Cadillac Power

Sometimes is seems like it is easier to make power in our world. Fat cams with nasty fast ramp rates, fabricated tube headers, straight-cut gear drives, un-silenced intakes, straight through mufflers, and all the other harsh equipment doesn't matter at all--it just needs to make power. The OEM's work in another world. In their world, smoothness, broad torque, durability, emissions and mileage are just a few of the hurdles that need to be crossed before the subject of outright power production can be addressed. Making big power in that world is a whole different game than in the unconstrained performance and race aftermarket.

If you happen to be Cadillac, the bar goes up that much further. No, for these guys the level of nastiness that would be acceptable in say a Camaro, or a Mustang isn't near the mark. These guys are under the gun to deliver engine qualities on par with the worlds best automakers in terms of refinement, sound and NVH. In developing the Supercharged Northstar V-8 for the new Cadillac STS-V, GM set it's sight high. Greg Prior, development engineer and Northstar V-8 SC project manager relates, "We wanted total performance, meaning excellent idle quality, smooth throttle response and great top end power." "The innovative new supercharger module and Northstar's infinitely variable valve timing proved to be ideal mutually supporting systems to combine high performance and exceptional refinement." To achieve a high level of refinement while delivering the output levels demanded today requires advance engineering, and the application of today's finest technologies. There's something to be learned in the application of these technologies that anyone truly interested in high performance can gain from.

Cadillac's new supercharged Northstar 4.4 liter (267 cid) V-8 (designated RPO LC3) is a showcase of advanced engine technology. The fact that it achieves a surreal specific output of 1.65 hp per cube while under Cadillac's stringent requirements for refinement is a testimony of the advancement in OE engine development. Output is pegged at 440 SAE net hp at 6,400 rpm. Yes, folks, you read that right, a stock Caddy with peak output at a rpm level you'd expect to find from a lumpy and radical street rat's smallblock. Unlike most high-rpm performance engine's, this Caddy isn't dependant on a set of 4.56s out back and a deep drag-race converter to get on the hump of the torque curve. The supercharged Northstar dishes out within 90 percent of it rated peak torque of 430 lbs.-ft. at 3,600 rpm at any point in the power curve from 2,200-6,000 rpm. That's the notion of a broad and flat torque curve taken to an extreme. Engine pros may take note of the 2,800 rpm spread between peak torque and peak hp. More than notable, that kind of broad shouldered manliness in a power curve is unachievable without a healthy dose of the latest engine technology.

The LC3 engine retains the architecture of the successful Northstar engine family, but this particular engine is anything but a standard unit fitted with a huffer. The most obvious clue is a change in spec for the bore size, which is modestly reduced from 93mm to 91mm. In fact, over half of the component parts of the supercharged LC3 are new or heavily revised, including every major structural component of the engine. Naturally, the compression ratio has been altered, dropped from the normally aspirated engine's 10.5:1 ratio to 9.0:1, to make way for the forced atmosphere. That pressurized induction is courtesy of a roots-type supercharger unique to this engine. GM considered the options available in forced induction, including turbocharging, as well as screw and roots-type positive displacement superchargers. The positive displacement supercharger was given the nod for the ability to provide instantaneous response. A roots blower was selected in favor of a screw type for the former's greater efficiency, particularly at part throttle, as well as its seamlessly smooth operation. While roots superchargers are nothing new, the LC3's blower is.

SUPERIOR SUPERCHARGER
The heart of the supercharger is a new "high twist" rotor design developed by GM Powertrain, in conjunction with Eaton Corporation. This design is more efficient and provides more airflow than any other OEM helical roots-type supercharger. While the revised helical rotors are new, the real twist is in the packaging and layout of the supercharger. Termed a "Power Module," the system incorporates the supercharger, intake manifold, and intercooler into an integrated assembly. This arrangement greatly simplified the design, eliminating many of the components and ducting found on other supercharger systems. In effect, its not so much a supercharger added to the engine as a supercharger designed-in as part of the engine. A more deliberate routing of the compressed gasses and resulting airflow efficiencies are gained.

The airflow enters the supercharger through the throttle body at the rear of the assembly, and is compressed by the rotors, exiting under boost pressure at the forward position between the two rotors. From there the air passes upward through the intercooler cores, and is shuttled outward by the plenum to the runners which feed from the top of the assembly. Routing of the runners is a direct downward shot into the cylinder heads' intake ports. The flowpath is much more compact and direct than is typical of other OEM supercharger applications, and the straight manifold runners are a key element in this engine's power production capabilities.

