My initial thoughts

[oldqwerty]

Originally Posted by Weldangrind

That was an excellent explanation.

I realize that I failed to ask my question properly. I knew that Ethanol only has a fraction of the potential energy of gasoline, but I thought the number was closer to propane, which I think is around 80%. In Canada, we went through these issues in the '80's, when our gov't offered rebates to those who would have propane conversions performed. The only reason that propane seemed to be more efficient was that is was far less expensive than gasoline in the beginning. Then the price started creeping up...

The question I meant to ask was, is there an octane sweet spot for straight gasoline for modern cars and trucks? I ask that knowing that some vehicles require premium, but I'm not interested in that info. I'd like to know your thoughts about everyday passenger vehicles that run on regular.

87, unless at high altitudes. 85 at high altitudes. Make sure the octane rating is (R+M)/2. Some places use different definitions of "octane rating."

Many engines loose power and efficiency as octane ratings go up because the slower flame front propagation does not allow peak cylinder pressure early enough in the combustion stroke.

Tdub (stock engine with rejet) lost power slightly over 88 octane, exponentially.

Tdub2 (267cc EFI, 11.6:1 compression, timing advanced 4* with ping sensor and ignition retard to run 87 when necessary) gains power with up to 97 octane, then levels off.

Pirate (276cc carbed, 12.7:1 compression) requires 93, and really likes 103. My son put 87 in Pirate, rode 1/4 mile, shut the bike off and pushed it home. It pinged so bad he thought he had blown the engine.

To vary octane we started with 87 E0 and added toluene, a common octane booster and paint thinner.