lead substitute fuel additive

[Pointparty@aol.com]

Year ago I had the head of my 71 mgbgt redone to accomodate premium 93 octane 
unleaded gasoline.  But, several years ago I began adding a lead subsitute from 
time to time when filling up.  

My experience has been good as far as I can tell, without any harmful effects, 
and increased power at interstate speeds, but I am wondering what the list 
wisdom says.

Any one?  thanks!........mel