The McLaren road cars, almost all of them (P1, MP4-12C 650, LT750, 570) had the Tom Walkinshaw 3.8 L engine he designed for an Indy Racing League car. But Indy Racing League and Indy Car combined on the alcohol engine formula and the engine had no home. McLaren licensed the engine for their road cars and have only recently altered it for a 4.0L design for the 720S and Senna.
I am specing a 570S car right now.