You cannot buy lead "additives" TEL (Tetra Ethyl Lead) is not available anyplace except in some racing fuels (like "Trick Gas" etc) and AVGAS.

100LL Avgas contains 2ml of TEL per gallon. TEL is only manufactured by one company. It is ONLY sold to AVGAS refiners and racing/specialty fuel marketing companies.

Any aftermarket additive bought "over-the-counter" contains NO TEL. There's probably other fuel "additives" available but I wouldn't waste money on any of those snake-oils.

They've all been tried by Consumer Reports and the results were basically that they did more for the seller than the buyer......... (They suck money out of your wallet and for those that placebos work well on, made them "feel" good)

 

Contrary to what a lot of people think, lead (TEL) was not good for engines, it was only good for octane. Lead deposits on valve seats corroded the seat material. It also made the god-awful sludge we find in old engines.

 

Yeah! It is particularly bad in some lower compression and low HP aircraft engines. So bad that Lycoming suggests using an FAA approved fuel additive additive that is supposed to reduce lead fouling of the plugs and combustion chambers in low compression non-turbocharged engines.

Non-leaded Autogas (AKA MOGAS) in (STC approved) aircraft engines completely eliminates the problem altogether.

Same thing happens in automotive engines too. But it's not nearly as bad since the engines are able to run MUCH leaner so the deposits aren't as severe.....