In our last installment of the Cadillac Northstar story, we reviewed the engineering decisions made early in the engine’s development. From the sensible choice of 4.5 liters of displacement (4.6 in production) to the hubris of consumer focus groups filled with aging current owners, the project rolled forward but faced many engineering challenges. The development was daunting as Cadillac’s first dual overhead cam V8 engine after decades of overhead valve power plants. The difficulty of pairing a cast aluminum block to iron cylinder liners was complete, but engineers opened up a new can of worms with the induction system.
In brief, a car’s induction system is responsible for sending fuel and air into the combustion chamber. Major components of an engine’s induction system include the intake manifold, injectors, throttle body, valves, and the air filter assembly. In the forefront of engineers’ minds was the “high technology” phrase that kept being repeated. Top management said it, the customer said it, and Cadillac’s flop of a 4.1 said it right on the engine block. High technology!
To that end, there were many prototype designs for the induction system which dragged on for some time. It would prove to be the most difficult part of the engine’s development, and indeed problematic when it hit production as well. Cadillac’s engineers decided to go with an intake manifold made of magnesium.
General Motors had little experience with magnesium in any of its engines, but decided Northstar was the time to step it up. Many automotive applications are not suitable for magnesium components: Magnesium alloys have a low strength at high temperatures, and have poor resistance to corrosion. Magnesium is subject to all main types of corrosion, which includes galvanic, uniform, pitting, and stress corrosion.
Engineers proceeded anyway, as they heard the siren call of magnesium’s lightweight properties. Visions of the heavy small block V8s of the past filled their heads, and they wanted no part of that for the all-Northstar future. The manifold had to be tested extensively to ensure it was strong enough to last through extended high-stress engine usage without developing cracks.
Strength wasn’t the only concern, as during development there were issues with its design that caused backfiring. If the valves were stopped in a certain position upon engine shut down, unburned fuel was left in the intake manifold. Starting the engine again, the leftovers caused a backfire.
Engineers were not prepared to cut their losses with “the magnesium bucket,” as they called it, and had to rework the ignition to prevent the backfiring. This required a separate ignition coil system (more on that later). But at last the bucket was ready for production.
The induction system used a magnesium plenum housing, with glass-filled thermoplastic induction tubes. A magnesium design did cut down on machining requirements, as it was a more precise casting. The fuel rail assembly was made of nylon. PVC and EGR systems were both implemented in the design as well, for lower emissions.
All first-year Northstar engines featured a magnesium intake manifold. Immediately after development GM knew it wasn’t the best long-term course of action, and started another induction system program on Northstar. Engineers worked quickly to develop a composite (plastic) intake manifold instead. After the first year of engines, the manifold was switched to the composite version and customers were none the wiser.
A more successful engineering development for Northstar was its unique cooling system. The engine’s coolant pump was placed at the rear of the engine, and driven by the left side intake camshaft. This design allowed external coolant plumbing to be simpler. Included in the system was its party piece: four-cylinder operation after a complete loss of coolant.
The engine control module (ECM) included alternative programming upon a loss of coolant. After loss was detected, the ECM ran its overheating protection operation and changed the Northstar to run on four cylinders instead of eight. When those four cylinders got too hot, it would activate the other four. This allowed travel to a service location upon coolant loss, and prevented a driver being stranded.
To prevent backfiring, the aforementioned ignition coil system used four coils and one control module. Working in tandem with a camshaft position sensor, two crankshaft position sensors, and a wheel on the crankshaft, all were designed to make engine synchronization as fast as possible on startup. It was managed through a powertrain control module (PCM), which controlled spark and injection, reading and diagnostics. If any of the above failed, the engine was programmed not to start.
The PCM was also the overseer of the engine and transmission, ensuring all information on the powertrain converged in a single place. This advanced processor had an impressive 128 kilobytes of memory, or the same as a 1983 Apple IIe. With this power the PCM was able to manage monitoring, fuel economy, engine performance, and control the transmission based on acceleration inputs and whether the traction control system was intervening.
All the engines whiz-bang new features were well and good, but they needed a bit of marketing and packaging as they extended beyond the Northstar engine itself. Cadillac trademarked a name for this suite of performance and technology features, set to debut on the 1993 Cadillac Allanté (the brand’s halo car). A Northstar System was created.
Do we even use it? Cadillac was ready for the Nineties with a discontinuation of its old staid product, and the arrival of a new lineup of Northstar System-equipped front-drive performance luxury coupes and sedans. The time for Brougham had run its course. We’ll pick up there next week.
[Images: GM]
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