Cummins has released a new QSB6.7 diesel engine with increased power now offered at 550hp for the recreational marine market.

The company says that while meeting the USA’s EPA Tier 3 emissions regulations the QSB6.7 offers better performance and improved sociability and operations over its popular QSB5.9 model, without sacrificing fuel economy.

The EPA Tier 3 emission standards are approximately a 20 per cent reduction in NOx and a 50 per cent reduction in particulate matter compared to Tier 2. The standards are being phased in from January 1 this year through to 2014.

Cummins said its engineers reached Tier 3 levels by improving the efficiency of combustion.

“A new fuel calibration strategy allows for less wasted fuel, creating less particulate matter and resulting in cleaner exhaust. While reducing emission levels often means a sacrifice in performance Cummins is proud to have avoided that sacrifice,” states the company press release.

The QSB6.7 is also said to provide more torque for better acceleration and maintaining speed through turns.

Cummins claims a pair of 480hp QSB5.9 engines linked to Zeus pods installed in a 44-foot express cruiser accelerated the test boat to 17.4kts (20mph) in 14 seconds, while the same boat powered by 480hp QSB6.7s accelerated to that speed in just 8 seconds, with little change to fuel economy.

The QSB6.7 also employs a new fuel calibration strategy for optimal fuel economy at cruising speeds, where the engine is most often used, rather than at wide-open throttle.

“The QSB6.7 is sociably improved, offering exceptionally low cold-start smoke levels, and significant sound reduction at cruise and rated speeds compared to the QSB5.9,” Cummins adds.

Among improvements is an air-filter temperature sensor for engine use in extreme environments, and the standard fuel system made compatible with low-lubricity fuels.

The QSB6.7 is available from 230 to 550hp for inboard and Zeus pod-drive applications. QUICK SPECS

Specifications: Cummins QSB6.7

TYPE In-line six-cyclinder four-stroke diesel

ASPIRATION Turbocharged/aftercooled

RATED HP From 230 to 550


BORE/STROKE 107 x 124mm

FUEL SYSTEM Bosch HPCR (high-pressure common rail)