Re: Price of gas!!!
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: uhcoog1</div><div class="ubbcode-body">Static compression is not the best indicator of octane needed (though it's a piece of the equation).
For those that don't know, octane rating is just the fuel's ability to resist detonating before your spark plug goes off. Fuel will ignite itself when under enough heat and pressure, and 87 octane will ignite under less pressure/heat than 93, etc.
Burn rate is different than octane ratings, and is what is responsible for increased or decreased power. The fuel mixture used to "make" the gas you buy is what determines the burn rate, which affects power. Most real world tests show what you found, arctic, that the lower octane mixes have a higher burn rate.
Switchblade is right, a good rule of thumb is 10:1 and up needs 93 for iron heads, and 11:1 with aluminum. This is assuming the correct cam is chosen for that compression, adequate quench is achieved, and tuning is spot on.
Dynamic compression is the most important number for what ictane fuel you need. It's also the number I wish I knew about before I built my engine. It takes into account the bore, stroke, and when the intake valve closes after bottom dead center. Here's an article about it:
http://www.empirenet.com/pkelley2/DynamicCR.html
and a calculator:
http://www.wallaceracing.com/dynamic-cr.php
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Check out the big brain on Brad! You're a smart motherfu**er, that's right!