Quote Originally Posted by rwanttaja View Post
Not quite as simple as that. They were certified for 80 octane LEADED fuel. IIRC, the lead acts as a lubricant on valve guides, etc. 100 "Low Lead" fuel has four times the lead as the old 80 octane, which for many engines, is too much of a good thing.

I run my C85 on unleaded car gas in the summer, but switch to 100LL in the fall due to gas-stability issues. It seems to handle the mixed diet.

Ron Wanttaja
My understanding is that it is indeed that simple. If lead is needed as a lubricant, then we are all going to be in trouble when (and if) unleaded 100 octane is ever created and replaces 100LL.

From the SWIFT website describing UL94:
"This proprietary unleaded fuel formulation is a blend of hydrocarbons designed to meet the fuel specification standards of ASTM D7592, D7547, and D4814. This fuel is FAA-certified for use in up to 65% of the US piston fleet; up to 100,000 aircraft are already certified to use the fuel based upon existing Type Certificates and/or Autogas STC's. An additional 25,000+ aircraft, those whose engines are rated for minimum Grade 91/96 Avgas, are eligible to purchase an FAA Supplemental Type Certificate (STC) for the use of Unleaded UL94 Avgas."