Price, ingenuity, and reliability there are many reasons that the new FRS/BRZ is hallmarked as the revolution/ re-ignition of the RWD platform. One of the many reasons that the BRZ/FRS has been billed as the “dream machine” by many is due to its innovative D4-S fuel injection system. This will serve to inform readers of the D4-S injection system and its use in the FRS/BRZ as well as an over view of the direct injection systems as a whole, the advantages of its use and the difference between both direct injection and port injection. But first some definitions! D4-S: direct injection, four cylinder, superior Direct injection: the act of adding fuel into the cylinder after the valve Port injection: the act of adding fuel into the cylinder before the valve Particulate: when fuel is burned in a low oxygen environment Pre-ignition: Also known as pinging or knocking, occurs when the cylinder pressure peaks before TDC Let's begin, direct injection systems have been around for many year in diesel engines recently have begun to appear in gasoline/Otto cycle engine like those found in most modern cars. Direct injection works by placing a fuel injector directly in the cylinder hence the name direct injection, when the computer gives the command to the injector to fire, the injector opens and releases the fuel which is kept at extremely high pressure (usually several 100 bars) into the cylinder all of this can occur with the valve open or closed allowing the computer to control exactly how much fuel is in the cylinder during ignition. An added benefit of a direct injection only situation is the fact that since there is no fuel in the combustion chambers the possibility of pre-ignition/knock is completely eliminated, again allowing the ECU to have more control of the engine as a whole. Port injection fuel delivery is the most common style used in automobiles today. In a port injection situation fuel is added before air entire the combustion chamber, which means after the valve has closed no more fuel can be added. In this situation the fuel and air molecules mix together better and provide a better mixture and providing better and more constant A/F ratios. Both of these systems offer have positives and negatives but when you combine both systems together the drawbacks of one complement the strength of the other making a more solid well rounded system.