The theoretical limit is 50% according to Wikipedia, but there's other factors being optimized for as well aside from efficiency: https://en.wikipedia.org/wiki

The theoretical limit is 50% according to Wikipedia, but there's other factors being optimized for as well aside from efficiency: https://en.wikipedia.org/wiki/Engine_efficiency#:~:text=Modern%20gasoline%20engines%20have%20a,of%20higher%20wear%20and%20emissions https://en.wikipedia.org/wiki/Engine_efficiency#:~:text=Mode....