Originally Posted by martinbo

Nope, direct injection doesn't supercede multi-valve heads; rather it complements existing multi-valve efficiency. What direct injection does is get a finer mist of fuel closer to the point of ignition. The finer the mist (or level of stratification), the more droplets of fuel you get, the greater the surface area of fuel to be ignited. This gives a much quicker and more efficient combustion process. Very clever advances in Piezo crystal technology now allows for an oscillating crystal to spray the fuel mist in a cone shaped pattern over the piston in multiple bursts per ignition cycle. Amazing. So, the injectors get the fuel into the combustion chamber, the inlet valves introduce the air and the exhaust valves discharge the burnt gasses.

Multi-valve engines are here to stay for the foreseeable future - it's the actuation of those valves that's destined to change significantly over the next few years. Solenoid controlled electronic valve actuation must be on the cards for production cars soon...

4 Valve heads have many advantages over 5 valve heads notwithstanding the aforementioned freeing up of space for the direct injector. The most significant of which is the lessening of complexity and engineering costs associated with the 5 valve head.