92/93 octane in the Harley, the timing is very advanced on Harleys, and 87 octane in the Honda, the timing is very mild. The lowest usable octane, without knock, will give you the best performance since it's more combustible.

 

Yes the lowest octane w/o knock will yield the best power but any tips on how to tell if your engine is knocking, other than feeling "sluggish" because of the automatic retarding?

 

Automatic retarding? You kids and your new fangled computer-controlled vehicles! I, personally, can tell knocking because the engine knocks

 

yeah technology spoils us. Im not sure if motorcycles now are equipped with such devices but since cars are I wouldn't see why motorcycles wouldn't be. Their engines are way more advanced than a cars IMO.

 

Yeah, they're more advanced... pfffft. I doubt they have knock sensors considering that fuel injection is still a somewhat new idea to bikes, but if they do, I guess the only way to tell if you're knocking is to hook a computer up like you do with a car. I know that every bike I've owned has been carbureted though, so knocking is pretty obvious.

 

i say they are more advance because conserdering their displacment/stroke they make a lot of power.

 

ok if this is tru ..then why do they have race gas?.. 100 octane? i still dont belive this.. just for the fact if it was true ppl wouldnt run race gas. they would run sum low ass octane

 

High Compresson, Turbo Charged or other Forced Air Induction Vehicles require higher octane (cooler burning fuel) to protect against detenation.

 

Yup, like Cecil said. High compression, advanced timing, forced induction. The more Octane vs. Hectane in an engine, the less volatile it is meaning less pre-ignition detonation.

Here, you guys should read this:
http://science.howstuffworks.com/gasoline.htm

 

That's true. They do generate a lot of horsepower for their size. Car engines could easlily generate the same, but with more mass, more weight, and more horsepower, it's just more expensive. That's why you don't see a lot of cars stock with small displacement/big HP motors.

For example, my Magna is a 748cc (45ci) V4 running about 90hp. That's roughly 2 HP per cubic inch. It's totally feasible for me to run 650hp, normally aspirated, out of my 327ci SBC, but, it'd cost a hell of a lot more than the Magna motor.