2002 Acura 3.2 CL -- Powertrain

— Torrance, Calif.

OVERVIEW
Both CL models come with an aluminum block, V-6 powerplant. The CL features a powerful, 225-hp VTEC V-6 engine, similar to the CL's sibling, the 3.2 TL luxury performance sedan.

The high performance CL Type-S model raises the CL's engine output to even higher levels. Several enhancements to the CL's VTEC V-6 engine, including a high-flow, dual-stage induction system and free-flowing exhaust help the CL Type-S develop a maximum 260 horsepower and 232 lb-ft of torque.

In addition, Acura's patented VTEC technology, first utilized in the NSX supercar, provides both the CL and CL Type-S models with an incredibly flat torque curve, boosting power and responsiveness at all engine speeds.

Both CL powerplants transfer their power through a 5-speed automatic transmission with Formula One-inspired Sequential SportShift system. As in the Acura NSX, the SportShift allows the driver to select the forward gears like a manual transmission while enjoying the convenience of an automatic transmission.

The CL's performance was not achieved at the expense of Acura's commitment to the environment, as both the CL and CL Type-S meet tough Low Emission Vehicle (LEV) standards. CL California models meet Ultra Low Emission Vehicle (ULEV) emission standards.

Powertrain Overview

Engine

  • All-aluminum, 3.2-liter, 24-valve, SOHC, VTEC, V-6 engine
  • 260 horsepower at 6100 rpm and 232 lb.-ft of torque between 3500 - 5500 rpm (CL Type-S)
  • 225 hp at 5600 rpm and 217 lb.-ft. of torque at 4700 rpm (CL)
  • Dual-stage induction system and high-flow exhaust system (CL Type-S)
  • Variable Valve Timing and Lift Electronic Control (VTEC)
  • Computer-controlled Programmed Fuel Injection (PGM-FI)
  • Direct ignition system
  • 105,000-mile tune-up intervals

5-Speed Sequential SportShift Automatic Transmission

  • 5-speed design improves acceleration and fuel economy
  • Quick-response Sequential SportShift allows semi-manual operation
  • Grade Logic Control to assist shifting when driving through hills
  • Direct-control automatic transmission is managed by the Powertrain Control Module (PCM) for smoother shifting
  • Large torque converter lockup improves performance and fuel efficiency

Emissions/Fuel Economy

  • CL EPA fuel economy of 19/29 mpg (city/hwy)
  • Type-S EPA fuel economy of 19/29 mpg (city/hwy)
  • All CL coupes meet LEV standards; CL California models meet ULEV standards
  • Electronically controlled Exhaust Gas Recirculation (EGR)

Noise Vibration and Harshness (NVH)

  • Smooth firing, 60-degree V-angle
  • Full-floating piston pins eliminate piston slap during warm-up
  • Elimination of separate camshaft holders allows for a more compact, rigid cylinder head
  • Lightweight pistons and connecting rods
  • Two hydraulic engine mounts
  • Transmission gear noise reduction through tighter gear-teeth-mesh contact ratio
  • High rigidity cylinder block (with additional strengthening ribs on Type-S)

ENGINE ARCHITECTURE
An advanced 3.2-liter, 24-valve, all-aluminum, 60-degree V-6 engine powers both the CL and the CL Type-S. Remarkably compact and lightweight, the CL powertrain incorporates a wide variety of advanced technologies, including the VTEC system, high flow air filter and throttle body along with a unique, dual-stage induction system exclusively on the Type-S.

ENGINE BLOCK
Die-cast and heat-treated, the compact aluminum block is extremely rigid, with a high natural frequency and minimal resonant vibration. The V-6's iron cylinder liners have their bore pitch set at 98-mm spacing to reduce overall engine size. The free-revving CL engine is oversquare with a bore of 89 mm and a stroke of 86 mm to give the engine a total displacement of 3210 cc.

The CL employs an engine cylinder bank V-angle of 60-degrees, allowing for a compact design with improvements in engine smoothness and reduction in overall bulk and weight. The block has an unusually short deck height, resulting in an overall reduction in the height and width of the assembled engine.

The Type-S engine incorporates separate, spin-cast cylinder wall liners that are cast into the engine block during the initial manufacturing stage. These spin-cast liners allow for a reduction in weight over traditional engine block cylinder walls and provide added heat dissipation to avoid engine knocking. Additionally, by reducing the number of machined surfaces, spin-cast cylinder liners simplify the manufacturing process.

CRANKSHAFT/CONNECTING RODS/PISTONS
A rigid, forged crankshaft and narrow 19 mm connecting rods allow a reduction in overall engine length as well as width. The connecting rods in the V-6 do not use conventional nut-and-bolt type fasteners, instead utilizing lighter bolts that thread directly into the rod and operate as "plastic-region" fasteners. These bolts allow a downsizing of the rod bolts while maintaining the proper clamping force and strength margins.

