In most cases, when a manufacturer makes an engine change, it makes the engine bigger by increasing the size, cylinders or output. In BMW’s case for the 2012 Z4, it's done the exact opposite. For 2012, the base Z4 gets renumbered and receives a smaller engine, shrinking from the previous naturally aspirated 3.0-liter inline-6 engine to a turbocharged 4-cylinder 2.0-liter engine. In doing so, the Z4 loses only a small amount of horsepower (around 15), but gains 40 additional lb-ft of torque, making it a decent trade-off for enthusiasts. For 2012, three trim levels are available for the rear-wheel-drive, 2-passenger BMW Z4: sDrive28i, sDrive35i and sDrive35is. The base sDrive28i trim comes factory equipped with a 240-hp 2.0-liter DOHC 16-valve inline-4 engine with TwinPower Turbo technology, direct injection, and Valvetronic and Double-VANOS steplessly variable valve timing, all married to a 6-speed manual transmission to make 260 lb-ft of torque. The sDrive35i and sDrive35is trims come standard with a 300-hp 3.0-liter DOHC inline 24-valve 6-cylinder engine with aluminum engine block, TwinPower Turbo technology, piezo direct injection and Double-VANOS steplessly variable valve timing. The sDrive35i comes standard with a 6-speed manual transmission and makes 300 lb-ft of torque, while the sDrive35is is equipped with a 7-speed automatic transmission (optional for both the sDrive28i and sDrive35i trims) and makes 332 lb-ft of torque. All Z4 trims run on premium gas. The sDrive28i is estimated by the EPA to get 24 mpg city/33 highway when equipped with a automatic transmission and 22/34 with a manual transmission. The sDrive35i gets 19/26 with an automatic transmission and 17/24 with a standard transmission, and the sDrive35is is estimated at 17/24. Standard equipment for the new sDrive28i trim includes air conditioning with manual climate control and microfilter ventilation, dynamic cruise control, power windows with "one-touch" push-pull open/close for driver, heated dual power external mirrors, electric power steering with Servotronic power assist, a 3-spoke leather-wrapped multifunction sport steering wheel (with controls for the audio system, cruise control and Bluetooth wireless communication), black leatherette upholstery, 6-way manually adjustable seats, an antitheft system, AM/FM/CD audio system with radio data and MP3 capabilities, HD radio with "multicast" FM station reception, an auxiliary audio input adapter for portable music players, iPod and USB adapter, Bluetooth wireless capability, heated glass rear window, retractable hardtop, rain-sensing windshield wipers, Xenon adaptive headlights with auto-leveling, and 17-inch star spoke light aluminum alloy wheels with run-flat performance tires. In addition to a bigger, more powerful engine, moving up to the sDrive35i trim nets the buyer multizone automatic air conditioning with climate control, leather seats, a power passenger seat, and seat memory for both driver’s and passenger’s seats. The sDrive35is also gets 18-inch star spoke light aluminum alloy wheels with run-flat performance tires. Optional equipment available for most, if not all, trims includes a navigation system, heated adjustable driver’s seat with lumbar adjustment, heated adjustable passenger’s seat with lumbar adjustment, an auto-dimming rear-view mirror, rear parking aid and Sirius XM satellite radio with a trial subscription. Many of the available options are collected together in packages, such as the Premium Package, Sport Package and Cold Weather Package. Numerous safety and security features can be found standard on the 2012 BMW Z4, such as a dual-airbag supplementary restraint system, active knee protection, side-impact airbags, a mechanism for disabling the deployment of the front, knee and passenger's-side airbags, rollover protection system, tire pressure monitoring system, daytime running lights, 4-wheel antilock ventilated disc brakes, dynamic stability control (including brake fade compensation, brake drying and brake standby features), dynamic traction control, a crash sensor (which activates battery safety terminal disconnect of the alternator, fuel pump and starter, automatically unlocks doors and turns on hazard and interior lights), antitheft alarm system with remote operation and an interior motion detector, and a central locking system with a double-lock antitheft feature, selective unlocking and interior locking switch. Although most current 2012 BMW Z4 owners notice no drop-off in power, many have mentioned how loud the sDrive28i can be when idling at a stoplight. Otherwise, the Z4 gets high marks for handling and throttle power off the line. Many consumers note how quiet the engine is at highway speeds.