Luxury cars must provide quiet, ample, refined power at all times, and the driver needs to be able to meter that motive force smoothly yet decisively. The engine and transmission should not intrude upon the cabin, and they should work harmoniously to deliver acceleration when and where it is requested. Such sophistication, combined with newfound American interests in fuel economy, vaulted the least powerful Lexus into first place and left the highest horsepower Acura in the basement.

3rd Place – Acura RL
Acura needs no other argument that it needs a V8 than this: Despite unanimous praise for the RL’s engine from our test drivers for its smoothness and refinement, a distinct lack of torque made the car feel sluggish unless we used the paddle shifters on the steering wheel or toggled the gear selector to keep the revs up. And when we did that, fuel economy tumbled dramatically, as evidenced by our 16-mpg test average, significantly less than EPA ratings of 18 mpg in the city and 26 mpg on the highway. Making the most horsepower (300 at 6,200 rpm) and down just 10 lb.-ft. of torque from the Infiniti (260 lb.-ft. at 5,000), the Acura’s 3.5-liter V6 nevertheless felt winded when asked to perform from mid-range speeds.

Unfortunately, this lack of response when we seemed to want it most overshadowed the Acura RL’s slick Super Handling All-Wheel Drive (SH-AWD) and its subtle off-the-line launch character, which was a refreshing change from the Infiniti’s jolt of power and the Lexus’ delay in initial acceleration. But, since we tested the cars on sunny days in Southern California, it is entirely possible that in rainy or snowy climates the RL’s smoother power delivery and sophisticated SH-AWD may have produced a higher powertrain ranking for Acura. SH-AWD is unique in that it not only distributes up to 70 percent of engine output to the front or rear wheels as needed, but it can also send as much as 100 percent of available torque to drive the outside rear wheel when cornering. Acura says this feature of SH-AWD dramatically improves steering feel, handling, and stability. But more on that later. For now, given the conditions under which we tested the vehicles, our staff ranked the RL’s powertrain in third-place.

2nd Place – Infiniti M35x
Unimpressive fuel economy and an indecisive transmission kept the 2006 Infiniti M35x from placing better than second-place in our powertrain rankings. We managed to get just 15.5 mpg during our test, less than the EPA estimates of 17 in the city and 24 on the highway. That’s plenty of premium fuel for which to pay, and that’s what the M35x’s 3.5-liter V6 engine requires to generate 280 horsepower at 6,200 rpm and 270 lb.-ft. of torque at 4,800 rpm. Everyone on staff praised the engine’s performance, including its more vocal nature. Unlike in the Acura and Lexus, you’re always aware of this V6’s purr.

Power flows to all four wheels through a five-speed automatic transmission that Infiniti says is equipped with adaptive software designed to learn your driving style and time transmission shifts accordingly. Trouble was, each of our three editors noted its tendency to delay downshifts in automatic mode. Switch to manual shifting, and enjoy short throws of the gear selector and rapid-fire response from the transmission. Plus, Infiniti has added an entertaining rev matching feature on downshifts. Infiniti’s ATTESA-ETS (Advanced Total Traction Engineering System for All Electronic Torque Split) splits torque front and rear, and the company says that in tandem with the standard Vehicle Dynamic Control (VDC) system – stability control to us common folk – each wheel receives the appropriate amount of torque when needed. On the dry roads around Orange County and Malibu, it worked fine. What we wished for was a transmission with better timed shifts.

1st Place – Lexus GS 300 AWD
Seriously, it wasn’t just the as-tested average of 20.5 mpg that the 2006 Lexus GS 300 AWD delivered that landed it at the top of the powertrain heap. And it certainly wasn’t class-leading power and torque figures, since the 3.0-liter V6 musters just 245 horsepower at 6,200 rpm and 230 lb.-ft. of torque at 3,600 rpm. Rather, it was commentary from our staff about smooth, silky, silent, and refined power delivery, coupled with a responsive six-speed sequential shift automatic.

Aside from a slight delay in off-the-line response and occasionally hard downshifts under full-power requests made at cruising speeds, nobody could complain much about the Lexus’ wonderful motor and impressive transmission. Peak torque arrives quickly, and the Lexus weighs just 3,760 pounds, so it feels faster than you might expect after a cursory examination of the numbers. And with EPA estimates of 21 mpg city and 27 mpg highway, the GS 300 AWD’s premium fuel requirement produces less frequent holes in your wallet. Plus, the adaptive transmission learns quicker than the Infiniti, and includes three modes of operation: Power, Normal, and Snow. Stability and traction control systems mete out the power to all four wheels, though, as with the Infiniti, the Lexus cannot match Acura in terms of its AWD system’s technical sophistication.

True, the Lexus has neither the most sophisticated nor the most entertaining powertrain in this trio, but for buyers of luxury sedans, it is the most refined, and that’s why we ranked it as best.