How do you put an engine designed for front-wheel-drive luxury sedans into a rear-wheel-drive sports car?
Not easily, discovered General Motors' Powertrain division. But nobody was complaining last year when the automaker asked engineers to gin up a hotrod version of Cadillac's next Northstar V-8 for the new Cadillac Evoq concept roadster.
The Northstar is normally a transverse-mounted engine, and it had to be reworked extensively by a small team of engineers for its first-ever duty in a rwd car. To fit the engine into the Evoq, the engineers virtually had to redesign the vaunted Northstar, altering its architecture, the way it cools and lubricates itself and even the way it breathes.
But the project showed GM how much creativity can flow from dedicated people working under a tight deadline. The group pulled it off in less than one year, an accomplishment that makes John Zinser beam.
RALLYING THE TROOPS
The soft-spoken and serious Zinser is the chief engineer for GM Powertrain's Premium V department, which directs Northstar-related activity. Zinser was handed the assignment in February 1998, just three weeks after moving over from Powertrain's transmission department. There, he had been engineering manager on the Northstar's 4T80-E automatic transmission.
'The Evoq's designers were trying to show the styling direction Cadillac is taking,' Zinser said. 'They came to powertrain and said we also want to showcase potential engine technologies.'
Speed was essential. The Evoq had a date with the world press the following January at the 1999 North American International Auto Show in Detroit.
Zinser's 14-member core team volunteered to sacrifice evenings and weekends while maintaining a regular workload on other GM projects. In total, about 150 people put their fingerprints on the Evoq's nonproduction engine, he said.
'From the point we said that we want to do this piece and got everyone together, we had an engine running on a dyno in about six months.'
The finished powerplant generates 405 hp at 6,400 rpm and 385 pounds-feet of torque at 4,000 rpm, GM says. The Northstar in the 1999 Cadillac Seville STS, by comparison, generates 300 hp at 6,000 rpm and 295 pounds-feet of torque at 4,400 rpm.
RISING TO THE CHALLENGES
The starting point for the Evoq's motor was the next-generation Northstar, which will debut on 2000 Cadillac DeVilles. The all-aluminum, double overhead cam, 32-valve V-8 features several changes from the current Northstar. Engineers revised the combustion chamber and added a more efficient valvetrain. The valvetrain uses roller finger-follower valve lifters, or valve rocker arms that have small low-friction wheels, not pads, that ride the turning cam lobes.
The project was fraught with serious challenges. They include:
Cooling: Turning the engine 90 degrees inside the Evoq created problems. Cooling was a big one. In the regular Northstar, the water pump is on the back of the engine to take advantage of the dead space over the fwd transaxle. For the Evoq, Zinser said, 'we had a choice of carving a hole in the HVAC module or moving the water pump.' That meant designing a new water pump and changing the route that water follows through the engine - a huge engineering task.
Timing: A prototype variable-valve timing system graces both sets of intake and exhaust camshafts. The system constantly varies the timing of the valve movement to maximize power delivery and minimize emissions. Electromagnetic valves at each shaft control the timing adjustments by directing oil under pressure to one side or tihe other of a piston located on each camshaft.
The piston rotates the camshaft by alternately pushing or pulling on a worm screw, allowing up to 40 degrees of camshaft rotation.
Castings: The team also came up with a new design for a supercharger. It packages the conventional Roots-type rotors, the water-to-air intercooler, and the intake manifold passages in a single casting. The patented design saves weight by requiring less bolting hardware and fewer joints to seal. Part of the design is a bypass valve controlling the delivery of boost to the engine. The valve eliminates boost at low speeds, when supercharging is not needed.
Components: New powdered metal forged connecting rods, special forged aluminum pistons and a steel crankshaft clamped in bearing supports reinforced with steel bands were created to strengthen the engine's bottom.
The exhaust valves are nickel coated, and the valve seats copper coated for better heat dissipation. Engineers changed the thread pitch on some studs for more strength.
Zinser would not say which of the Evoq's engine tweaks will make it on production vehicles. 'We tried to show what was possible with this package. The platforms can make the decisions about what is right for their vehicles.'
In the meantime, some at Powertrain are eager to take on another project like the Evoq. Said Zinser: 'We have numerous people already putting their hands up volunteering for whatever comes next.'