Yes. Carbon build-up can cause an increase in an engine's compression ratio. This is not a good thing. As an engine operates, carbon deposits may form in places such as the valves, ports, pistons, head gasket and piston rings. This carbon can interfere with normal combustion is several ways. It can alter the engines operating temperature, compression ratio, and several other important factors involved with combustion and sensor readings. The carbon build-up decreases the amount of space that is available in the combustion chamber. This increases the compression, which can cause the engine to overheat, ping (detonate), and also causes an increase in NOX emissions. Due to the fact that the carbon can retain oxygen from the combustion process, it can cause another interesting effect that can cause the vehicle to either trigger a light or fail an emissions test. It should also be recognized that if the carbon buildup is on the piston rings or ring grooves, it can prevent the rings from sealing properly, creating the opposite effect- low compression. Despite cleaning additives in Top Tier gasolines, chemical decarbonization is a good preventative maintenance procedure for engines having more than 35,000 miles. It involves running a chemical compound, along with the fuel, through the engine to breakdown any carbon deposits. They then get flushed out along with the exhaust gases. There are a couple of ways in which this is done. One way is to add the chemical along with some fuel in a separate unit that is connected to the fuel intake line on the car. The engine is started and the car is allowed to run for 15-20 minutes or until the mixture is fully utilized. This applies to both gasoline and diesel engines. This method of decarbonizing the engine is preventive maintenance. It will prevent carbon build up in the engine and keep it clean, increasing its life. For engines that have severe carbon build-up, a chemical decarbonization won’t be as effective. In this case, one will need to do a physical decarbonization procedure. This involves a time-consuming and costly procedure that involves opening up the cylinder head, removing the intake and exhaust valves and physically “scrapping” the carbon deposits off the valves, cylinder head and manifolds. The exhaust pipe will also need to be dismantled and cleaned thoroughly.