Posted by WD on July 22, 2003 at 08:30:08:
In Reply to: ? on high octane posted by Scott on July 22, 2003 at 03:23:29:
Where the gas is oxygenated year round, I run premium, otherwise 87 works alright. The main benefit if true racing gasolines is knock resistance for high 10.5:1 and up compression engines, or those with boost from a turbo or supercharger. It also seems to (for some unknown reason) offset some of the power lost to modern fuel additives. Many racing blends are still based on leaded fuel, which has better lubricating properties for the exhaust valve than unleaded fuel substitutes. When the exhaust valve moves freely at all RPM ranges, you get a scavenging affect which will clear more of the combustion chamber, allowing more fuel and air to bepacked in on the next intake stroke. More fuel plus more air equals more power, up to the limits of your engines combustion chamber design. Modern HD's supposedly run just fine on unleaded, but my late wife's EVO (prior to my curent wife Lisa for those who know her, she's fine) ran best on leaded aviation fuel. Your friend is trying to compensate or HD's primitive cylinder head styling. The Savage works fine on unleaded, I've run leaded to se what happens, no change in power output, but the exhaust sure gets hotter. Stick to whatever range of unleaded your bike likes best. Try other brands, some bikes are fussy.
-WD