T.E.L (tetra ethyl lead) is a det retardant,the offshoot was lead deposits that helped the valve seats,all alloy headed engines,even with leaded fuel, have had seat inserts for years,ally does not like glowing valves seating on it...tends to melt!!!!My Jag has a 3.4 DOHC Straight 6 XK motor ,hemi-chambers BIG valves AND INSERTS...it was built in 1953!!!!!
