Understanding Octane Ratings

[steelblue5505]

Bought gas today at a Conoco/Phillips station. At this particular filling station all their pumps advertise that they do not have entohol added.

Also by each pump's nozzle is a sign that declares Minimum Octane Rating
R+M/2 method. The octane rating of the gas I bought was 91.

Question: What is or does the formula mean, what is R what is M?

Anyone know?

[Peterfurlan]

Re: Understanding Octane Ratings

R is Ron and M is Mon want more Google it. Best answer is gas up and go don't ask any questions.

[Southern]

Re: Understanding Octane Ratings

Research Octane Number and Motor Octane Number - the formula arrives at a single number that indicates the maximum compression ratio vs the point at which "knocking" or pre-ignition will occur. In any event, their is a lot to be said for following John's suggestion.

No ethanol is a good thing IMO.
True, it adds a couple of points to the Octane Rating, but there are several environmental concerns.
I think the biggest reason we have ethanol is politics.

A good thing, without doubt, is Top Tier gasoline.
I have used it in all my cars since BMW came out in favor of it several years ago.

http://www.toptiergas.com/

[Tbyrdy]

Re: Understanding Octane Ratings

Bought gas today at a Conoco/Phillips station. At this particular filling station all their pumps advertise that they do not have entohol added.

Also by each pump's nozzle is a sign that declares Minimum Octane Rating
R+M/2 method. The octane rating of the gas I bought was 91.

Question: What is or does the formula mean, what is R what is M?

Anyone know?

Isn't 91 a bit low for our cars?

[Gobird]

Re: Understanding Octane Ratings

Jim, The sticker inside your gas door reads 91+.

[Tbyrdy]

Re: Understanding Octane Ratings

Jim, The sticker inside your gas door reads 91+.

Amen...but I never run lower than the max available at the pump...I thought everyone did!
Why squabble over a few pennies a gallon when your monster engine is just chomping at the bit for the better fuel?

[Southern]

Re: Understanding Octane Ratings

91 octane is the "normal" Premium rating.
Florida is one of the few states where 93 octane is the normal premium.

[Gobird]

Re: Understanding Octane Ratings

Yes, High Test usually runs between 91 and 93 now days. Mid grade is usually listed at 89 so you should be good with anything that is listed as premium grade.

[DaiUyTed]

Re: Understanding Octane Ratings

Amen...but I never run lower than the max available at the pump...I thought everyone did!
Why squabble over a few pennies a gallon when your monster engine is just chomping at the bit for the better fuel?

I squabble over a few pennies. That's how I was able to buy a used Tbird (with a very modest sized V8, about the smallest ever made), instead of settling for a used Corolla. But, I know you jest.

[Tbyrdy]

Re: Understanding Octane Ratings

I squabble over a few pennies. That's how I was able to buy a used Tbird (with a very modest sized V8, about the smallest ever made), instead of settling for a used Corolla. But, I know you jest.

I knew SOME joker would retort my penny comment!

[lmartun]

Re: Understanding Octane Ratings

91 octane is the "normal" Premium rating.
Florida is one of the few states where 93 octane is the normal premium.

In my home state, Illinois, we have 93 octane. I fill my TBird with BP, Mobil or Shell ONLY and in that order of preference.


Lou

[SixPac]

Re: Understanding Octane Ratings

In Mississippi, 93 Octane is the normal premium rating.

[FritsB]

Re: Understanding Octane Ratings

We run on 95 and 98 octane.
95 is regular.
The oldies run fine on both.

[Toystoretom]

Re: Understanding Octane Ratings

Frits... Your octane rating is probably measured differently than ours is. I talk to a Gent in Oz quite often and theirs is measured differently and the resulting numbers are quite a bit higher than ours. I'll bet it varies from country to country.

Tom

[Southern]

Re: Understanding Octane Ratings

Frits, Europe measures octane using the RON method. We (US) use the R+M/2. Your numbers will be higher for the same octane rating.

All of California, Nevada, and Arizona have only 91 octane as Premium gas.
For all practical purposes, there is no difference other than to say that there may be more ethanol in the 93 stuff.
Remember, all gasoline starts at the same point. They only refine one gasoline.

Then additives are added to raise the Octane rating and keep the system clean.
There is no more "power" in 93 Octane than there is in 87 octane as measured by BTU available.

But the 93 Octane allows the ECU to advance the timing of the engine without knocking, and yes, when you advance the timing, the engine produces more HP.
So there may be 7 or 8 more RWHP when comparing 93 to 91.
That few HP is insignificant and is largely theoretical since most dynamometers can't repeat the same readings twice.

What will happen if you use 89 octane in our Birds?
Nothing. I did it. No knock.The Senors and the ECU did what they are designed to do.
Possibly it might take a few tenths of a second more to get to 60MPH, but the engine will not knock and will not be damaged.
The ECU will retard the timing slightly to prevent knocking.

What about 87 octane?
I don't know.
The Ecu, combined with Knock Sensors, can adapt for less or more octane, but obviously there is a range limit.
I strongly suspect the car will run just fine on 87 octane (Tho give up a more significant amount of performance as the timing is retarded) but somebody else will have to test that theory! ;)

Anyway, running the "proper" octane rating in an engine will often only cost pennies.....and return a bit more power and a bit more MPG......thereby offsetting the few pennies.
In Florida I run 93.
When I go to CA I will run 91.