2023 Mercedes-AMG SL43 gets F1-derived turbocharger technology

As manufacturers continue their trend toward using less and less gasoline, engines are getting smaller and turbocharged to make up for the lack of displacement, as we see with the great moth 2022 Mercedes-AMG CLA45. But the turbines suffer from the Catch-22; Want to run better at lower rpm? You’ll need a smaller turbocharger that can spin faster – but that sacrifices absolute power at higher rpm. Or go hard with the turbo, make massive power high, and experience extremely low rpm or post-throttle response. Superchargers and exhaust-based anti-lag systems can deal with these issues, with their own trade-offs. Mercedes-AMG has chosen the number three door for its new SL43 model.

As you can see, AMG borrowed electric turbocharging technology from the Petronas F1 car, combining it with a 48-volt mild-hybrid electric system powered by an alternator on the belt drive attachments and installing it on the new Mercedes-AMG SL43 four-cylinder SL43. alternative. An electronic turbo like this effectively separates the turbo compressor’s capabilities from the exhaust gas speeds while allowing for better control of the unit’s output, so that lag can be reduced at lower speeds without sacrificing significant power at higher engine speeds. It applies to taking Formula 1 technology out onto the street as much as you can get, and in the car that Mercedes associates with the “entry-model” for “tech-savvy buyers” of the AMG SL family, which at launch here in America will only include the SL55 and SL63 eight-cylinder.

A first for AMG, but not *the first*

Technically, this isn’t the first electrically driven turbocharger sold in a production vehicle. This honor belongs to Audi for its 2017 SQ7 and TDi V-8 tri-turbo. However, there is one distinction that AMG can promote over Audi: the AMG turbocharger is driven by the exhaust. And the electric motor. Audi was electric, mounted on the cold side of the engine, and was limited to “only” 70,000 rpm.

The 1.6-inch electric motor of the SL43 turbocharger is attached to the shaft that drives the compressor wheel by a turbine wheel. The AMG e-turbo can handle the heat from the exhaust, as it shares the cooling circuit with the 2.0-liter M139 I-4. Keep in mind that the electric motor and associated electronics are cooled. It can also handle the insane speed a turbocharger needs to boost power, as the tiny engine spins up to 170,000 rpm while exposing it to a 48-volt system shared by the mild-hybrid RSG belt-driven alternator starter unit.

Why bother electrifying a turbo?

The main points of the e-turbo are allowing the 2.0-liter engine to generate power from idle to its red streak with minimal turbo lag. It definitely makes good numbers: 381 horsepower and 354 pound-feet of torque. That’s a lot less than the SL55’s 469 hp and 516 lb-ft of torque (not to mention 577 hp and 590 lb-ft), but not bad for half as many cylinders.

And check the engine’s power curve: 354 lb-ft of peak torque starts at 3250 rpm and continues until 5,000 rpm as it starts lower. This is the diesel-like torque performance of a gasoline engine. GM’s 2.0-liter LSQ I-4 turbo diesel engine makes 281 lb-ft from 1,500 to 2,750 rpm. Although not low in the rev range, the M139’s peak torque range of 1,750 rpm is actually better than the 1,250 rpm range of the LSQ’s peak development.

It’s not far from the SQ7 TDI’s 2,000-rpm torque range, but the tri-turbo diesel delivers about 310 pound-feet of torque thanks to being half the size in both cylinder number and displacement as well as two-thirds less than the turbo. However, the gasoline engine also has a slightly higher horsepower advantage over an equal-volume diesel. The horsepower curve peaks at 381 bhp at 6750 rpm for the SL43’s M139 where the GM LSQ is 128 bhp at 3500 rpm.

While there are exhaust-based anti-lag systems and the supercharger provides low rpm and torque gains, they each come with trade-offs that give the more complex electronic turbo an advantage. Anti-lag systems that use exhaust typically pollute more and are tough on the internals of the catalytic converter. The supercharger requires power from the engine to push air into it for boost, reducing some of the power in the process.

If the supercharger were to draw power, wouldn’t the RSG do that too?

Now, before you argue that recharging a 48-volt system requires the MGU on the motor to drain some power through the drive pulley, consider: MGU only provides a load on the motor when you’re recharging the lithium-ion battery or powering it for the 12-volt system. Other than those times and when the engine starts up or gives it 14 horsepower (yes, the RSG is a power additive too), it trips. This has been running 12v alternators for a long time, with the alternator only being active and drawing engine power when needed, and freewheeling when it isn’t.

Another innovative part of the RSG, though, is something Mercedes has included in its light hybrid cars. While in “Eco” mode, the car can enter “Slide mode”. By using the RSG belt-driven MGU as the motor so the vehicle can maintain speed while saving gas. When you’re at cruising speed and your foot is off the throttle, the RSG will turn the engine off while maintaining drive by shifting the MGU to traction engine mode, driving the crankshaft driving the transmission’s input shaft. This means SL43 owners will potentially save fuel by shutting down the engine in low or no load situations. And there we were concerned that SL43 customers might be affected by higher gas prices…

Clicking off gears

Another feature of the SL 43 is the transmission. While the conventional M139 has always been in the transverse layouts of the power train and conventional automatic transmission, this is the first time it has been used in a longitudinal layout; All SLs are rear wheel drive. It will also be the first time the M139 AMG Speedshift MCT 9G, a Mercedes 9G-Tronic nine-speed automatic transmission that uses a wet-plate clutch over a conventional torque converter, has been used.

This MCT 9G gives better throttle response as the heavy-duty torque converter increases the inertia required to drive it, while the transmission itself has shorter shift times and quicker downshifts via those electronically actuated clutches. It also enables AMG to include a “Race Start” launch control function, which allows the SL43 to sprint at 62 mph from a stop in just 4.9 seconds.

Light weight, high rigidity, great aerodynamics

Since all SLs ditched their metal folding roofs in the 2022 redesign, the SL43 also gets a fabric roof, just like the V-8 models. We’re not complaining, because the move reduced the SL line by 46 pounds. In fact, the wider use of aluminum, magnesium, composites and steel makes the SL43 just under 4,000 pounds. Even when the body weighed only 595 pounds, its torsional stiffness increased by 18 percent. Transverse stiffness is increased by 50 percent over the GT Roadster and longitudinal stiffness is increased by 40 percent over the previous model. In short, the AMG Roadster will be very planted.

The body is not only more solid, but also has many aerodynamic tricks. The first is the active air control system AMG calls “Airpanel”, which uses horizontal air vents behind the grille. Only when certain components reach a certain temperature do these vents open to allow air to pass through. The SL43 also features an active, retractable rear spoiler and optional aerodynamic parts like a larger rear diffuser, larger “slots” on the front and rear fenders, and aerodynamically-improved (and lightweight) 20- and 21-inch-diameter aluminum wheels. The 20-inch wheels also feature plastic air rings for further aerodynamic improvement and reduced weight compared to the alloy version.

This all looks so good, when can I get one

Yes, about US availability.. “Please note that the Mercedes-AMG SL43 is currently still being considered in the US market,” Mercedes tells us. For now, we only get the SL55 and SL63, which are due to hit our shores and dealers “in late spring.” However, with the CAFE standard for a fleet of 49 mpg dropping from NHTSA and starting with an eight percent increase as early as 2024, now might be a good time for Mercedes to consider bringing the SL43 to our shores.