These so called engine cleaners can only work on the pre combustion side of the engine.....which means the injectors ONLY.
The injectors are placed jsut before the inlet valve so from there to the chamber is about 4-6" at most...and thats the only part it will clean, all the tacky grimy oil vapour mess in the inlet manifold remains.
Only good for injectors, and its not a great cleaner either.