1994 Cadillac Eldorado

The Northstar Engine

For the non-tech people who are reading this, it may be interesting to give some basic information on engine design, without making the reader feel like they need to attend any distance learning MBA programs. So what makes the Northstar engine so very special ? First of all it is of the Dual Overhead Cam (DOHC) design. That means that camshafts are not located centrally, as in a classic engine. Instead the camshafts are mounted above the valves. This means that there is no longer need for pushrods or rocker arms, eliminating a lot of internal friction and power loss. "Hey", I hear you say. "You are constantly talking about camshafts (plural ), why's that ?". You are right, "normal" engines only have one camshaft, which is centrally located in the V-block. The Northstar (and some other American and European V8's) has multiple camshafts. Each cylinder head has two camshafts, mounted above the valves. The reason for having more than one camshaft per cylinder head, is the amount of valves that are involved in the Northstar. Again, "normal" engines only have two valves per cylinder (one intake and one exhaust). In order to allow better engine breathing and better cylinder filling, the Northstar has two intake valves and two exhaust valves per cylinder, totaling 32 valves. Having only one camshaft per head, would result in this camshaft operating on 16 valves. Not only would this require a special valve layout, but it would also result in an enormous loss due to unnecessary friction. With a DOHC design, one camshaft operates the intake valves, the other one the exhaust valves. So as a matter of fact, the Northstar has four camshafts, compared to one as in a classic V8 (like the Cadillac 4.9 liter). Another reason why the Northstar is so special, is that is made completely out of aluminum. This makes the engine considerably lighter than one in cast iron. The Northstar engine weighs about 230 kg, about the same as the 4.9, despite the additional valves, camshafts and related chain-drive components. When you make a car lighter, you have less dead mass to drag with you, and you get an overall more performant machine (the so-called horsepower to weight ratio). The Northstar engine has a host of other improvements over the 4.9, amongst them a special modulating intake manifold and a special kind of distributor. A normal engine uses a device which contains a rotor or cam to close contact points and create a spark. This always implies using moving parts, subject to wear. The Northstar Engine does not have any moving parts in its iginition system. Magnetic sensors are positioned at the crankshaft and camshafts. Those sensors are triggered by notches in the crankshaft and camshaft. These generate an ON-OFF pulse wave, similar to the open-closed position of classic breaker-points. This wave is interpreted by the ignition module, containing 4 ignition coils (1 coil per 2 opposed cylinders). As the wave signal enters the ignition module, a high energy voltage is generated in the appropriate coil, resulting in two simultaneous sparks in the opposing cylinders. Since one cylinder is at its exhaust stroke, this spark will have no effect. This system is called waste spark ignition