The M273 and M156 V8's
The new V8 is the M273. The M273 features dual-overhead camshafts, four valves per cylinder, a two-stage magnesium intake manifold, and variable valve timing on both the intake and the exhaust valves. Couple this with the 7G-Tronic seven-speed automatic, and you have a powertrain that isn't averse to dropping three gears and redefining what you thought fast was. Currently, the M273 comes in two versions; the 4.7 which produces 335 horsepower and 339 pound-feet of torque, and the 5.5-liter with 382-horsepower and 391 pound-feet of torque.
How much of an improvement is the M273 over the M113? Well, the M113 based 4.3 produced 295 foot pounds of torque from 3000-4000 RPM. At 1000 RPM, the M273 based 550 is already producing 293 foot pounds. The two engines really aren?t comparable. The new 550 produces 26% more horsepower and 15% more than the old M113 based 500. In case you?re wondering how an M113 based 5.5 liter stacks up, the normally aspirated M113 based 5.5 liter AMG produced 342 horsepower and 376 pound feet of torque. The M273 has 11% more horsepower.
That?s not to say the M273 is the most powerful engine at Mercedes-Benz. The M156 based AMG 63 is a bit more vigorous. In the CLK, the new AMG 63 surpasses the M273 with 475 horsepower and 465 pound feet of torque. In an E, that same AMG 63 produces 507 horsepower. The M113 based, supercharged 5.5 liter is still available in the SL55AMG. That engine produces 510 horsepower and 531 foot pounds of torque. Some say you can never have enough horsepower. I wonder if they?ve ever driven a car with six hundred ponies. The SL65 produces 604 horsepower and 738 foot pounds of torque. What does 700+ foot pounds of torque feel like? I?ve heard it described as similar to being rear-ended by a Freightliner. I?ll have to take their word for it. You would think that a car that costs $190K and can run eleven-sixties in the quarter mile would be top dog, but we?re not there just yet. At the top of the food chain, we have the SLR McLaren. It?s both a tenth of a tick faster to sixty MPH, and not limited by the SL65?s 155 MPH limiter. With it?s supercharged M113 based 617 horsepower power plant, the SLR is capable of knocking a 208 MPH hole in the atmosphere.
The "best" engine design is a moving target. Fortunately, the engineers at Mercedes Benz are chasing that target.