The BMW X3 gets a twin-scroll turbo 2.0-L four-cylinder diesel engine for the U.S. market for the 2015 model year, based on an engine that was introduced in Europe in 2010. However, the engine now meets U.S. Clean Diesel emissions standards, and the SUV is fitted with a package of acoustic panels that actually makes it somewhat quieter than competitive gasoline engines.

The optional diesel develops 180 hp (134 kW), but with 280 lb·ft (380 N·m) of low-end torque, it's a more-than-acceptable performer off the line, rated at under 8 s for 0-60 mph (0-97 km/h).

The standard engine is a twin-scroll turbo 2.0-L I4 gasoline engine rated at 240 hp (180 kW) and 260 lb·ft (352 N·m). Also available is the 3.0-L inline gasoline six rated at 300 hp (224 kW) and 300 lb·ft (407 N·m) to round out the engine lineup. The automatic transmission is an eight-speed unit.

Aggressive look to front end

The front end was restyled to give the car a more aggressive look, a "strong but silent" demeanor reinforced by the comprehensive insulation package. The refreshed model is being introduced at the 2014 New York International Auto Show this week.

With the doors closed, the diesel engine-equipped interior is amazingly quiet, rated at just 69 dB (at idle) in BMW wind tunnel tests, according to Niklas Fichtmueller, Project Leader for X3/X4 models. This is about 2 dB lower than competitive premium cars, he said. Some of that comes from insulation stuffed into body cavities, even the small channels around the B-pillar reinforcement.

Interestingly, BMW made no changes to diesel calibrations to reduce NVH, Fichtmueller said. He explained that the engine was tuned for performance and fuel economy, and to incorporate Clean Diesel emissions hardware including SCR (selective catalytic reduction) for oxides of nitrogen (NOx) control. Although the engine itself was built to minimize noise, the piezo-electric injectors required a "very hard" pulse as part of the fuel economy tune, and that is not silent. Yet, even with the doors open and the engine running, the diesel's clatter noise level was relatively low.

Comprehensive noise abatement

BMW took a comprehensive approach to the noise challenge, going beyond the engine itself. Although the engine cover was not the thick "pillow" we have seen on other diesels, there are acoustic covers in places they haven't been seen before, as part of an effort to also control wind noise.

One pad is at the front of the engine, another wraps around the oil pan. There is new padding for the cowl area that not only absorbs noise but better blocks its transmission. The sides of the engine compartment also have strategically located insulation patches.

The holes through which the front axle shafts of the X-drive all-wheel-drive system pass are reduced to an engineering-acceptable minimum to lower noise transmission, including that of wind, and the wheelhouse insulation panels are extended to cover what previously had been open areas.

The vehicle's rear was found to be a source of noise transmission, and acoustic panels not only were installed in the C-pillar, but also against the inside surface of the hatch.