Your first reaction here might be to wonder exactly what you’re looking at here. You know it’s a piston from Wiseco, of course, but you’ve probably never seen a dome shape quite like this, and you definitely won’t be able to guess the application. We won’t keep you in suspense, though - this is their new domed piston for the Mazdaspeed3. That, of course, brings up a whole new question; namely, why do we even care about a piston for a turbocharged import?
The answer to that question lies in the fact that it’s a direct-injection engine, where fuel is sprayed directly into the combustion chamber, much as it is in a diesel engine. If you’ve been paying attention to Ford’s new Coyote 5.0L, you may also be aware that the head castings for that engine already include a curious bump in the combustion chamber that is the telltale sign of a future switch to direct injection. That means that the same technology seen on this Mazda piston will directly relate to the DI Coyote, when it finally hits a year or two down the line.
The stock piston is a flat-top design, but the “smiley face” shape seen in Wiseco’s slug has a specific purpose - giving the DI injector a “catcher’s mitt” (the face’s nose) to improve distribution, and the milled-out “mouth” controls compression ratio by virtue of total chamber volume. Through careful engineering, Wiseco can extend the crank angle range for the injection event, and avoid cylinder wall wash-down as well.
So now you know why you should be concerned about an import four-banger piston; DI for the Mustang is coming, and Wiseco is already prepared to do some interesting things with it.