Mitsubishi Motors Corporation (MMC) has announced a new engine. The ‘4J10’ is a lightweight and compact 1.8-litre petrol engine incorporating a new version of the company’s MIVEC variable valve timing system and the latest version of Auto Stop & Go (AS&G) tech.

The new 4J10 engine/AS&G combination will power the Japan-market RVR (ASX to us), Galant Fortis sedan (Lancer) and Galant Fortis Sportback (Lancer Sportback). MMC says that with the 4J10, the three models show 12% improved fuel efficiency in the Japanese 10-15 mode.

MMC says that the new MIVEC system together with improved combustion stability and reduction in piston friction provide better economy without any loss in engine performance over the existing 4B10 MIVEC engine. Used in overseas Lancers and the Proton Inspira 1.8, the 4B10 is a 1.8-litre, inline-4, 16-valve engine. It has DOHC instead of the new engine’s SOHC. Compared to the 4B10, the new 4J10 has just 1kW and 5 Nm less, so it’s a good trade for the 12% better economy.

MMC first applied MIVEC in 1992, and there have been two types so far – in one, the system switches between different valve lifts and valve opening durations according to engine speed, while in the other (as in the 4B10) the system varies the valve opening timing on a continuous basis.

The new MIVEC system in the 4J10 can do what the previous two systems could do “but at the same time, all the time”. This is thanks to a single mechanism that mechanically couples intake valve lift, opening duration and timing, allowing all three parameters to be varied simultaneously and continuously. The result is ideal valve operation control and the reduction of pumping losses.

AS&G is nothing new for MMC – it’s already being used in manual cars for Europe – but this latest version has been tailored for cars running continuously variable transmissions (CVT). The addition of a new control unit means that the new AS&G is integrally controlled along with the engine, CVT, Active Stability Control (ASC) and climate control.

Other changes include the use of a more durable 12V battery and a DC/DC converter. These are to prevent breaks in audio sound and to prevent the sat nav from rebooting when the engine restarts.

These developments are part of the Mitsubishi Motors Environment Initiative Program 2015, which targets 25% reduction in on-road CO2 emission of new vehicles compared to the 2005 global weighted average.