The V-6 incorporates compact pistons made from lightweight, cast aluminum alloy. The shape of the piston crown helps concentrate the fuel/air charge in the center of the combustion chamber to provide maximum volumetric efficiency, producing a 9.8:1 compression ratio in the CL. The Type-S achieves a 10.5:1 ratio thanks to a larger dome on the piston which provides a smaller combustion chamber volume. The pistons utilize a 3-ring design with the Type-S engine incorporating a unique angled top ring for an improved seal within the cylinder to accommodate the higher combustion pressure.

CYLINDER HEAD
The pressure-cast aluminum alloy cylinder heads reflect Acura's latest thinking in engine design. Utilizing 4 valves per cylinder and a compact combustion chamber with a generous squish area, the cylinder head is a key component of the high output CL engines. The Type-S engine also features special, race-designed intake valves to further improve flow into the combustion chamber.

The single camshaft in each cylinder head is installed from the timing-belt end of the engine, eliminating the need for bolt-on camshaft caps - a savings of weight and complexity. Driven by the crankshaft via a fiberglass reinforced toothed belt, the cams activate the valves by way of friction reducing roller followers.

VARIABLE VALVE TIMING AND LIFT ELECTRONIC CONTROL (VTEC™)
The Variable Valve Timing and Lift Electronic Control (VTEC™) valve train is a major contributing factor to the CL's remarkable combination of high power delivery and fuel efficiency. With the lift and opening duration of the larger intake valves altered automatically based on engine rpm, the engine develops strong low-speed torque without sacrificing high-rpm power.

The VTEC-equipped engine delivers substantial high-rpm horsepower, coupled with abundant torque in the low-to-mid rpm range. At low rpm, the VTEC intake valves follow a set of low-lift, short-duration cam lobes with timing that optimizes cylinder filling. Additionally, the timing of the intake valves is staggered and their lift is asymmetric, creating a swirl effect within the combustion chambers. This increases burn speed and improves combustion stability and allowable EGR rate. As the engine accelerates through 4400 rpm (4800 rpm on Type-S), the intake rocker arms transition to actuation by high-lift, long-duration cam lobes designed to optimize high rpm output.

The camshafts found in the Type-S engine further increase power output by providing longer intake valve duration, more valve overlap and additional lift for the exhaust valves.

DUAL-STAGE INDUCTION SYSTEM (CL TYPE-S)
Fitted on the Type-S model, is a high-performance, dual stage induction system which contributes substantially to the output of the 260 horsepower engine. This system uses a large, two-chamber intake plenum separated by a butterfly valve which is opened by an electric servo motor above 3800 rpm.

When the valve is closed during low-to-mid rpm operation, a resonance charge condition exists as pressure pulsations between cylinders assist the adjoining cylinder of each bank. In doing so, the volume of air filling the cylinders increases with the resonance energy generated by using the Helmholz principle. This Helmholz principle phenomenon results in improved cylinder charging.

When this valve opens at 3800 rpm, an inertial charge condition is generated and increased air filling continues when the manifold volume (plenum) is increased. This phenomenon utilizes the high flow mass to pressurize the manifold port air, producing a natural "supercharger" effect.

This increased airflow and cylinder filling is a primary contributor to the CL Type-S engine's additional power. Additional improvements were made to reduce air intake restriction and increase total air flow volume through a larger 64mm bore throttle body, a low restriction air induction intake and a high flow air filter.

PROGRAMED FUEL INJECTION (PGM-FI)
Controlled by a 16-bit, 32 MHz Central Processor Unit (CPU), the CL's Programmed Fuel Injection (PGM-FI) system monitors and controls numerous fuel system functions. Signals indicating throttle position, engine temperature, intake manifold pressure, atmospheric pressure, exhaust gas oxygen content and intake air temperatures are all processed by the CPU. It controls fuel delivery by injectors mounted in the cast aluminum, tuned-length intake manifold. The manifold features a large plenum chamber to help maximize airflow and increase power and torque. While tracking the operation of the engine with position sensors on the crankshaft and both camshafts, the PGM-FI CPU is also in constant communication with a similar CPU that controls the 5-speed Sequential SportShift automatic transmission.

EXHAUST SYSTEM
The CL's high-flow, dual-outlet exhaust system is designed to offer lightweight, low restriction performance while ensuring excellent emissions and noise control. To help the Type-S achieve additional horsepower, it allows greater exhaust flow through a larger diameter exhaust pipe, an increased flow catalytic converter and ultra-high flow capacity dual mufflers. These enhancements to the Type-S increase exhaust flow by over 30 percent compared to the CL. The Type-S exhaust has also been tuned to provide an aggressive, performance-oriented note while minimizing noise at cruising speed.

DIRECT IGNITION SYSTEM/KNOCK CONTROL
Proper ignition spark timing is critical to engine performance and emission control. This timing constantly changes from one instant to the next depending on a multitude of factors. If there is too little spark advance for the conditions, then efficiency suffers; if there is too much spark advance, then knocking (or pinging) can result in overheating and engine damage.

To ensure a properly timed spark, the CL relies on a new generation knock-control system. Based on a centrally positioned sensor in the block that "hears" the first traces of knocking, the ignition timing is advanced to the point of peak efficiency, but not beyond, even if fuel quality is less than the specified premium unleaded. This fine spark control allows the CL to operate safely and more efficiently with greater spark advance than its predecessor. Another refinement to the ignition system is the adoption of direct ignition coil units. These compact and reliable units are positioned directly in the spark plug access bores.

