87 vs 93: The Showdown.

[AxelRipper]

So I decided to test out the differences between 87 and 93 octane fuels in my car. These are the 2nd and 3rd tanks of fuel to be put through my car, including the full tank it had when I picked it up at the dealer. I drive a good deal of highway all at 75, with a bit of city tossed in, probably 80/20. This is southeast Michigan so the highways are anything but flat or smooth.

First tank on 87: 30.2 MPG.

First tank on 93: 32.6 MPG.

Doing the math on this, if you take the amount it costs per gallon.

87: $3.38

93: $3.58

And then divide by the MPG to get $/mile:

87: $0.11192

93: $0.10982

So if you figure 300 miles between fill ups (gives abt 100 miles reserve) you get the cost of:

87: $33.576

93: $32.946

Yes, that is a difference of $0.63 per hundred miles! And this was 93 from Sam's Club!

I think my math is right on this, might have an error somewhere, but I would say this combined with the fact that you're getting more power from the 93 would mean that it is worth it to run 93. Yes, there are more variables than this and I may check it again sometime in the future, but still its pretty good.

This test was done on a 1.4 LT Hatch.

 

[Sonic]

I don't know what the dealership put in my car before I picked it up, but I plan on running nothing but 92/93 from now on.

 

[doreo]

i dont know a whole lot about gas and **** but i cant argue that my car has picked up about 3-5 mpg after my aggressive as **** tune requireing 93 octane.

 

[Sonic Boomer]

Thanks for doing this!
Since you weren't sure, I double checked your calculations, and another way to look at it is:
You are paying 5.92% more for 93 gas and getting a 7.95% increase in gas mileage. Thus you benefit 2.03% by using 93.
2.03% of $3.38 = $.0686 per gallon and for 300 miles you use 9.20 gallons which works out to $0.63 per 300 miles.

It looks like if using 93 gives better performance, it's free!

If you plan to do a Trifecta Tune (like me ) one of the "cons" is that you are paying more for the 93 required to get the benefit of the tune. Your data would suggest that this really won't cost any extra.
It is not good science to assume a tuned Sonic would yield similar data, but I like the results so I'm goin' with it!

 

[AxelRipper]

Yeah, I'm not planning to tune this until either the warranty runs out/car is paid off or theres a GM Performance Stage kit for it. I value warranties too much.

 

[wingman]

Y'all are lucky, best around here is 91, and thats roughly $3.75/gal.

 

[doreo]

you can have them tune for 87 if you like it just wont be as aggressive with timing as with 93 but i tell you on the 1.8 at least the tcm tune its self made me so happy that when the pcm tuned i felt like i got 2x the tune for the price of one lol. and it may be bad science for my estimates but i know at the end of month 1 for gas i payed more without the tune then i did the end of this month and i got more driving done by a few hundred miles so im loving it lol. though i must say i dont think the 93 did a whole lot before the tune but i wasn't in a position to really judge mpg just power and that was power felt not monitored via dyno/guages

 

[Gimpster]

FWIW also in my testing, and my iPhone app I keep track of things can back this up, 91+ has also netted me better MPG on highway driving. In the city though it seems to be a wash, but I've not done enough city to really back that up. I'm getting to the point with putting mods on the car running 87 doesnt make any sense, and I have to run 91+ in my Mustang anyway so I'm used to it. I also buy most of my fuel on my BP card which gives me rewards for 91+ hehe.

You can feel the difference between 87/91+ if you get in the wind in this car too.

 

[RockTheShazbot]

Finally did my first fill up today. Average was 28.5 in all city driving. After a reset, got it up to 32 right now. Still breaking in the engine before i take it on the tollway

 

[AndrewGS]

I made my sixth fill-up with 93. I'm not sure if it's just my brain wanting to feel more power, but the car felt like it gained something. We'll see if the mileage changes in my mostly city/suburb driving, but even if it doesn't, what's $2 per fill up? lol

 

[Eric Smit]

Don't know why it's never been mentioned, but at least where I'm at, the premium fuel has 0 ethanol while the regular is 5-15 (seasonal). That could easily be the mpg gain.

 

[Sonic]

No difference observed yet.

 

[laborsmith]

No difference between 87 and 93? Could be, as the reasons to use 93 in a forced induction motor are not related to improving miles per gallon.

But we know ethanol reduces mpg, although E10 would not reduce it as much as E85, nevertheless any amount of ethanol has an adverse effect on mpg.

Laborsmith

 

[oldertech]

Just noting here that the Chevy Volt specifies premium for the 1.4l engine that runs the extended range generator. I had read that GM said it was more efficient that way.

Highest octane premium I see in our area is 91 octane. I have to use that in my antique MG.

 

[Sonic Boomer]

Just noting here that the Chevy Volt specifies premium for the 1.4l engine that runs the extended range generator. I had read that GM said it was more efficient that way.

Highest octane premium I see in our area is 91 octane. I have to use that in my antique MG.

I have read somewhere that premium gas is slower to go "stale" and since the gas in the Volt could be stagnant for a long time if you have a short daily commute it made sense to use premium.

 

[Sonic]

I have read somewhere that premium gas is slower to go "stale" and since the gas in the Volt could be stagnant for a long time if you have a short daily commute it made sense to use premium.

That is the main reason it requires premium.

 

[Mike-NH]

I can't break it down by city versus highway, but when I've tested my 1.8 w/auto on 87 vs 93, I average around 2-3mpg better on premium per tank, everyday mixed driving. That works out to 20-30 miles per fill up, which is around 10 gallons, so more or less that's fairly close to a wash if you get a decent price for the 93.

The key is that I have to shop around because the place that sells the cheapest 87 is NOT the place that sells the cheapest 93. While some stations charge 20 cents per gallon more than regular - 10 cents per grade up - as many of us are used to, others here charge 25 cents, and some 30-40 cents per gallon more. In my neighborhood, Hess charges 3.37 at the moment, while BP charges 3.56, and Mobil 3.43 - while all their regular gas prices are within 2 cents of each other.

 

[RichieRocket]

No difference between 87 and 93? Could be, as the reasons to use 93 in a forced induction motor are not related to improving miles per gallon.

Laborsmith, per the discussions, there are two seperate issues here.
As you say, 93 allows higher boost on your forced induction motor without pre-ignition or detonation, producing more power when you are "on-boost".

BUT the subject here is mpg, so steady cruising on the highway, it is "off-boost". The engine computer can advance the ignition timing until it detects knock, then back off a bit. With 93, more advance is possible, producing more torque for a given amont of fuel, more efficiency, better mpg. So it is related...

I wonder if the variable valve timing may be adjusted to increase the 'effective' compression ratio by varying the open/close times of the intake and exhaust valves seperately? That could increase efficiency also.

I can't wait to get my Ultragage and track the ignition advance for different fuels and see if there is a noticable difference...

 

[laborsmith]

Looking forward to learning what the Ultragage tells you. Last time I looked they were still on backorder, is there any news on that front?

I agree that there should be some difference in mpg but I would be surprised if the difference does more than make up the difference price per gallon. Since I always use premium for forced induction engines, I have nothing to compare so will depend on your findings.

Laborsmith

 

[dvn]

Ultragauge on backorder until 1/6/12 now.