so I can't answer with any I can, however, state that my three highest mileage numbers were after 91 oct fill-ups (57 mpg, 51 mpg, 47 mpg).

I can't get these mpg not even close.
Are you an hypermilinng guy?
Gus