In any supercharger application such as this, the question of adiabatic efficiency must be carefully considered. Simply put, compressing the induction gasses is a heat generating exercise, so pressurizing the induction in an effort to raise output also results in considerable heat gain, which is contrary to that end. This nuisance was addressed by the development of an all-new integrated liquid to air intercooler. The Tubular Laminovo intercooler cores were developed specifically for this application, utilizing high fin density for thermal transfer efficiency in the four-core intercooler integrated in the top of the power module, just below the plenum.

VALVETRAIN VARIATIONS
One of the key elements in achieving the broad output of the LC3 is the variable valve timing (VVT) system. With VVT, the seemingly opposed objectives of smooth and torquey low-end output, and massive specific output to a peak at 6400 rpm become possible, using individual hydraulically actuated phasers on each of the four camshaft. "Four-cam VVT is an exceptional performance enabler, but also provides the control flexibility needed for highly advanced NVH and emissions characteristics," said Dave Caldwell, Northstar V-8 SC development and calibration engineer. "The supercharger module and VVT system complement one another, resulting in a genuine luxury and performance engine."

This system allows the camshaft phasing to be altered in relation to the piston position, as well as in terms of event timing between the intake and exhaust camshafts. The VVT system was introduced last year on the normally aspirated Northstar 4.6 liter V-8, and the system received all-new command strategy optimized for the supercharged 4.4 liter application. The variable valve timing system makes it possible to target optimal idle quality, control cylinder pressure and detonation, and enhance drivability, while providing for the high-speed breathing necessary to turn a number at the top of the powerband. Another advantage of the system is a reduction in exhaust emissions, which effectively eliminated the need for supplemental emissions equipment in the form of air injection or exhaust-gas recirculation systems while meeting today's stringent emissions standards.

BETTER BELOW
Though the supercharger and induction are at the center of most of the attention surrounding this new engine, the balance of the engine package was substantially improved as well. The block used in building the supercharged Northstar engine is an all-new casting, featuring revisions not only to accommodate the changed bore size, but also to improve durability under the loads imposed by high-output. Highlights here are a new oil galley, added to feed oil to the piston-cooling jets; a semi-closed deck structure for improved water-jacket flow; upgraded materials and revised ribbing for strength. The block carries the premium forged rolled filet steel crank newly introduced in the '04 normally aspirated engine. The rods are an upgraded design, manufactured in a heat-treated powdered metal process, and are bushed for larger 24mm piston pins. The pistons are redesigned for strength and to match the new compression ratio requirement, and are hard anodized to cope with the high specific output and heat in the supercharged applications. Piston cooling via a direct oil jet further improves durability and detonation tolerance. The oil pump has been upgraded to meet the increased oil flow demand, with more displacement for a higher rate of flow.

The cylinder heads are laid-out in the familiar pent-roof four-valve arrangement. For this application the combustion chamber has been revised. To aid in the exhaust flow requirements in a boosted application, the exhaust ports are abrasive machined for a smooth, flow-enhancing, surface and shape using the extrudehone process. To aid in heat transfer, the valve seat material is copper infiltrated, providing improve conduction of the higher heat developed under boost conditions. Providing the cylinder heads' seal to the new block's thicker deck are multi-layer steel head gaskets (MLS), a construction that has become popular in performance engine building in recent years.

Like the new hand-crafted LS7 Corvette engine, the LC3 will be specially assembled at GM's new Performance Build Center in Wixom Michigan. Each engine is hand assembled by a specialist engine building technician. The facility is dedicated to crafting engines for specialty applications such as the Cadillac STS-V, in an environment akin to custom race engine assembly. Each engine is viewed as an individual unit, and each is seen through the assembly process as the responsibility of a dedicated builder.

The engines are rigorously inspected throughout the process, and hot tested in a 20-minute run cycle upon completion. Timothy Schag, the site manager of the Performance Build Center explains, "This process brings a higher level of quality, because each builder is personally involved in every aspect of the assembly." "It was important to step away from the high-volume world we all had lived in for so long and soak in the cadence of these specialized environments." "We learned a lot and established a low-volume manufacturing system on par with the worlds best niche builders, but we didn't lose sight of the quality already in place at GM."

