In the absence of BMW's M division tuning the Z4 into a meaner model, the aftermarket is stepping up to the challenge. For example, G-Power is able to push the roadster's output to 494 horsepower (368 kilowatts) from a 3.0-liter turbocharged inline-six engine, versus 335 hp (250 kW) for the European-spec M40i grade or 382 hp (285 kW) for this version in America. Torque grows to 516 pound-feet (700 Newton-meters), instead of 369 pound-feet (500 Nm) in stock form in both Europe and the U.S.
G-Power claims that the tuned Z4 can hit 62 miles per hour (100 kilometers per hour) in 3.9 seconds, versus 4.5 seconds in the factory trim. The firm estimates the roadster can hit over 186 miles per hour (300 kilometers per hour), rather than the electronically limited 155 mph (250 kph) off the showroom floor.
The upgrades that allow for these improvements include G-Power's Performance Software V3 for €1,639 ($1,851 at current exchange rates) that remaps the engine control unit. The top speed increase adds €500 ($565). A modified turbo goes for €2,899 ($3,275), and an upgraded intercooler with better cooling ability costs €1,471 ($1,662). For better breathing, there are flow-optimized downpipes with sports catalytic converters for €1,639 ($1,851).
G-Power's results are fairly impressive since the tuner's Swiss competitors at Dähler can't make the car quite as potent. For example, the firm's stage 1 kit takes the Z4 to 402 hp (300 kW) and 457 lb-ft (620 Nm), and the stage 2 version takes the output to 435 hp (324 kW) and 472 lb-ft (640 Nm).
G-Power largely focuses on upgrading the Z4's performance, but the company can also tweak the roadster's look with a set of 20-inch wheels with five pairs of dual spokes. They measure 9 inches wide in the front and 10.5 inches at the rear. A set of them goes for €6,681 ($7,545).
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