"stoichiometric"
For who ever asked is a fancy name for a balanced fuel air ratio.
So for every 2 H atoms there is 1 O available ( and no more) and for every C atom there are 2 O atoms available, no more.
So you consume all of the fuel with the available oxadizing agent ( usually oxygen).
And in theory you unleash all of the available energy from the fuel.
Most of the "lead substitutes" that you pour into your fuel tank are not there to stop valve recession or provide any sort of lubrication. What they actually are is anti-knock additives or pseudo octane enhansers