What is the difference between bus engines and car engines?

Answer 1

Usually the size, torque and power.

Buses are generally a lot heavier than cars, so they need stronger engines to be reasonably fast in traffic. Stronger engines tend to be bigger and heavier.

While sports cars can easily have higher (peak) power ratings than buses, bus engines are built to deliver more average power.

Fuel can also be a difference.

In some places almost all passenger cars run on gasoline/petrol, while almost all buses and heavy vehicles run on Diesel.

Expected life can also be a difference. Commercial vehicles are sometimes expected to last ten times as many miles as a regular car.