2006 Cadillac STS-V

Alex P

Ann Arbor- Push the starter button to the right of the Cadillac STS-V's steering wheel, and the supercharged V-8 leaps to life while the driver-information LED display briefly illuminates the greeting, "Ready for STS-V?" After spending a week with the most powerful Cadillac ever produced, we'd like to throw that question back at Cadillac, and at GM: Are you ready for STS-V? Is Cadillac, which has been scratching and clawing its way back to respectability, really prepared to go head-to-head with AMG-tuned Mercedes-Benzes and M-badged BMWs? Or is the STS-V, like the CTS-V, a noble, competent, and entertaining effort that ultimately is compromised by unattended details?

If it is, it's certainly not for a lack of V-series enthusiasm among GM engineers, who giddily describe the modifications they've made to the base STS to arrive at the STS-V. The most important of these changes, of course, is the new, supercharged, 4.4-liter version of the Northstar V-8, which produces 469 hp and 439 lb-ft of torque, increases of 149 hp and 124 lb-ft over the normally aspirated 4.6-liter V-8.

Development of Cadillac's first supercharged production engine extended beyond simply nestling the Roots-type blower between the V-8's 90-degree cylinder banks. To fortify the Northstar for this assignment, the cylinder bores were reduced from 93 to 91 millimeters, which resulted in the smaller displacement, and the engine block is sand-cast rather than die-cast, for a 40 percent improvement in fatigue strength. New cylinder heads, heavy-duty pistons, revised connecting rods, and a lower compression ratio-9.1:1 versus 10.5:1-also help accommodate the additional output. The supercharger itself is a particularly well-packaged and well-engineered piece, with long, high-twist rotors generating the added air flow plus trick water-to-air tubular intercoolers with fins that look like the underside of a portabella mushroom. "The Northstar's four-cam variable valve timing allows us to exploit the blower's output," says engineer Greg Prior. "We're really exercising the cams."

Exercise your right foot, and the blower responds with a progressive buildup of power and rotor whine that's less intrusive than that of the supercharged Jaguar V-8. The Northstar, though, does not produce the locomotive-like thrust of the Mercedes E55 AMG's mighty 5.4-liter supercharged V-8. "We match the E55 in power," Prior boasts, "with one liter less displacement." True, but the Northstar is down 77 lb-ft of torque on the AMG V-8, and it's the E55's seemingly endless supply of torque, the accelerative forces that bury you into your seat as if you're in a Gulfstream V on takeoff, that make the Mercedes worth its premium over the Caddy.

Not that the STS-V is anything like slow. In our tests, it clocked the 0-to-60-mph run in 5.3 seconds and the quarter-mile in 13.9 seconds at 105 mph, as compared with 7.0 seconds and 15.3 seconds at 95 mph, respectively, for the stock STS V-8. (The last time we tested the E55, in December 2002, we saw a 5.0-second 0-to-60-mph time and ran the quarter-mile in 13.1 seconds at 112 mph.) You will not want for power in the STS-V, but the all-new six-speed manu-matic transmission doesn't always transfer the engine's goods to the rear axle as smoothly as you would expect, whether it's in fully automatic mode, on the sport setting, or in manual-shift mode, when it has an especially difficult time with the two-three upshift.

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