One of the reasons that we at Autoblog so enjoy the car show season is the cutaway engines that some manufacturers put on display. Let's face it - with the heart of our cars nowadays more likely than not obscured behind a variety of plastic covers, this is a rare opportunity to catch a glimpse of more than the oil fill cap. We'll start by poking the camera lens into Cadillac's supercharged 4.4L supercharged Northstar, an engine that provides 469 HP at 6400 RPM and a peak of 439 lb-ft of torque at 3900 RPM (that's 106.6 HP/L and 99.8 lb-ft/L for those interested in such stats).
Hop the jump to see hear more about the blown Northstar and let us know if you like such features so we can get to work on generating a few more.
The most interesting attribute of this engine is the intake tract. Below, at the upper left side, the beginning of the large intake duct can be observed. From there, the air splits and travels around each side of the engine.
Hey, there's the oil cap! And what's that weird perforated thing behind it? I'm not sure, but it looks like a muffler of some sort (the housing has been cut away to show the guts, of course). Supercharged engines typically don't generate appealing intake noises, and given the target audience for this engine, the typical whining and whoosing sounds would not be acceptable.
From here, the tracts recombine and dump into a throttle body, mounted at the rear of the supercharger. This, of course, is a throttle-by-wire engine.
Here's where things get a bit wild. The supercharger compresses the intake charge and discharges it upwards, where the intercooler does its best to remove the heat generated when compressing air.
Below, one can see the long path the air has to take from the intercooler down to the intake port, through the intake valve, and into the combustion chamber. On a naturally-aspirated engine, such a tract would not be acceptable on a high-revving engine, but once forced induction is applied, the rules change somewhat. The benefits of intercooling (increased charge density and decreased propensity for detonation) are well worth a more restrictive intake path - just turn up the boost another few PSI!
When viewing the bottom end, the Northstart starts to show its age (remember that it's over a decade old), as the block ends right at the crankshaft centerline. A beefy girdle runs around the main caps, though, and provides an improvement in rigidity and strength. The gear-looking thing in the middle of the crankshaft is the tone ring for the crankshaft position sensor (look closely at the valley in the 6th picture, and one can see the sensor that picks up the teeth of tone ring).
Below is a nice shot of the chain drive for the valvetrain, including the actuators for the variable-valve timing. Oil fills the cavities in the actuators, and the cam and crankshaft sensors are used to provide closed-loop control over cam timing. Obviously, with an actuator for each cam, it's possible to independently change the timing of the intake and exhaust events. This makes it possible to widen the powerband while decreasing emissions - something everyone can appreciate.
Well, there you go - a five-minute walk-through of an engine that is the result of two decades or so of development.