A quick check on wikipedia quotes: "Current aircraft engines feature valve gear components which are designed for compatibility with the leaded ASTM D910 fuels

A quick check on wikipedia quotes: "Current aircraft engines feature valve gear components which are designed for compatibility with the leaded ASTM D910 fuels. In such fuels, the lead acts as a lubricant, coating the contact areas between the valve, guide, and seat. The use of unleaded auto fuels with engines designed for leaded fuels can result in excessive exhaust valve seat wear due to the lack of lead. The result can be remarkable, with cylinder performance deteriorating to unacceptable levels in under 10 hours." https://web.archive.org/web/20120413123438/http://www.tcmlink.com:80/visitors/carenfeed/engoperhdr.cfm https://web.archive.org/web/20120413123438/http://www.tcmlin... Also lead is an anti-knock agent so it is used to get to the very high octane ratings in Avgas. And it seems the problem may be solved soon! "By May 2012, the US Federal Aviation Administration (FAA Unleaded Avgas Transition rulemaking committee) had put together a plan in conjunction with industry to replace leaded avgas with an unleaded alternative within 11 years. Given the progress already made on 100SF and G100UL, the replacement time might be shorter than that 2023 estimate." https://en.wikipedia.org/wiki/Avgas https://en.wikipedia.org/wiki/Avgas