The engine used in the original VW Beetle was about 40 HP (started out even less, and later models were 60 HP, but for many years it was 40). I have heard that

The engine used in the original VW Beetle was about 40 HP (started out even less, and later models were 60 HP, but for many years it was 40). I have heard that it only takes about 18 HP to overcome air resistance at highway speeds for a small car. Also, it's important to note the reason for the big discrepancy between the "inflated" horsepower ratings modern cars have vs. the lower HP in older classic cars: power is RPM * torque, and gas engines are rated in peak horsepower. To reach the advertised peak horsepower of modern engines, you have to be fairly high RPM (5K to 6K) whereas an older, lower horsepower rated engine might start to drop off its power curve after 4K. But at lower RPM the torques may be similar, or even higher for some older engines (the VW engine in particular with its Boxer configuration was optimized to have good torque for its size). What this means is that unless you are driving full throttle all the time at high RPM, you're not necessarily pushing all 100+ horsepower or whatever that your modern engine is capable of in theory, and so conversely an engine with smaller max horsepower is not as much worse as you'd think it would be.