I was allowing a little extra for oomph on acceleration, as well as some loss from translation of the heat energy to vehicle motion.
Yeah, you are right, if you are talking kilowatts of heat, 100 may be marginal, I was thinking kilowatts of electric output, my mistake not yours.
Depending on temperatures, you may need several hundred kilowatts of heat to run a car, Carnot efficiency is lousy at lower temps.
The good news is that you wouldn’t have to worry about freezing to death in your car even if it doesn’t run like a sports car.