Is 440 horsepower enough to keep up with the German hot-bloods?
BY CSABA CSERE / February 2005
Cadillac is determined to make inroads into the luxury market that's been dominated by the Germans for the past 30 years. The Detroit brand has steadily been introducing strong new products over the past three years. And like the premium automakers in Germany, Cadillac has established a performance division to attract wealthy hot-bloods as well as enhance the appeal of the entire division.
The first of these hot-bloods was the Corvette-engined CTS-V
that appeared last year. Now Cadillac has unveiled a hot-rodded version of the STS, the division's newest product. This STS-V
eschews the pushrod Corvette V-8 in favor of the well-established 32-valve, four-cam Northstar V-8, one that is, for the first time, energized by a Roots-type supercharger.
Spinning at 2.1 times crankshaft speed, the supercharger, which displaces two liters of air with each revolution, creates 12.0 psi of boost in the intake system. The inevitable temperature rise produced by this compression is ameliorated by four Laminova cooling tubes with closely spaced fins within the intake manifold. This intercooling system has its own dedicated heat exchanger in the STS-V
The Northstar engine gets the expected changes and upgrades demanded by this supercharging. This includes increased cooling flow within a reinforced block, oil-cooled pistons with a reduced 9.0:1 compression ratio, stronger rods, and a bore reduction from 93 millimeters to 91, reducing displacement from 4.6 to 4.4 liters for improved fuel economy.
To make the most of the supercharger's forced feeding, the Northstar SC, as it's called, also gets a low-restriction intake and exhaust system and Extrude Hone exhaust ports (imagine a really thick and highly abrasive toothpaste forced through the ports to smooth any rough edges).
All of this adds up to 440 horsepower at 6400 rpm and 430 pound-feet of torque at 3600 rpm. That's a useful 120-hp improvement over the standard STS V-8, but it doesn't exactly set new standards for the class. The R versions of the Jaguar S-type and XJ have 390 ponies. The Audi RS 6 had 450 horses. The Mercedes E55 has 476 horsepower. And the upcoming BMW M5 will have 500.
Still, this is enough power to keep the STS-V
competitive, especially as it is coupled to a brand-new six-speed automatic transmission, the GM 6L80. With a 6.00 ratio spread between first and sixth gears, this transmission should be able to fully exploit the blown engine's broad torque curve while delivering decent fuel economy. The transmission also provides for manual gear selection as well as Cadillac's excellent Performance Algorithm Shifting, which makes the transmission feel at home on tracks and winding roads.
To match the 38-percent power increase, the STS-V
gets numerous chassis changes. The front and rear cradles are reinforced. The engine is lowered to provide clearance for the larger transmission. The front and rear springs and the anti-roll bars are stiffer by 10 to 20 percent, along with much stiffer compression damping in the monotube Sachs shock absorbers. Even the steering gear was changed to a slightly quicker ratio to improve responsiveness.