Not exactly true. Some STCs require the use of 91 octane (or better)
autogas.

Very true. You've got to read the fine print in the STC. (Although, as I
understand it, there are very few STCs that actually specify "premium" car
gas.)

Your pathfinder uses the 235 hp low compression version of the the
O-540. The higher hp versions (250, 260, etc...) have a higher
compression ratio and require the use of high octane fuel.

Right. Which makes me wonder why they don't simply come out with an STC
that specifies the use of higher octane auto gas (as in the example, above),
rather than simply not having a mogas STC for the high-compression O-540.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"