The extra power comes from a combination of new turbos, modified software, reshaped exhaust ports, and a different compression ratio. Max boost is 19.6 psi versus 17.4. Engine response is improved through a dual-mass flywheel that's 1.5 pounds lighter than the one in the GT S's engine.
The AMG Speedshift DCT seven-speed transmission was modified for the R with a taller first gear and shorter ratios for seventh and the final-drive. Transmission cooling also got an upgrade.
The dynamic engine and transmission mounts from the other AMG GTs carry over. To get the power from the engine to the transaxle, the GT R uses a 30-pound carbon-fiber torque tube that is about 40 percent lighter than the aluminum piece used on the regular GT. The R takes a claimed 3.5 seconds to hit 60 mph, two tenths quicker than AMG claims for the GT S