I need to settle an argument with someone in real life. I am looking for real world results from people who have tried 87 and 91 in the same G with the same driving style.

Please only give your numbers because these 87 vs. 91 threads often seem to turn ugly. Thanks.

 

unfortunately i don't have any numbers, but i can say that the car doesn't run nearly as well (felt, sounded and ran like a 4 banger) on 87, and 91 seems to go further between fill ups.

 

Basically that is what I am trying to prove. Even if the car can run fine by retarding the timing enough I am trying to prove its more financially advantageous to use 91.

i.e 93 is 4.11 and 87 is 3.91 here. That is a 4.8 % difference.

I average about 21 MPG mixed driving. If it went down to 20, that is 5% meaning it is cheaper to use higher octane even though it cost more per gallon.

 

I'd sure like to see some unbiased numbers on this one. Subscribing.

 

Over the winter I tested this idea. After my wife complained about me "needing" premium for the car. For 2 months I ran 87 and next 2 months I ran 93. I went through 5 tanks of gas each month. I feel the numbers speak for themself. On 87, I averaged approx. 320 miles to a tank=19MPG. On 93, i averaged approx. 360 miles a tank=21MPG.
This one done on mostly city driving and what I'd call semi-sprited at times.

 

Recently buying this I have run 4 tanks through. I have run 2 of premium (93 octane) and 2 of 89 octane (forgot the name). The 93 got better gas mileage over all then the 89 but only a mpg or 2 better here is what i got...
2004 G35 sedan hand calculated...
All highway with 93~ 25.37mpg
All highway with 89~ 23.68mpg
All city with 93~ 17.23 mpg
All city with 89~ 16.03 mpg

Now this is not really 100% accurate as I can not recreate the same weather and traffic situations but it gives you an idea.

 

Wow this is very interesting. Thanks for the responses and for the OP for creating this thread. Subscribing...

 

Judging by the results so far, it looks like it is cheaper to use 93 than 87.

 

on 93 ive averaged 24 mpg
on 91 ive avg 23 mpg
and 87 avg 23 mpg all hwy .

i think its based more on being easy when i hit the gas, because aggressive driving will yield me 18 -19 mpg on all fuels, and city is like 13-15mpg

 

like many others i get about 1 mpg less with 87
as far as overall economy using 91, 17mpg in the winter 19.5 mpg in the summer for 50/50 citi/hwy mix

 

Some of you guys are reporting some pretty good gas mileage. Makes me wonder is my 04 Sedan 6-spd F'ed up or are some of these claims exaggerated. I don't think I've ever seen over 18 MPG city in my sedan snce I've owned it in 03/05, what gives?

 

Perhaps driving style...how hard you accelerate and how often you brake/accelerate?

 

I have found similar results as these guys above. I did this test about 6 months after owning my car to figure out if I wanted to keep spending the extra $ for premium gas. In the end, it was a "wash" for me...buying higher octane gave me better mileage, but in the end, the cost for $ spent per mile driven was about the same....so I've been sticking w/ the premium gas ever since.

 

It's good to get data that people have collected, of course. But it's also difficult to establish statistical confidence in it. I'm a little skeptical that lower octane gasoline delivers lower MPG. In fact, lower octane gas probably has a higher fuel value because high octane additives (e.g. alcohols) have lower fuel value. The only thing the VQ engine knows about different gas is whether or not pinging occurs, and if it does, the timing gets retarded. This results in lower power (my guess - maybe 20-25 hp), and it might, might, cause lower mileage. I would expect that retarded timing only happens under extreme loading - i.e. when you are demanding > 200 Hp.

Just searching for a physics-based reason for getting higher mileage on lower octane.....

Here is my data for four grades of gas, over a period of four years:

87 (11 tanks): 19.2 MPG avg
89 (49 tanks): 18.7 MPG avg
91 (35 tanks): 18.2 MPG avg
93 (38 tanks): 18.6 MPG avg

 

Another variable to consider when calculating mpg, is summer blend vs. winter blend (atleast here in the Chicagoland area). I have been using premium on the G, but even on my 4 cyl. Accord, 87 octane winter blend gives roughly 10% worse gas mileage than the summer blend.

For the guy who has been getting really crappy mileage, I would check to make sure your tires are at the correct psi, air filter is clean and maybe clean out the trunk of unnecessary items. If those check out, it might be a case of lead foot.