You can, but it's worth pointing out that cars don't really run on the Carnot cycle because, unlike your air conditioner, they're not reversible. Usually they use something like the Otto cycle. To improve efficiency you can change your cycle or push the limits (temperature, compression ratio, etc.). The current generation Prius apparently uses an Atkinson cycle and achieves 40% efficiency. Some F1 engines notably have a thermal efficiency of 47%.

https://arstechnica.com/cars/2016/05/turbulent-times-for-for...