Much of the technology wrapped in the development of this supercharged wonder may eventually be incorporated in the performance engines we build. Sure, the advantages of positive displacement superchargers have long been exploited by serious performance fans but the technology here goes far beyond that. The sophisticated engine management, four-valve overhead cam cylinder heads, variable valve timing and other advance features of the latest from GM illustrate the state of the art in OE engine development. While you may not yet be able to apply it all to your dragstrip machine, if your pockets have the depth required to handle it, it is all available now in the latest Caddy.

LC3 ENGINE SPECIFICATIONS
Type: 4.4L DOHC 32 valve 90()() V-8
RPO: LC3
Manufactured: Performance Build Center, Wixom, Mich.
Displacement: 4371 cc (267 ci) Bore x Stroke: 91 mm x 84 mm
Compression Ratio: 9.0:1
Valve Configuration: Dual overhead cam (4 valves per cylinder)
Valve Lifters: Roller follower with hydraulic lash adjusters
Valve Head Diameter: Intake: 36 mm
Exhaust: 29 mm
Firing Order: 1-2-7-3-4-5-6-8
Engine As Shipped Weight: 229.7 kg (506.4 lbs.)
Engine Control Module: Delphi E67 ECM, 40 MHz control unit, 2 megabytes external flash memory and 128 kilobytes external SRAM
Additional Features: Piston spray cooling Friction washers at front of crankshaft Platinum tip spark plugs
Fuel System: Sequential Fuel Injection Returnless system
Injector flow rate: 40 g/s Premium required, 91 minimum octane
Horsepower: 440 (328 kW)@ 6400 rpm (estimate)
Torque (lb-ft): 430 (583 Nm) @ 3600 rpm (estimate) 90 percent of peak torque available between 2200 and 6000 rpm
Fuel Shutoff: 6700 rpm
Emissions Control: BIN8/EURO 4 compliant Close-coupled catalytic converters EGR and AIR not required
Oil: Synthetic 5W-30 9 qts. with filter
Block: Upper - sand-cast 319 T7 aluminum, Lower - die-cast aluminum
Bore spacing: 102 mm
Cylinder Head: 319 T7 semi permanent mold cast aluminum alloy with polished exhaust ports
Supercharger / Intake: GM patented integral design. GM specific helical Roots rotor set, cast aluminum case 2.0L (122 ci) displacement 2.1:1 pulley ratio, Four laminova style intercoolers Modulated bypass
Crankshaft: Forged steel with rolled fillets
Camshafts: Cast nodular iron
Cam Phasers:
Intake: Initial timing 133 degrees ATDC with 40 degrees advance authority
Exhaust: Initial timing 117 degrees BTDC with 50 degrees retard authority
Valve Lift: Intake: 10.5mm (.413 inch)
Exhaust: 10.0mm (.394 inch)
Duration @ .050"
Intake: 202 degrees
Exhaust: 214 degrees
Pistons: Cast aluminum, polymer coated, anodized top land 5.4mm, full floating 24mm pin
Connecting Rods: Powder Metal with heat treatment
Length: 151 mm
Exhaust Manifold: Cast nodular iron Accessory Drive Three belts
Rear: Alternator
Middle: AC, PS and water pump
Front: SC

TOTAL AIRFLOW
The supercharger is undeniably the key feature of the LC3, and as with any forced induction engine the objective of the system is to drive airflow through the system, inducting a greater charge with each cycle. The roots-type blower installed on this Supercharged Northstar engine takes a flowpath very different than that which is the norm in traditional GMC blowers familiar to hot rodders. The flow path as illustrated here is from the rear of the case, moving the air forward, upward, and to the centerline of the rotor housing. In the development process, the attention to airflow was not limited to just the supercharger. Here are some of the highlights.

The use of low restriction mass airflow sensors and air cleaners to reduce restriction and enhance flow.Induction tubes, which split and run along the upper sides of the engine before rejoining at the rear-mounted throttle body, that were developed with CFD (computational fluid dynamics) to deliver the required high airflow with low restriction.

Induction silencers, integral to the new induction tubes, co-developed by GM Powertrain and WocoTM to markedly reduce induction noise without reducing airflow.

High-flow Northstar V-8 cylinder head ports that are further refined with ExtrudehoneTM abrasive surface treatment. This patented process polishes the ports to improve flow.

Specific exhaust system, tuned for low backpressure, improves power for the STS-V. Larger diameter outlets on the close-mounted catalytic converters are used in the STS-V exhaust system.