Originally Posted by FastbackTom
I attended a fuel seminar at Sema about 10 yeas ago... the guy was the NASCAR liaison from Unical, and offered up some real good advice (for us non-chemist-types) on race fuels in general. I've also learned a lot from my own experience with dynoing my own engines, talking with engine builders about various compression ratios and cranking compressions. I also have a fair amount of experience with VP's C12, and a little with C14 and C14+. My current engine is built around VP's C12, the mandated spec fuel for this other class I run (outside of NHRA SS).
-Quality gasoline contains the same number of BTUs per gallon regardless of octane. Higher octane does not mean more power (a common misconception)
-Octane is a measure of burn rate, or the way I view it, burn retardant. All things being equal, the higher the octane number, the slower the burn.
-Higher dynamic compression speeds up burn rate. A high compression engine with a cam that has lots of duration my have a lower dynamic compression ratio than you think. Cranking compression, measured with a traditional (quality) compression tester, is a decent way to determine dynamic compression on a normally aspirated engine.
-The simple way I look at octane; the best octane for my engine is the lowest that doesn't allow it to it knock.
-Too high an octane will make it lazy, and not want to rev up
-use sealed containers, drain your fuel after a race weekend... The chemicals that increase octane by retarding burn rate, are the lightest in the mix. They tend to 'boil off' at room temperature, lowering it's octane rating.
-UV light also has a negative effect on race gasoline. Those opaque poly fuel jugs allow UV to get through, I've been advised to use the colored ones that block UV, and store them out of direct sunlight. Also, poly jugs are not a perfect seal, the lighter chemicals will seep through poly jug material, when heated pressurize the cap and make it leak, and the vapor escape when you open the cap.
-The 2-valve wedge head engines I play with will not run on VPC12 with 300psi on cranking compression without rattling, but when brought back to 250psi, they will run on C12. Realize that's only one data point for one type of engine, but it may be an indicator of octane required for 250psi cranking compression.
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