Mercedes-AMG SL43 Has a 389-HP Turbo-Four with F1 Tech

• The Mercedes-AMG SL43 is an entry-level model for the latest generation of the SL. It is powered by a 389-horsepower turbocharged inline-four.
• This is the first production vehicle to feature a turbo with an electric motor on the turbocharger shaft that can spin the compressor wheel to reduce lag and maintain boost pressure when the driver lets off the gas pedal.
• Mercedes is still deciding whether it wants to bring the four-cylinder SL43 to the United States market.

The new Mercedes-AMG SL43 may be the entry-level model in the grand tourer’s lineup, but that doesn’t mean the SL43 is basic. While it has only half as many cylinders as its higher-performance, V-8-powered SL55 and SL63 siblings, this model has technology derived from Formula 1 that promises increased responsiveness from the turbocharged inline-four.

The SL43’s party piece is a turbocharger with an electric motor plus the typical exhaust-gas plumbing. This production-car first is fitted to the M139 2.0-liter inline-four, the same engine found in the CLA45 and GLA45 AMG models. The motor is only about an inch and a half thick and mounted on the shaft between the turbine wheel and compressor wheel. The whole point is that this motor can spin the compressor wheel before the exhaust gases do, reducing turbo lag, providing a near-immediate response when the driver pins the throttle, and maintaining boost pressure even when the driver lets off the gas or hits the brakes. This same technology is found in the turbocharged 1.6-liter V-6 hybrids used by the Mercedes-AMG Formula 1 team.

The four-cylinder engine pumps out a continuous total of 376 horsepower and 354 pound-feet of torque, while the 48-volt, belt-driven starter-generator can provide a brief boost of 13 extra horses. The 48-volt setup also allows the SL43 to recoup energy while slowing and smoothing out the engine’s start-stop function. The M139 is, for the first time, mounted longitudinally in the SL43 and linked to a nine-speed automatic transmission with the AMG-typical wet clutch pack in place of a torque converter. Mercedes claims the rear-wheel-drive roadster can hit 62 mph in 4.9 seconds on its way to a 170 mph top speed.

A few minor visual changes distinguish the SL43 from the 55 and 63. The tailpipes are round and the rear bumper is simplified, ditching the vents behind the rear wheels. The front bumper is also reshaped, and the SL43 rides on 19-inch wheels as standard, with optional 20- and 21-inch wheels. The SL43 isn’t confirmed for the United States, with a Mercedes spokesperson telling Car and Driver that the roadster is “is currently still under consideration for the U.S. market.” If it does reach our shores, expect it to be considerably cheaper than the SL55, which we estimate will cost around $135,000.