87 vs 93: The Showdown.

[sx sonic]

all of my fill ups have been with 87 octane and now i was thinking of putting in a slightly higher octane like 91 or 93. would it be safe for me to do that. is there better performance as far as it cleaning the engines fuel system and different mpg rating.

- it will not harm your 1.4t (or the majority of semi modern engines) to run premium fuel.

- Octane is a "resistance to detonation rating", the higher the octane the more resistant the fuel is to detonation.

FYI detonation is when the fuel ignites before the spark plug fires. This is bad and can destroy the engine, cause a loss in power and mpg, and often produces an audible knocking noise (detonation is also known as knock).

Modern engines fight knock by temporarily retarding spark when knock is detected

- It has been established that the 1.4t ECM has a dual map feature. One map is purportedly optimized for premium fuel (slightly more power and mpg). IF knock is detected the ECM reverts to a safer tune (less optimized) that will prevent future knock encounters, and then fight knock on an on occurrence basis.

At each fill up the ECM reverts to the optimized tune.

So IF you knock on 87 oct you MAY notice slightly better performance and mpg.

-Fuel grade does not necessarily mean higher quality fuel, as I mentioned earlier octane is It's on thing seperate from cleaners, detergents, or ethanol. Premium MAY have more cleaners or detergents but that is entirely up to the parent fuel supplier.

- most of this has been covered numerous times in this threads and other octane related threads.

- Fill up a few tanks and note your average and see if it improves.

 

[Swordsmith]

Funny you mention that. Even with the small amount of data in the MPG comp. I can already see a difference in the results for 87 and 91. Don't think the 91 helps on the highway, it is during mix driving that requires acceleration.

Interesting, that does correspond to my gut feeling that 87 is the most economical fuel to use on long interstate drives; if we're mostly just putting in the bare minimum needed to maintain speed, and 87 does that job just as well as 93, but at a lower cost...

This could also account for the disparate results people are reporting, where some say the 93 is so much better mpg that it more than makes up for the added cost, where others are saying no, the mpg is the same but the cost is just higher for no reason.

The "best" way to measure mpg differences is to set your CC to operate at a specific speed, and to do a long back and forth stretch, so you can repeat the exact same thing with a different fuel, changing as few variables as possible. But this test wouldn't show the difference you are talking about at all, since it looks like if there is a difference in mpg between the two fuels it is during acceleration, which is precisely the sort of thing that test strategy is designed to eliminate.

Real world looks like our only hope of getting data. Hmm, how about this, what if we find someone who has a predictable city commute, and a buddy who will take their Sonic to the pump to fill up, and not tell the driver which fuel he is using at any given time. That should eliminate subconscious behavior modification, yeah?

 

[Stew]

Alright. I wasn't really buying the 'better mileage with 93 octane' being a big enough difference to really see an empirical improvement, but I'm ready to come over to the dark side.

I've always ran 87 octane since I drive 75% highway with the CC on, and some city driving and spirited driving thrown into the mix. I'm usually going for MPG more than anything else. I've been pretty consistent around 38.5 to 39 MPG calculated, and the DIC is actually usually within 0.5 MPG of this.

Well, I've put 92 octane, the highest in the greater Seattle area, for the last two tanks and on this tank the DIC is reporting 42.3 MPG with this tank being almost gone. The weather has been fairly consistent over the last several weeks and my driving doesn't vary significantly, so it would seem that there really is something to this.

 

[Crazzyboy]

without reading the other 200 or so posts I am pretty sure the dealer put in 87. Which I went with seeing as I didnt have a choice. Ran through the tank, think I got 29. But at the time Vegas was 115+ and I really did not feel comfortable with a turbo engine running 87 in this extreme heat. So the second tank I put in 91 and have continued to since. Mpg have been good at 33-35. Though I do not consider it comparable as the first tank or two in a brand new car is crap anyway.
One thing I will say the engine has gained a nice growl with 91. Was way too dam quiet on 87. Cant say I noticed any performance gains

 

[chivalryder]

My $0.02:

Here, in Ontario, you will always get ethanol in 87, up to 10%. Ethanol reduces gas mileage. Fact.

Though I haven't confirmed this yet, Shell 94 does not contain ethanol, thus better gas mileage.

HOWEVER.

87 in my area currently costs $1.35/L ($5.19/gal), and 94 is $1.55/L ($5.96/gal).

It usually costs me about $50 to put in a tank of 87. If I were to fill it up with 94, it would cost me another $7. Sure, that doesn't sound like much, but my budget is extremely tight and I put at least 4 tanks in her each month. When you have bills like I do, and you make as much as I do, $30/month is a LOT of money.

When I do fill her up with premium, then I do notice a big difference in how she drives. Maybe after my first raise, I'll start using premium regularly.

 

[sonichead94]

87 in my area currently costs $1.35/L ($5.19/gal), and 94 is $1.55/L ($5.96/gal).

It usually costs me about $50 to put in a tank of 87. If I were to fill it up with 94, it would cost me another $7. Sure, that doesn't sound like much, but my budget is extremely tight and I put at least 4 tanks in her each month. When you have bills like I do, and you make as much as I do, $30/month is a LOT of money.

Holy ****. Gas is not a joke down there huh. 30$ and im good for almost 2 weeks.

 

[chivalryder]

Holy ****. Gas is not a joke down there huh. 30$ and im good for almost 2 weeks.

Yeah. Now they're making talks about adding a carbon tax, which will supposedly increase the cost of gas my $0.07/L.

UGH!