Thread: Octane
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Old 09-06-2011, 12:54 PM
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Greybeard Greybeard is offline
Motorized Bicycle Elite Member
Join Date: Feb 2011
Location: Sequim WA
Posts: 336
Default Re: Octane

I've spent 50 years with racing 2 strokes, and large 4 stroke engines. Have seen just about every type of failure possible, and the majority of them have to do with detonation.
When I see post after post about head gasket failures, it makes me wonder if the "conventional wisdom" is wisdom at all. Any engine, when working against high heat, excessive timing, or too low of octane, will detonate under high load. Most of these little engines are running at WOT more than any thing else. Higher octane reduces the speed of the burn, which in turn reduces the maximim cylinder pressure the engine has to contain. Too fast a burn and cylinder pressures spike, blowing head gaskets, pulling studs, breaking rings and pistons. High temps increase the odds of uncontrolled burn and high cylinder pressure.
An engine that is on the verge of detonation is running high cylinder pressure which will make good power until it breaks. Higher octane won't make more power, it's value is a more controlled burn.
You don't hear detonation. In some cases you can feel it. A racing smallblock Chevy will lose it's smoothness, you'll feel it and hear it as roughness or vibration.
There's an old saying, before my time, that "the poor can't afford to buy cheap". If you have lots of money and can afford to fix or replace what you have, it doesn't matter what octane, or kind of oil, or % of mix you use. If you rely on your equipment, can't afford the breakdown, my opinion is to not try to save 20cents on a tank of fuel.
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