Originally Posted by 4vxc
Shell will have a new 100 octane Optimax with 5% ethanol in the servos by christmas, sounds good except for the Ethanol content. They do not recommend it for use in boats or aircraft but do not say why.
Aircraft need a higher octane rating still, due to operating at higher altitudes where they lean out the mixtures a fair bit for economy and to keep the AFR right. Avgas has a 100/130 performance or octane rating.
Aircraft piston engines still require lead for their engine protection so it would be bad to use this new unleaded fuel......can't pull over onto the side of the road up there!! Avgas still uses lead addatives.