2023 Mercedes-AMG SL43 gets F1-derived turbocharger tech

As automakers continue their trend of using less and less gasoline, engines are getting smaller and turbocharged to compensate for the lack of displacement, as we see with the mighty 2022 Mercedes-AMG CLA45. a kind of Catch-22; do you want it to perform better at low revs? You’re going to want a smaller turbocharger that can spin faster, but sacrifices ultimate horsepower at higher rpm. Or go big with the turbo, crank the power high and suffer abysmal response at low revs or after acceleration. Compressors and exhaust-based anti-lag systems can solve these problems, with their own trade-offs. Mercedes-AMG has chosen door number three with its new SL43 roadster.

You see, AMG borrowed electric turbocharging technology from the Petronas F1 car, combining it with a 48-volt mild-hybrid electric system powered by a generator on the accessory drive belt and slapping it on the new SL43 at four-cylinder from the Mercedes-AMG SL 2023 a variant. An e-turbo like this effectively disconnects the turbo’s compressor capabilities from exhaust gas velocities while allowing more precise control of unit output, so lag can be reduced at lower speeds without sacrificing great power at higher engine speeds. It’s as true as it gets of a transfer of Formula 1 tech to the street, and in a vehicle that Mercedes considers the “entry-level model” for “tech-savvy buyers” of the AMG SL family. , which at launch here in America will only feature the SL55 and SL63 eight-cylinder.

A first for AMG, but not *the* first

Technically speaking, this is not the first electric turbocharger ever sold on a production vehicle. This honor goes to Audi for its 2017 SQ7 and its triple-turbo V8 TDi. However, there is one distinction AMG can brag about Audi: AMG’s turbocharger is both exhaust-driven and the electric motor. The Audi was electrically powered, mounted on the cold side of the engine and was limited to “only” 70,000 rpm.

The SL43 turbocharger’s 1.6-inch-thick electric motor is connected to the shaft that drives the compressor wheel through the turbine wheel. The AMG e-turbo can handle the heat from the exhaust, as it shares a cooling circuit with the 2.0-liter M139 I-4. Consider the electric motor and its associated electronics cooled. It can also handle the insane speed the turbocharger needs to accelerate, as the little motor spins up to 170,000 rpm while being powered by the 48-volt system shared by the belt-driven motor-starter unit Mild hybrid RSG.

Why bother electrifying a turbo?

The key points of the e-turbo are to allow the 2.0-liter engine to produce power from idle to its redline with minimal turbo lag. It certainly does some good numbers: 389 horsepower and 354 lb-ft of torque. That’s well below the SL55’s 469 hp and 516 lb-ft of torque (not to mention the SL63’s 577 hp and 590 lb-ft), but not bad for half the cylinder count.

And look at the engine’s power curve: the 354 lb-ft of torque peak starts at 3,250 rpm and lasts until 5,000 rpm where it just begins to drop off. This is the diesel-like torque performance of a gasoline engine; GM’s 2.0-liter LSQ turbodiesel inline-4 produces 281 lb-ft from 1,500 to 2,750 rpm. While not as low in the rev range, the M139’s 1750 rpm peak torque range is actually better than the LSQ’s peak torque 1250 rpm range.

That’s not far off the SQ7 TDI’s 2,000 rpm torque range, but the triple-turbo diesel produces around 310 lb-ft less torque thanks to half the size of the cylinder count and the displacement as well as two-thirds less turbos. That being said, a petrol engine also has a small power advantage over an equally sized diesel. The power curve peaks at 381 hp at 6,750 rpm for the SL43’s M139 where the GM LSQ produces a paltry 128 hp at 3,500 rpm.

While there are exhaust-based anti-lag systems and superchargers that offer low-end horsepower and torque gains, each comes with a trade-off that gives the more complex e-turbo an edge. Anti-lag systems that use the exhaust generally pollute more and are hard on the internal components of the catalytic converter. A supercharger requires power from the engine to inject air into it to boost it, sapping some power.

If a compressor consumes energy, wouldn’t RSG do it too?

Now, before saying that recharging the 48 volt system requires the motor MGU to draw power through the drive pulley, keep this in mind: the MGU only introduces load to the motor when it is recharging this lithium-ion battery or it supplies power for the 12 volt system. Outside of those times and when it starts the engine or gives it a 14hp boost (yes, the RSG is also a power-adding device), it’s decoupled. This has long been an operation of 12 volt alternators, where the alternator is only active and draws power from the engine only when needed, and coasts when not .

However, there is another innovative part of the RSG and it’s something that Mercedes has included in its mild hybrids. In “Eco” mode, the car can enter “gliding mode”. By using the RSG’s belt-driven MGU as the engine, the car can maintain speed while saving fuel. When you are at cruising speed and your foot is not on the throttle, the RSG system will shut off the engine but maintain drive by switching the MGU to traction engine mode, driving the crankshaft which drives the shaft transmission input. This means that SL43 owners will potentially save fuel by shutting down the engine in low to no load situations. And there, we feared that SL43 customers would be pinched by high gas prices…

By clicking on the gears

Another advantage of the SL 43 is its transmission. While the traditional M139 has always been in transverse powertrain configurations and traditional automatic transmissions, this is the first time it has been used in a longitudinal configuration; all SLs are rear-wheel drive. It will also be the first time the M139 will use the AMG Speedshift MCT 9G, which is a Mercedes 9G-Tronic nine-speed automatic transmission that uses a wet-disc clutch over the traditional torque converter.

This gives the MCT 9G better throttle response as the heavy torque converter increases the inertia needed to drive it, while the transmission itself benefits from shorter shift times and quicker downshifts via these electronically controlled clutches. It also allows AMG to include a “Race Start” launch control feature, which allows the SL43 to sprint to 62 mph from a standstill in just 4.9 seconds.

Low weight, high rigidity, superb aerodynamics

Since all SLs ditched their metal folding hardtops in the 2022 redesign, the SL43 also gets a fabric roof, just like the V-8 models. We’re not complaining, as the move slashed the SL line by 46 pounds. In fact, the use of aluminum, magnesium, composites and steel more broadly keeps the SL43 at just under 4,000 lbs. Even though the body weighs only 595 pounds, its torsional rigidity is up 18%. Transverse stiffness is up 50% over the GT Roadster and longitudinal stiffness is up 40% over the outgoing model. In short, it will be a very planted AMG roadster.

The body is not only more rigid, but also has many aerodynamic tricks. The first is the Active Air Control System that AMG calls “Airpanel”, which uses horizontal louvers behind the grille. It is only when certain components have reached a certain temperature that these flaps open to allow air to pass through. The SL43 also includes an active, retractable rear spoiler and optional aerodynamic parts such as a larger rear diffuser, larger “cops” on the front and rear bumpers and aerodynamically optimized (and lightweight) aluminum wheels 20 and 21 inches in diameter. The 20-inch wheels also feature plastic aero rings for an additional aerodynamic improvement and weight reduction over a metal version.

This all sounds good, when can I get one

Yes, about US availability. “Please note that the Mercedes-AMG SL43 is currently still under consideration for the US market,” Mercedes tells us. So far, we’re only getting the SL55 and SL63, which should hit our shores and dealers “in late spring.” However, with a new fleet CAFE standard of 49mpg coming from NHTSA and starting with an 8% increase as early as 2024, now might be the time for Mercedes to consider bringing the SL43 to our shores.