Answer
A frictionless car engine is not 100 percent efficient, whether or not the engine runs on the Carnot cycle.
Work Step by Step
Equation 20.14 gives the efficiency of a Carnot engine: $e_{Carnot}=\frac{T_H-T_C}{T_H}$.
The cold reservoir temperature is greater than 0 K, so the efficiency of even a Carnot engine is less than 100 percent.
Carnot engine is at least as efficient as any heat engine, so even a frictionless car engine is not 100 percent efficient, whether or not the engine runs on the Carnot cycle.
