A number that describes a physical quantity is meaningless unless the units of measure are given. If we have a length of 20, we don't know if it's 20 meters, 20 feet, or 20 light years. Despite this fact, there are no units specified in Vamos.
Consider the fundamental quantities to be time, length, and mass. From these, you can derive the units for any quantity used in the simulation. For instance, the units on velocity are a length unit divided by a time unit. Force units are mass times length divided by time squared. As long as the fundamental and derived units are consistent, it does not matter what base units are used.
There's one exception. Since the simulation relies on library functions for timing information, and these libraries use seconds, the unit of time must be seconds.
I always use SI (metric) units because it's easy to keep the base and derived units consistent. The SI base units are the meter (m) for length and kilogram (kg) for mass. Power is derived quantity with units of Watts. A Watt is a kg*m^2/s^3. If you use feet and slugs as your base unit, then your power will be in slug*ft^2/s^3; you can't simply use horsepower.
Derived units used in the simulation are
There are some places where non-SI units are used. All angles are specified in degrees. Engine speeds are specified in rotations per minute (RPM). The coefficients for tire friction have their customary units.