Aaron Coolidge wrote:

I paid $2.29 for 93 octane premium unleaded in Mansfield the other day.
I paid $2.60 for 100LL in Columbia County, NY (1B1) the other day.
For me, the math is self evident, but the other way! (Break even with STC
costs @ 10000 gallons or 1000 hours!)

Something is wrong with your math.

@ $0.31 price difference per gallon, it would only take 741 gallons to
pay for the $230 STC (O470, 230HP, $1 per HP).

My price difference between 100LL and 86 Octane autogas has typically been
$0.75 to $1 per gallon. I figure that between overhauls of my engine (~2000
hours, buring 12 gph), I saved a minimum of 12 * 2000 * 0.75 = $18,000,
which is what the last overhaul cost...

MikeM