Regular v Premium Experiment

After joining TW I read a lot of back-and-forth on the whether octane has an effect on mpg but thought there were too many variables to cover over a short term trial (seasonal temperature, winter vs summer fuel, E10 vs pure gas).

So I thought it would be fun to use my Taco in a non-scientific trial over two years to see if there's a noticeable effect on mpg. Today marked the end of my little hobby/experiment and I've summarized everything below. Enjoy!

Conditions
* Only use E10 regardless of octane as it's been established E10 delivers ≈3-4% less fuel economy than straight gas. [source]
- This was easy as we only have E10 in MA/RI/CT.
* Each trial would run from Jan-Jan.
* My week long road trip in Aug '12 would be excluded so as to not skew results
- Resulted in removal of 4 fuel-ups
* Year 1 would be 87 octane, Year 2 would be 91+ octane
* Miles count toward Year 2 after the first 91+ fill-up.
* All fuel-ups are recorded in fuelly

Results
Year 1 (Octane 87 E10)
Span: Jan 08 2012 - Jan 13 2013 (29 fuel ups)
Miles: 9,413
Gallons: 472.515
MPG: 19.921

Year 2 (Octane 91+ E10)
Span: Jan 13 2013 - Jan 12 2014 (24 fuel ups)
Miles: 7,528
Gallons: 399.477
MPG: 18.844

Conclusion & Science-ish Observations
Octane didn't effect mpg.

Butt dyno confirmed there's a bit more giddy-up in the engine when running higher octanes. While this increased driver satisfaction, boosted male confidence and impressed womens, there was no significant effect on mpg from switching octanes when ethanol content remains unchanged. Going forward I'll be pumping 89/91 (preferably 91) as the engine response is more enjoyable imo...


EDIT: Want to add the following cause there's some question on why total mpg went down...

The summary is a little misleading. When I broke down the mpg's for summer/winter blends, the discrepancy was much smaller. I considered summer blend to be June 1-Sept 15.

87 Octane winter/summer mpg: 18.876/20.17
91 Octane winter/summer mpg: 18.355/19.67

In Year 1 I drove a higher % of total miles in the summer relative to Year 2 which slightly skewed the total.

 

I agree with the mileage figures but a butt dino is not particularly accurate. Personally I think your second comment is more accurate. Only thing I ever gained from using 91 was less money in my pocket.

 

Really? I thought there were a few stations that didn't run E10 for their 91...

 

if you find any in mass id buy my gas there.

 

Most "womens" are not impressed by the more sporty performance of your Tacoma when using higher octane fuel. Lower octane on the other hand is more impressive 'cause you got more resources (money) left. And man o man do they like resources!

 

My truck runs a lot quieter with 91 and so I switched and pay more. On 87 its loud and sounds rough.

This is just something I've experienced with my truck.

 

Yeah like Mr Salty said, my truck also sounds shitty with 87 and smoother/quieter with 91. Fuel from Mobil though always sounded shitty and rough. My taco seems to love Shell and '76 fuel. Don't know if there is even a difference from one brand to the next but this is my observation on how my Taco reacted.

 

This.

 

Sorry, only E10 in MA. Meant to say.....

I wish.

 

Good luck, tree huggers put the cock block on that. This state sucks.

 

^^ yup


It's nowhere to be found here.

 

Mr.Ziggynagy,

You said that octane didnt effect fuel consumption...But you show a gain of almost 6% using 87 octane.

Is that just not a significant difference in your opinion?

To me its a worthy difference.

 

Two stations within a few miles from my house.

 

You can find ethanol-free gas stations in Canada and the U.S. here:

http://pure-gas.org/

 

I'll throw this out also, going with close to the op's figures if you use 400 gals of 87 at around 3.40 vs using 400 gals at maybe 3.90 you're going to save only about $200 a year, which ends up being less than $4 per week difference. My point is for those who say they are saving money by getting 87, well yeah, but not that much. It's worth $200 a year for me to have a better running truck.

 

First I get "sir" @the gym, now I get "mr" @TW. Must be the beard.

The summary is a little misleading. When I broke down the mpg's for summer/winter blends, the discrepancy was much smaller. I considered summer blend to be June 1-Sept 15.

87 Octane winter/summer mpg: 18.876/20.17
91 Octane winter/summer mpg: 18.355/19.67

The variance is wider when summarized because the % of total miles driven in the summer in Year 1 was higher. So what appears as a 6% gain is actually ≈2% (which I didn't consider significant one way or the other).

 

Provided all things are kept equal, the lower octane fuel will make more power. This could be why you are seeing better fuel milage from the 87 octane. IMO, the only reason to run a higher octane fuel is if you have bumped up compression, are boosting the motor, or advanced the timing.

 

How do you figure? Here's the performance for the 1GR FE (easily found on the interweb)

87 Octane: Output is 236 hp @5200 rpm with 266 lb·ft of torque @4000 rpm
91 Octane: Output is 239 hp @5200 rpm with 278 lb·ft of torque @3700 rpm

 

"The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine."

I found the above definition using Google but I know it is true from automotive classes I've taken. A gallon of 87 octane gas has the same amount of energy as a gallon of 93 octane gas. Any improvement in performance is an illusion.

So unless your truck is knocking you are wasting money on a high octane gas.

 

I always use 87, but - I thought that with anti knock sensors, timing would be retarded to prevent knocking - so you wouldn't have obvious knocking, but may have less performance if the timing is being retarded? Or am I being retarded?