*Water-Cooled VW Performance Handbook*

# Horsepower and air flow

The gasoline motor is basically an air pump: The more air that flows through it, the more horsepower it makes.

## Estimating air flow by horsepower

If you know how much horsepower your motor makes, you can estimate its air flow in cubic feet per minute (CFM).

For example, a 1,600 cc motor in a good state of tune requires about 54 cubic feet per minute to make 78 horsepower.

This calculator uses the formula:

\[Air\ flow\ (CFM) = (Horsepower \times 0.625) \times 1.1104\]

## Estimating horsepower by air flow

If you have access to a flow bench, you can measure how much air flow you get through your intake and cylinder head. From this figure, you can calculate horsepower.

For example, the head on a stock 1,600 cc engine flows about 61 CFM. Therefore, the most you could expect with bolt-on modifications would be about 88 horsepower.

This calculator makes use of the formula:

\[Horsepower = (Air\ flow \times 1.6) \times 0.9\]