Just noticed while reviewing some old magazine. Quoting AAA magazine Nov/Dec 2005 page 32

"If you think fuel efficiency is boring, these are the cars that will change your mind. Both the coupe (28 city/36 highway) and teh convertible (27 city/35 highway) were designed to use premium fuel, but they will run just fine - albeit with a slight loss in performance - on regular gas".

Somebody straighten these people out?

 

AAA Magazine is run by sensible, boring people, who all probably drive Honda Civics and Toyota Camrays. Ignore those kill-joys!

 

But I'm finding that not only do you loose performance, but you also loose gas milage too! Retarding the timing does prevent the detonation, but it also takes a big chunk out of efficiency as well.

Matt

 

The 28/36 estimates appear to wildly variable from car to car as well.

 

I agree with Dr Obnxs.

Using a lower octane fuel will decrease your gas mileage. You'll find you spend more money filling up with 87 octane. Even if the the cost per tank is a couple of dollars less, you fill up a lot more.

 

I ran more than a dozen tankfuls of 89 octane through my MC this winter, and comparing the gas mileage before and after (weather and driving conditions were the same), I realized that the $.10-.12 per gallon I saved from the cheaper gas cost me about 2 mpg on average, and offset the savings almost exactly. I'll probably just stick with 93 octane from here on out since 89 octane wasn't any less expensive when the loss of mpg was figured in. I've never tried 87 octane in the car.

-Keith

 

In colder weather you might be able to get by with a lower octane rating, but as stated by others above it'll do more harm than good normally.

 

Well, the MINI manual states clearly that they are to be fueled with a minimum of 91 octane, so that is what I believe is best for our MINIs.

I, too, have experimented a bit with the lower octane, but only when out of Cali, (which sells 91 octane premium fuel), and in higher-octane states to balance out the octane number. My mileage went down...

 

The engine will retard and run like crap, spend the extra 2 bucks

-alpinamike

 

I accidentally put a quarter of a tank of 87 in and my car felt so bogged, so I filled the rest up with 94, feels better now

 

"Excuse me sir? Your horse has been dead for some time, might we use the glue it is turning into??"


"Absolutely not, I'm not done beating it yet!"

 

"will run just fine - albeit with a slight loss in performance"
I wonder what the benchmark car is they are using for caparison with this statement...A K-car.
Don't worry about that sluggish feeling, pinging nocking and increased wear "it will run just fine"

 

alright, there is nothing wrong with using lower octane in your car. on a few conditions, if you live at high altitude by all means save your self a few bucks and use the cheap stuff because using high octane wont do you any good. If your running higher then normal boost then high octane if good. another is many gas stations are using crap gas, most of the higher octane stuff has more ethanol in it, which has less energy to it, thus you will get worse gas mileage off any gas that has more ethanol in it. this could also be why many people get different dyno #'s all the time, because the gas they are using has different levels of ethanol in it. I have talked to some mini mechanics in utah and in portland, they both say that the cars actually run better on lower octane and with my own experimenting i find this not to be false, but i do know that the minis that stutter on start up don't stutter with lower octane. most of you people who say that its horrible putting lower octane in your car probably don't know much in the science department.

 

Actually, *****, this topic has been discussed ever since 2002. Not necessary to tell us we don't know much in the science department.

 

But it's true. Why straighten them out?

 

as it is counter to all the testing I've done.

Matt

 

I may not know much in the science department, but I know real world results, and after carefully calculating virtually every tank of gas for the last 9000+ miles in my MC, I can say with authority that my MC gets better gas mileage with 93 octane than it does with 89 octane. I fill up about once a week at the same gas station, and my commute doesn't vary.

 

What are your qualifications?

 

Just FYI, you might want to actually learn who people are here prior to calling them out. (i.e. Dr. Obnxs)

 

Some observations from running different grades of gas in my MCS

Regular unleaded- cheapest fuel
Least performance but will work OK
No ill effects on start up or for regular driving.
Slightly less mpg.

Premium unleaded- costs more but makes my MINI happy
Most performance on demand
Works fine for daily driving
Best mpg- if I could only drive the speed limit.

So it seems to me that if the cheaper gas gives less mpg and less performance with the possibility of detriment to the life of the engine and possible hard starting/stumbling then...

Give me Premium please!

And that is what I do.
So I drive mostly with good mpg in mind but I know I have
POWER on demand should I need it (want it).

 

so we may actually be able to learn from others...

I haven't found good results with low octane gas, but I don't live at a realy high altitude, and the gas I have access to actually sucks pretty bad (other than the real expensive race stuff).

Matt

ps, But thanks for the vote of confidence!

 

Matt-

I just know when someone has way more car knowledge than I. All you input here and in MC2 is appreciated!

 

Since I am one of the scientifically challenged I will start with some of the basics that I can understand...
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. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.
A higher octane rating means the fuel is less likely to cause your engine to knock or ping. Instead of a controlled burn, you get what amounts to an explosion--not a good thing for your engine. To avoid this, high-octane gas is formulated to burn slower than regular, making it less likely to ignite without benefit of spark.
Car engines nowadays contain knock sensors that detect detonation and automatically retard the spark to compensate. The delay means maximum gas expansion occurs when the piston is farther along in its downstroke and thus there's more room in the cylinder head. This reduces peak cylinder pressure, eliminating knock but also giving you less power and poorer mileage.
So, thanks to the great engine management we enjoy in our Mini's one can get away with running lower octane fuel, and it will run just fine.
BUT WHY DID YOU BUY AN S?
BTW –the Roots type supercharger is an external compression supercharger but increases compression none-the-less.

 

actually i did mention altitude as a condition that it is fine to run lower octane (i use 89-91 at high altitude) the reason is, that there is less atmospheric pressure at high altitude, meaning that you will not get the PSI levels that you can get at lower altitudes. at 6000 ft you should be running around 3 PSI less then at sea level.

 

so then it's how much boost you're running that tells if you're gonna get retard. I've seen some data from a stock S showing some retard on premium (don't know if it was 91 or 93) so I guess with any pully it can be an issue...

Matt