Originally Posted by nunyo

My $0.02.

I've done a little bit of testing on this vein of thought with my commuter car. I find that if I keep the rpms down under 4K in each gear and don't acelerate too hard to 4K RPM I can get the most out of each gallon of gas. Of course, when I do that, I'm rolling around slower than your grandma everywhere I go.

On your typical fuel injection setup the throttle controls how much air gets into the intak manifold and the computer decides how much fuel it should inject to keep the AFR correct. Less air, less fuel. Less RPMs, less frequent delivery of fuel. If you were to plot fuel consumption by throttle position (% open) and fuel consumption by RPM, there's be an intersection of the two graphs at which point you'd have the optimum throttle position and RPM given the diameter of your throttle body.

Originally Posted by TheShow50h

Mine runs perfectly fine on 87, but I run 89 to give me a little cushion most of the time just in case there is detonation that I'm not hearing while running 87.

The reason some people run 100+ octane is because that is how there engine setup was designed... some engine setups make way too much cylinder pressure to be able to run 93, so they need a colder burning fuel (for instance, high boost/compression/nitrous). Run a tank of 89 through your bike Jeremy and see how it does. The best way to test if it's running fine will be to put it in high gear and romp it from a real low rpm to put the engine under a lot of load, you should hear any detonation... you'll know it when you hear it.

Btw, your car, same thing. Unless your timing has been advanced you should be able to run 87 all day... remember, i know a little bit about the 5.0s and how to make them fast.

Originally Posted by Jeremy2792

Ok, so the compression ratio for the engine, bases the engine on what octane can, and cannot be put through the engine. High compression=Higher octane?

Originally Posted by Jeremy2792

Ok, so the compression ratio for the engine, bases the engine on what octane can, and cannot be put through the engine. High compression=Higher octane?

Originally Posted by Jeremy2792

Ohhh k. So just because I'm WOT doesn't mean I'm just pouring gas into my engine. The throttle controls the air, which then in return the computer controls the fuel. I'm starting to understand this concept better now.

Originally Posted by Cecil

Some Low Compression Engines also require higher octane to reduce the likelihood of detenation, such as Turbo applications.

My Red bike is happy with C16 and 110 octane (NON-OXYGENATED) fuels.

I ran 100 octane once, came on boost, and thus my avatar.

Originally Posted by Frankie

Correct-o-mundo. When you open the throttle, you're opening either the butterflies in the venturi(s) of the carburetor or the butterfly(s) in the throttle body of your intake runner. All that really does is let more air in, changing the vaccum pressure of the motor. On a carburetor, the accelerator pump compensates for this momentary lack of fuel (due to the influx of straight air) by using a plunger and shooting gas kinda like a super soaker. In fuel injectiong the MAP/MAF sensor tells the computer to shoot more fuel. Once the vacuum pressure evens out, the caburetor will feed gas normally through its jets. On fuel injection, the computer controls the fuel delivery.

Basically, remember these two things: When you hit the gas pedal, you're really only delivering air, and a carburetor is just a controlled fuel leak.

Originally Posted by Frankie

Exactly. My Harley is 8.5:1 compression, but with 34 degree advanced timing, I have to run 93 octane or it's ping city. On the other side of the coin, my 350 SBC is 8:1 compression and runs 12 degree advanced timing, so I can use 87 octane and still get decent performance.

Originally Posted by Jeremy2792

Awesome. I think I truly understand it now. Thanks man.

Originally Posted by Frankie

Basically, remember these two things: When you hit the gas pedal, you're really only delivering air, and a carburetor is just a controlled fuel leak.