Originally Posted by Strongjeff
Diesel burns slower. Last time I checked 91 burns hotter then 87, its why you make better power and fuel mileage on a higher octane then a lower one. Burns hotter and gets a better burn over a lower rated fuel.
Higher octane needs more heat to light on fire. It doesn't necessarily burn hotter. As gas is compressed it heats up. When 87 is highly compressed it will explode before the spark plug goes off, a phenomenon known as detonation, that's when a higher octane is used. But to get any benefit out of it that fuel needs to be compressed more so that it can be burnt at a hotter temperature. On a stock motor, the 87 octane gas is not being compressed or "heated" enough to make it pre ignite and detonate.
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