In a gas engine with traditional injection—port fuel injection or “PFI,” for instance—the gas and any fuel additives are atomized inside the intake manifold, pass over the intake valve, and into the combustion chamber.  That’s the configuration on the left—the yellow injector is “above” both the intake valve and combustion chamber.  Think of the intake valve as a combination air and gasoline intake valve, which makes cleaning possible with an in-tank additive.

In a direct injection or GDI engine, the fuel injectors are inside the combustion chamber.  That means gas and fuel additives can still clean the injectors and combustion chambers, but the intake valve is excluded from the process.  That’s the configuration on the right—the yellow injector is “below” the intake valve.  In effect, it is only an air intake valve, so cleaning it means removing of the cylinder head, i.e. disassembly, or cleaning by way of the intake air.
 

Berryman Intake Valve & Combustion Chamber Cleaner (part #2611) is designed to deliver a cleaning solution to the intake valve by way of the air stream.  In short, the product injects the cleaner at the throttle body (or via the engine vacuum system, which is more complicated to explain), and the air stream and cleaner mixture are transported through the intake manifold, past the intake valve, and into the combustion chamber, cleaning everything along the way.

Hope this helps.  If you have any additional questions, feel free to give us a call.