I’m already being super generous and giving you 1600 Watts of power on a footcrank to start, plus 140 W per point of ST over 8 You can actually power a car alternator with 1500 W, it’s just maximum effort for a normal human.
Manual engines produce 45% of their maximum output at safe levels, so ( 140 * ( ST - 8 ) + 1600 ) = 1500 / 0.45, solve for ST, and you need ST 21 to crank a car alternator without strain as a mutated superhuman.