The 2013 RDX is so much different (and more likeable) than the 2012 model, it wouldn't have come as a surprise had Acura decided to change the name. The 2.3liter turbocharged 4-cylinder has been canned in favor of a (wait for it...) 3.5-liter V6 which offers 33 more horsepower and (wait for it......) much better fuel economy. Go figure. This engine features Honda's VCM technology, which allows the engine to operate in 3-cylinder, 4-cylinder and 6-cylinder modes. Coupled with the new-for-2013 6-speed automatic transmission, this gives the RDX impressive acceleration. Informal testing with a GPS-based performance computer revealed 0-60 times for the AWD version in the 6.5-6.6 second range. Though we were unable to test it, the FWD version felt even quicker. The transmission and throttle mapping give the 2013 RDX a very snappy feel pretty much all of the time. This is a huge departure from the previous RDX, which seemed to be napping most of the time. Notably, Acura has programmed the transmission to drop a gear on slight grades in order to prolong the time the engine can operate in VCM mode. This has several effects - 1) Acura has determined that this is more efficient than lugging the engine in a taller gear and operating in full 6-cylinder mode, 2) the engine never feels like it's lugging to go up a hill, and 3) if you do need to tip in the throttle for a bit more thrust, the VCM system will quickly engage the idled cylinders and you have full availability of torque, instantly. The best part is that it all feels very natural and intuitive while driving the vehicle, and the RDX never feels flat footed.
Also gone is the RDX's SH-AWD. So what? The only way the original RDX could have seriously benefited from the added expense and weight of the SH-AWD system would have been if it were offered with a 6-speed manual transmission. (Side note: if that were ever the case, then maybe Acura would have managed to sell a few of them to the 30 year old "Jason" target that they had originally targeted). The new AWD system (shared with the CR-V) is simpler, lighter, and less costly. Most of the time, it's not even engaged, for the sake of fuel economy. During normal launches, 90% of the torque goes to the front wheels. In extreme situations, such as slippery hill climbs, up to 50% of the engine's torque can be diverted to the rear axle. Whatever, 99% of RDX drivers will never be able to tell the difference.