CONTROL OF NOISE, VIBRATION AND HARSHNESS
Though the CL's powertrain was engineered for uncompromised horsepower and torque, special effort was devoted to reducing noise, vibration and harshness (NVH). Key engine attributes were analyzed to develop engineering targets for smoothness and noise control. Both the CL and the CL Type-S engines reflect this effort with features like the compact, rigid aluminum block and its unusually high resonant frequency, a rigid forged crankshaft, die-cast accessory mounts and a stiff cast aluminum oil pan.

105,000-MILE TUNE-UP INTERVALS
The CL boasts engine tune-up intervals of 105,000 miles, between which only routine inspections and fluid changes are required. The roller-follower design of the VTEC valvetrain cuts friction and wear to the point that the screw-type tappet clearance adjusters do not require inspection until 105,000 miles, at which point the platinum-tipped spark plugs are also due for replacement.

DIRECT-ACTING CRUISE CONTROL
Even though the CL was designed as a true driving enthusiast's car, an electronic cruise control is provided for convenience on long trips. When engaged, the cruise control system's Electronic Control Unit (ECU) directly commands downshifts to the transmission ECU as required, allowing the vehicle to more closely maintain the set road speed even in hilly driving conditions. The convenient steering wheel-mounted cruise control buttons allow the driver to adjust speed in one mph increments or disengage the cruise control without touching the brake pedal by pressing the "cancel" button.

5-SPEED SEQUENTIAL SPORTSHIFT' AUTOMATIC TRANSMISSION
To maximize the performance capabilities of both the CL and CL Type-S, an advanced 5-speed Sequential SportShift automatic transmission was developed. This transmission was designed to enhance the sporty character of the CL while also providing smooth and effortless shifting.

The gear ratios were carefully chosen to match the engine's power characteristics. The wide ratio transmission's lower gears provide quick acceleration while the tall top gear ratio results in low cruising rpm's for reduced engine noise and lower fuel consumption.

The CL's transmission downshifts quickly with reduced shift shock, and is aggressively tuned to take advantage of the abundant power generated by the CL's engine.

By sharing the idler and third gear clutches, the transmission provides a total of five ratios without a significant increase in size or weight over typical 4-speed transmissions. Other improvements include the addition of a first gear one-way clutch for smoother shifts and a new heat exchanger design that moderates transmission operating temperature more quickly and with less complexity. An expanded torque converter lockup area provides a more direct driveline feel, similar to a manual transmission.

The CL's transmission uses a 16-bit, 20 MHz ECU operating in concert with the engine management system to apply Direct Control shift technology. Linear solenoids provide precise, real-time control of the clutch on/off pressure in the CL's transmission. With superior clutch-engagement accuracy, the sophisticated control logic operates smoothly under all conditions. To reduce noise, a bearing supports the idler shaft, and the gear-mesh contact ratio was optimized.

Multiple safety and control strategies use interaction between engine and transmission controllers to manage overall powertrain operation. By limiting engine output torque and/or transmission clutch pressure during shifts, sharp driveline shocks are eliminated. The engine is also prevented from exceeding 5000 rpm in neutral and park.

SEQUENTIAL SPORTSHIFT SYSTEM
Both the CL and the CL Type-S are equipped with a Sequential SportShift system, similar to the one originally introduced in the NSX sports car. The CL's SportShift transmission operates as a traditional automatic or puts gear selection in the hands of the driver, much like a manual transmission. By moving the console-mounted transmission selector handle to the left of the "D5" position into the SportShift gate, upshifts and downshifts can be commanded with a quick fore or aft motion. Gear selection is indicated by an LED display located in the tachometer face.

To foster the immediate feel of a manual transmission, in SportShift mode the transmission logic commands firmer shifts that are approximately 10 percent quicker than shifts in automatic mode. Additionally, the system is engineered to deliver a quicker response time to shift commands than other semi-manual automatic transmissions.

Typically, the CL's transmission responds to a shift command in just 0.35 seconds, with the total shift completed in just over 0.9 seconds from the time of the initial lever movement. These figures are quicker than those of semi-manual automatic transmissions of sports cars costing twice as much as the CL.

The Sequential SportShift system parallels the operation of a manual gearbox, but with built-in safety override features. The logic will not allow a downshift that would cause the engine to over-rev. When decelerating, the transmission will stay in the selected gear until the vehicle approaches a complete stop and then will shift into first automatically. During acceleration, except for shifting between first and second gear, the transmission will not up-shift automatically in SportShift mode. However, should the driver fail to upshift in time, the engine ECUs will cut off the fuel flow to prevent the engine from over revving.

GRADE LOGIC CONTROL
By monitoring throttle position, vehicle speed and acceleration/deceleration, then comparing these inputs with a map stored in the transmission computer, the Grade Logic Control System determines when the car is on a hill. The shift schedule is then adjusted automatically to hold the engine in a lower gear for better climbing power, increased downhill engine braking and reduced shift frequency.

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