I found this article about upcoming changes to the Mercedes-Benz AMG line, they will be going to twin turbo chargers on the 5.5 liter V8 as opposed to using the naturally aspirated 6.2 liter as in the “AMG 63″ cars.

This article was written by Greg Kable over on the Autoweek website as part of their coverage of the Geneva Auto Show. I’ve had a subscription to Autoweek for about 12 years now, I’d highly reccomend it if you’re looking for industry insider information and news as opposed to a magazine just full of reviews and road tests. Autoweek realy does a great job.

Mercedes-Benz’s AMG division has taken the wraps off a new four-valves-per-cylinder, twin-turbocharged, 5.5-liter direct-injection V8 gasoline engine destined to appear in all its various performance models as a replacement for today’s naturally aspirated 6.2-liter V8.

Code-named M157, the new 90-degree unit is based around Mercedes-Benz’s upcoming twin-turbocharged 4.6-liter V8–the M278 as it’s known internally–with a stiffened aluminum block, 98-millimeter-by-90.5-millimeter bore and stroke measurements, 106-millimeter cylinder bore spacing, wet-sump lubrication and total weight–including its dual Garret-Honeywell turbocharger installation–of 450 pounds.

Two distinct versions of the new AMG engine are planned for North America. In standard guise, AMG’s new 5.5-liter V8 delivers 544 hp at 5,500 rpm and 590 lb-ft of torque between 2,000 rpm and 4,500 rpm–an increase of 19 hp and 125 lb-ft over the existing 6.2-liter V8.

As part of a so-called performance package to be made available on selected models, AMG also developed a more highly tuned version kicking out 571 hp at 5,500 rpm and a whopping 664 lb-ft of torque from 2,500 rpm to 3,750 rpm.

Both engines rev to a maximum of 6,300 rpm.

The first AMG model to receive the new engine will be a reworked version of the S63 AMG set to reach North America this summer, running the same seven-speed MCT gearbox as that found in the E63 AMG.

No performance claims for the new car, which will be previewed at the Geneva motor show by a lightly veiled concept car decked out in the colors of the company’s legendary 300 SEL 6.8 AMG race car, but AMG does claim a 25 percent reduction in fuel consumption over the existing S63 AMG with a estimated 23.5 mpg, achieved, in part, by the inclusion of a driver-selectable Controlled Efficiency program. Among other functions, it remaps the gearbox for more economical shift points, including a launch-off mode that sees it select second gear.

Other fuel-saving technology to be included on the new car is the Intelligent Generator Management System seen on the E63 AMG. It uses an alternator which converts kinetic energy created during coasting and braking into electricity and stows it in the battery. The gearbox was also reworked to incorporate a new automatic stop/start system.

According to AMG boss Volker Mornhinweg, the fuel-saving measures included on the S63 AMG will allow it to sneak in under the threshold for the U.S. gas-guzzler tax.

Despite the drop in capacity with the new powerplant, Mercedes-Benz’s fast-car offshoot has decided to retain the 63 nomenclature that graces all of its existing models, save for the SLK55 AMG. Speculation had been mounting in recent months that it may readopt the old 55 name. But with more power and torque, AMG ultimately decided the new engine should be, somewhat confusingly, marketed under today’s nameplate.