[bullit4404]

When you pull up to the pump to buy gas, you are presented with choices.The octane rating of a fuel is the thing we see on the pump. 87, 89, 91, 93 and even 94 in some places.
What is Octane? Octane is a hydrocarbon that occurs as part of the gasoline refining process. It has 18 different popular variants that include combinations with Heptane, Hexane, Pentane and Butane. For the purposes of motor fuels Octane is the measure of resistence to ignition under pressure. So the higher the Octane number the greater the temperature at which it allows the fuel to release it's energy. Octane rating is not a measure of the energy contained in the fuel, just the temperature at which it goes BANG!
So, you won't get any more power from 91 Octane fuel unless your engine is optimized to take advantage. In fact, if you have a low compression engine and use 91 Octane fuel, you may actually get less performance, since the engine has to work harder to ignite the fuel.
What else is in gasoline? There are detergents, solvents, temperature stabilizers, proprietary additives and in most fuels Ethanol. Depending on your geographical location, your refiner may change your fuel formula several times a year to compensate for temperature and other environmental factors. Summer fuel has anti vapour lock additives and winter fuels are adjusted for lower temperatures etc.
Ethanol: The double edged sword. On one hand, adding ethanol makes gasoline burn cleaner, on the other it produces less energy than gasoline,(less BTU's per volume), so you use more. Pure Ethanol has higher Octane than gas (about 110), but once it's blended with gasoline the number on the pump is what it is. Remember Octane rating is not potential energy. Ethanol has some other less than desirable qualities. It is Hygroscopic, it attracts water. This is particularly a problem for seasonal and marine engines. Engines in storage for long periods can actually form biological growths in the fuel system (gunk,varnish, slime) and cause damage to organic gaskets and rubber components. Fuel stabilizers can help some, but they are only effective for a few months and must be well mixed with the stored fuel. Fuel stabilizers can possibly cause emission test failures (tailpipe emission tests) and should be run out of engines before testing.
Typically, gasoline (in Canada) has 10% ethanol in 87 fuel, 5% in 89 fuel, and 0% in 91 or higher Octane fuel.
I understand, on the west coast US those numbers are higher. So we generally only use premium in our recreational and seasonal equipment.
All major refiners produce about the same fuels. Gasoline comes out of the refinery as regular or premium fuel, and the additive packages are added as it is loaded for delivery. At your local gas station, there are usually two tanks, or sets of two, one for regular and one for premium, and it is mixed at the pump depending on your choice. Why is premium so much more money than regular. Well, aside from the fact we're being hosed at the pump, they sell a lot less premium fuel. Racing gas is a whole different discussion, is very unstable and must be kept out of direct sunlight or it can start to separate in hours. It's also expensive. With the Trans Am cars, we typically blew through $500 a weekend in fuel. (2+ fill ups 22 gallon fuel cell)
You know what they say;"If you want to make a small fortune in racing, best to start with a large fortune.
Questions, comments, likes? Good day all!

 

[bullit4404]

Apparently, SUNOCO racing fuel has 15% Ethanol.

 

[tossass4370]

The neat thing about the "08-09 Bullitt is that it has an adaptive tune that senses when knock develops and adjusts the ECM. So you can run 87-93 octane and realize the results. 87 for cheaper highway cruising and 93 for track days with more HP.

 

[TrueBlue02058]

I Run 91 in the BULLITT and all motorized equipment at home, Snow Blower, Generator, Lawn Tractor and Mower.

I put 87 in the F-150 and Mazda CX3. But the Mazda Engine has a Compression ratio of 13 to 1 (Sky Active Technology). It is naturally aspirated and doesn't call for 91 Octane.

 

[JackDW - 852]

Thanks Pat for another very informative posting.

A look into the past. When the automakers started adding the EGR system to their engines. This was shortly after they had removed the lead from the gas. It seems everyone wanted to remove the ERG system, mostly because they did not understand it. Myself, I disconnected it from my Monte Carlo (350 V8 ). I immediately saw a reduction in my MPG and the engine started to do a lot of pinging, so I hooked it back up. When I started looking into this a local mechanic explained what was happening.

As you explained above "Octane is the measure of resistance to ignition under pressure". What the EGR system was doing was adding some of the burned exhaust back into the intake system. This basically increased the Octane of the gas (increased measure of resistance to ignition under pressure). According to the mechanic, this was not really a planned results of the EGR systems but was a beneficial side effect of this system. So, for most people, it was better to leave that system in place. It helped MPG by increasing Octane, not hurt it.

If you knew what you were doing, the system could be disconnected as long as you make tuning adjustment, timing, etc and you could gain better MPG. But most people I know (back then, we were mostly teenagers) just tried to pull anything they thought was emissions related and did more harm than good.

I am sure there are a number of people on this site that remembers those days. In some cases, we were really dumb about things, but you would have never convinced us of that back then. >

 

[bullit4404]

Thanks for the trip down memory lane Jack. I had a 77 Camaro and I cut off the Cat. converter and pulled the nozzle reducer out of the filler pipe for the gas tank. It ran better on leaded fuel, but in retrospect I was not helping the environment.
My 67 Mustang had an early PCV system and fouled the plugs so bad I had to clean them every couple of weeks. Lousy valve seals didn't help. Ah, the good old days.