Supercharging The Northstar
By Frank Markus
Behold Cadillac's first production supercharged engine. Its official SAE-certified horsepower rating of 469 is the highest for any factory Cadillac, including all the jumbo-block SAE-gross-rated behemoths of the 1960s and early 1970s. Making power is all about getting air into cylinders. This can be done the Corvette Z06 way, using great big lungs, or by forcing air in with a blower. Cadillac reckoned the latter approach had a better chance of delivering the refinement and smooth idle demanded of a $77,090 car.
Air enters through an 80mm throttle body, flows around back of the engine and into the valley, where it's sucked up into the largest production Roots blower going. Spinning at 2.1 times crank speed, the air is pressurized to 12 psi before flowing up through a Laminova intercooler (water runs through tubes lined with closely spaced fins). The cooling fins drop pressure to 10 psi and quell the blower pulses. Air then U-turns and flows straight down into the intake valves to meet its octane-fueled destiny. Intake and exhaust valve timing are variable. Spent exhaust gases exit via extrude-honed ports, through cast manifolds and out through oversize catalysts and twin 2.5-inch sewer pipes.
The 469 horses arrive at 6400 rpm, but at least 395 of the 439 peak pound-feet of torque are available between 2200 and 6000 rpm. Fuel economy trails the naturally aspirated STS by three mpg city, six highway. And the idle quality is better, thanks to the added rotational inertia. There's way more to this Northstar than just a bolt-on blower, though.
1. The aluminum block is sand cast instead of die cast, necessitating 2mm smaller bore for better fatigue life.
2. Block and head castings undergo special T7 heat treatment and stabilization for strength.
3. Intake valve seats are copper infiltrated for better heat dissipation and wear.
4. Head gaskets reinforced to withstand 9:1 compression plus 10 psi boost.
5. Bigger oil jets cool the pistons with three gallons of oil per minute.
6. Oil pump, filter are higher capacity.
7. Two mufflers quiet intake roar upstream of supercharger.
8. Starter lives below blower in the valley for improved life (no road splash).
9. Low-restriction domino-shaped mass-airflow sensor replaces screen type
Read more: http://www.motortrend.com/roadtests/...#ixzz1wdHF2udF