Japan's Mazda Motor Corp said on Tuesday it had developed an advanced stop-and-go system, diesel engine and other technologies aimed at boosting its cars' average mileage by 30 per cent in seven years.

With little added cost, Mazda's new stop-and-go feature boosts fuel efficiency by around 10 per cent in urban areas, where cars stop frequently at traffic lights, Mazda said.

The system is the first in the world to control the position of the pistons when the engine stops automatically during idling, which Mazda said enables a quick and quiet start by directly injecting fuel into the cylinder in the optimal position.

The technology enables a virtually seamless restart of the engine in 0.35 second, or about half the time that existing systems take, Mazda said. It will be introduced in cars in Japan and Europe next year.

Mazda, owned one-third by Ford Motor Co, also announced a new, more powerful 2.2-litre diesel engine to replace the current 2.0-litre diesel engine it mounts on the Mazda3, Mazda5 and Mazda6 models in Europe.

Managing Executive Officer Nobuhiro Hayama said the bigger engine held carbon dioxide emissions and fuel efficiency at the same level as the 2.0-litre engine, but would enable Mazda to power larger cars, thus lowering its fleet's overall emissions.

The new engine will be introduced in Europe from 2009.

To reach its fuel economy goal for 2015, Mazda will also start replacing resin-based parts on its new models, beginning in a few years, with lighter material to reduce vehicle weight.

Announcing the new plastic molding technology on Tuesday, Mazda said the technique would slash consumption of plastic resins by 20 to 30 per cent, also helping to cut costs.