The upgrades take the 3.0-litre turbocharged inline six from 224kW and 440Nm to 242kW and 480Nm.
The US-spec T6 engine will eclipse the 4.4-litre V8 in the XC90, which produces 232kW and 440Nm.
But there are currently no plans to sell the 242kW T6 outside North America, with Volvo Car Australia’s Jaedene Hudson confirming the engine has been tuned specifically for that market.
“In terms of power, they’ve done that in the US … it’s not direct from the factory in Sweden,” Ms Hudson said.“There are no plans at this stage to change the R-Design range in Australia.”
The Australian T6 R-Design range is powered by the standard 224kW/440Nm tune of the engine and currently includes the S60 sedan, XC60 compact SUV and the V60 wagon. The V60 is not sold in the North America, and as such there is no 242kW V60 available.
Volvo Cars North America President and CEO, Doug Speck, said the enhanced S60 and XC60 models will offer improved performance and renewed driving enjoyment.
"The jump in performance will re-define these two R-Design models," Mr Speck said."Along with styling and suspension features that set them apart from other versions, our two newest R-Design models will have a higher 'fun-to-drive' quotient. I see that as a positive thing, and so will car buyers."
Volvo says peak torque from the tweaked T6 comes on at 3000rpm and remains available throughout the rev range. The standard T6 delivers maximum torque from a considerably lower 2100rpm and maintains it up to 4200rpm.
Prices for the new models will start at $US42,275 ($38,980) for the S60 T6 R-Design and $US43,150 ($39,790) for the XC60 T6 R-Design.
In Australia, the S60 T6 R-Design starts at $69,150 while the XC60 T6 R-Design is priced from $70,150.