The other day I dropped my car off at a European specialist shop, and while I was there, a technician was working in the engine bay of a Mk7 Golf R, cleaning out carbon deposits off the intake valves.

Every new car sold in the United States today uses fuel injection, but not all fuel injection systems are the same. Some cars use port injection, while others use direct injection. Some even use both.

As we entered into 2014, the industry was abuzz with the acronym “GDI,” otherwise known as Gasoline Direct Injection. The “gasoline” distinction is significant because direct injection has existed in ...