The Present & Future of GDI

An advanced look at direct injection on the Gen V LT1 and LT4 V-8s.

- Scott Parker and Howard Tanner

By now, no doubt, you have come to realize that direct injection (DI) is not the performance-killer it was once thought to be. There is a literal race to see who can make the most power with the new Gen V DI engine, and so far we are all winning. In the race to the top, there is most certainly a cap on horsepower that can be hit with even the more stout LT4 fuel system. As a result, some have used methanol injection nozzles, throttle body gasoline injection, and even a separate port fuel-injection system. But before we add fuel sources or abandon direct injection all together, it is important to understand just what is going on under the hood of our C7 Corvette or sixth-gen Camaro SS.

Assuming you have gotten past the concept that fuel is now shot directly into the combustion chamber, let’s talk about what happens next. The chamber on a Gen V engine has been designed with over a million man-hours of effort. Yes, a million. Much of it is done through CFD (computational fluid dynamics) and lots of engine dyno time. As with any engine, the intake valve opens to allow air to enter this chamber. The air does not always come in smoothly. In fact, it comes in as a tumble, swirl, and axially. In port-fuel injection this was very helpful in creating a homogenous mix, something we will revisit shortly. In DI, it’s raw, fresh air that enters the chamber. This is also referred to as “charge motion.” The fuel injector has six small discharge orifices that are strategically aimed at various parts of the chamber. This is where the engineering comes in. It is critical that every droplet of fuel can bond with the incoming oxygen and that it mixes evenly, or homogenously. The timing of when and where the fuel is injected is easier said than done—especially when we start modifying it!