Subaru’s Turbocharged Diesel Boxer Engine

Diesel Subaru Outback

A bit of a latecomer to the party, Subaru’s first diesel and the first ever boxer turbodiesel in a car may soon make it’s way across the pond.  Right now, potential U.S. buyers must wait with envy as the Europeans enjoy Subaru’s boxer turbodiesel.  But don’t worry it should be coming.

1st Passenger Car Boxer Diesel Engine

Of primary importance to people looking to buy a diesel engine in a passenger car is gas mileage.  With mileage close to 50 mpg, the boxer diesel would have to be regarded as a success in that area.  The 2.0-liter DOHC horizontally opposed flat-four common-rail diesel produces 148 hp and 258 pound-feet of torque at only 1800 rpm! The gasoline version of Subaru’s 2.0-liter four-cylinder boxer also manages 148 hp, but just 144 lb-ft of torque.  So it’s a win-win on that front.  The boxer-configuration was both an asset to performance and a bit of a challenge in the engine’s development. Kenichi Yamamoto, who was in charge of it’s progress, says that Subaru moved the variable-nozzle turbocharger to the bottom of the engine to improve emissions and helps keep the center of gravity low. To minimize weight, the block as well as the cylinder heads are made from aluminum. The intercooler is still on top of the engine near the intake manifold, with longish hoses connecting the turbo to the intercooler-yes, the hood scoop is functional. Emissions are handled by an EGR system, particulate filter, and an oxidation catalytic converter, making the engine compliant with European regulations.  Some changes were made to accommodate the new powerplant, including the use of liquid-filled engine mounts, modified spring rates, larger CV joints, electric power steering, and larger front disc brakes.A new five-speed manual transmission, geared specifically for diesel engines was mated to the engine.

Diesel is a snug fit in the engine bay

Following the engine’s use in 2008 Subaru Legacy and Outback models, the Impreza will get the diesel towards the end of the year.  The biggest hurdle in the engine being used in the States are California’s strict emission’s laws.  Subaru estimates that the addition of the the particulate filter needed to make the engine fully compliant would add around $1,500 to the price of the car.  Subaru is committed to only bringing its diesel to the States if they can be available in all 50 states.  At the risk of getting anyone’s hopes up, Subaru’s confidence in the new engine has led to speculation that it can produce versions with as much as 161 hp without any risk to its durability.  Could a WRX or STi be in the future plans?

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