Turbochargers have gone a long way from when they were first introduced in vehicles. No longer are turbos laggy and only produce power beyond a certain RPM. Thanks to newer technology such as variable-geometry and twin-scroll turbos, turbocharging has become more efficient than ever. So much so, most manufacturers are adopting them for use in lowering emissions and improving performance.
Curiously however, Mazda seems to be experimenting with an older sequential twin-turbo setup as seen in their latest patent. Unlike a standard twin-turbo setup with two turbos spooling simultaneously, a sequential setup uses two differently sized turbos with one turbo spooling up earlier than the other to provide low-end boost. The smaller turbo then also helps spool the larger turbo, which provides boost at higher-rpms.
Unlike older sequential twin-turbo setups, Mazda's patent does show a more compact design, taking up less space. Also both turbos appear to be contained in one unit and shares the same exhaust outlet, allowing for a more simple manifold design.
The more compact design and less piping use allows this application to be used on smaller cars with tighter engine bays. The smaller system also helps keep the weight down and uses less material to be produced. Depending on how it's setup, the system could possibly provide better response and produce more power than a single turbo setup.
Currently, only the SKYACTIV-G 2.5T engine is turbocharged in Mazda's engine line up as the rest are still naturally aspirated. A sequential twin-turbo setup has not been used in any of Mazda's line up since the third-generation FD RX-7 was discontinued back in 2002. As no details have yet to surface, it is still uncertain where this sequential twin-turbo setup would be used. That is if it makes it into production.