Subject: Re: Lead replacement fuel additives. Necessary?
Tetraethyl lead was apparently introduced during the 1920s, so it would not be safe to assume engines built then or later would run unaffected by no-lead petrol. That said, metallurgy doubtless improved over time. Consider how long it takes a modern engine to need a rebore, compared to those of "our" era.
The issue is valve seat recession, however the (modern) engine chosen (probably deliberately) to test the effects was particularly prone to this wear. So although it certainly proved recession could occur, it probably also illustrated a worst case scenario.
I don't use additives in my LG6 (Meadows engine), and have note no ill effects, although I do run it on 98 octane solely because I understand that contains less ethanol.
My other car is a 1951 Riley RMB, engine very much a prewar design. Still finalising the restoration of that, but I do have friends covering prodigious mileages (one averages 24000 miles a year) in their Rileys, without using additives. They have encountered no problems.
The concensus appears to be that recession is only likely to be an issue with engines of our era where sustained high rpm is used. So perhaps a concern if you are racing.
At the end of the day, all you need to do is check your tappet clearances. If you find those are closing up unduly, then it would be an idea to try additives.
Laurence