What is a common characteristic of high compression engines?

High compression engines typically require a magneto to provide the necessary ignition spark. A magneto is a self-contained ignition system that generates electrical power independent of a battery. This is particularly important for high compression engines, as they need a strong and reliable spark to ignite the fuel-air mixture effectively.

In these engines, the fuel-air mixture is compressed to a higher ratio before ignition, which increases the likelihood of pre-ignition or misfires if the spark is not strong enough. Therefore, a magneto system is advantageous because it can produce a high-voltage spark which is more reliable under these demanding conditions.

The other factors mentioned in the options either do not pertain specifically to high compression engines or are not necessary for their operation, reinforcing the importance and relevance of using a magneto in such applications.