Originally Posted by
43Inches
The only way an AVGAS replacement will be cheaper than AVTUR is if there is some huge change in the way it is refined, dropping lead is a start, but that might make refining a longer more expensive process making in more expensive again.
It's not the refining cost, it's the testing & paperwork cost - after all this is aviation we're talking about here. Car fuel is, let's just say, a little less stringent.
By definition, AVGAS* without TEL isn't AVGAS, hence the significant cost-and-time hassles GAMI had to go through to generate STCs for every engine type their customers want to run their G100UL (G = GAMI) on - even through it's (supposedly) a drop-in replacement. That means that, at airports in the states where only G100UL is available, if you haven't obtained (paid for) an STC in advance you can't, legally, refuel your aircraft there.
*For standard AVGAS, start at ASTM D910-21
Standard Specification for Leaded Aviation Gasolines
The gasoline shall adhere to octane rating requirements specified for individual grades, as follows: lean mixture knock value (motor octane number and aviation lean rating); rich mixture knock value (octane and performance number); tetraethyl lead content; color; and dye content (blue, yellow, red, and orange). Conversely, the gasoline shall meet the following requirements specified for all grades: density; distillation (initial and final boiling points, fuel evaporated, evaporated temperatures); recovery, residue, and loss volume; vapor pressure; freezing point; sulfur content; net heat of combustion; copper strip corrosion; oxidation stability (potential gum and lead precipitate); volume change during water reaction; and electrical conductivity.