In engineering terms, Honda doesn’t do anything by half measures. Take the new 2003 Accord, for instance. Technology is a given in the luxury and sport-sedan market, but the Accord is supposed to be a high-volume plain vanilla sort of car for people who want reliable, comfortable transportation and good value. For a “family car” (excepting the Accord Coupe, which has sporting aspirations and decent technical credentials) the ’03 Accord is loaded with enough tech to keep a rocket scientist happy. Available under the hood are two new engines, a 160 horsepower four cylinder displacing 2.4 litres and a 3.0 litre V-6 with 240 horses. Both power ratings are significant, and both come through a group of technologies that individually contribute little, but cumulatively sum to horsepower figures that were V-8 territory fifteen or twenty years ago. The SOHC four-valves-per-cylinder V-6, for example, has been redesigned with a new tuned intake system and manifold flowing through larger intake valves actuated by a three-rocker version of Honda’s VTEC variable valve timing system.
VTEC makes it possible to vary the relative timing and lift of the intake valves to optimize overall performance, netting good low-end torque as well as improved high-end horsepower.
Basic operation of the 3-rocker VTEC setup used on the 2003 Accord’s V6 is similar to that of the 2-rocker version used on the DOHC 4-cylinder, where rocker arms fitted with low-friction roller followers actuate the intake valves.
The heart of the VTEC system is a unique camshaft and rocker arm system. For each cylinder’s set of two intake valves, there are three rocker arms and three corresponding lobes on the camshaft. The two outboard lobes each have a profile maximizing cylinder swirl to suit low- to mid-rpm operation. The third or centre cam lobe has a dramatically different profile designed for longer duration and higher lift. This lobe profile is designed to optimize breathing and horsepower production at high engine speeds.
At low engine rpm, the outboard lobes operate the valves. During high-speed operation the VTEC computer sends a signal to a spool valve, which in turn delivers engine oil pressure to small pistons in the rocker arms. Oil pressure causes the pistons to move, locking all three rocker arms together. Once locked, the rocker arms are forced to follow the centre cam lobe, increasing top-end performance. The crossover from low lift to high lift occurs in 0.1 seconds and is virtually undetectable to the driver.
The short block structure is the usual die cast aluminum alloy with dry iron liners. At the bottom is a forged steel crankshaft with microfinished journals pushing on short connecting rods whose caps are retained by integral studs instead of conventional nuts and bolts. Pistons are attached with full floating wrist pins for reduced slap, and incorporate an unusual contoured piston crown with a unique charge-centralizing design that maximizes volumetric efficiency.
Fuel Injection and ETC
The new Accord V6 is fitted with the latest iteration of Honda’s Programmed Multi-Port Fuel-Injection (PGM-FI) system. It’s controlled by a 32-bit microprocessor that uses inputs from sensors measuring throttle position, intake manifold pressure, coolant temperature, intake air temperature, atmospheric pressure and the oxygen content of the exhaust gases, as well as the relative positions of the camshafts and crankshaft. Based on the input it receives, the PGM-FI signals a multi-orifice injector for each cylinder. Internal feedback circuitry allows the PGM-FI to custom match its real-time operation to accommodate the specific air-fuel conditions that exist in each individual cylinder.
Another new feature of 2003 Accord’s V-6 engine is an advanced electronic throttle control (ETC) system. This system controls the throttle during transmission shifts for improved smoothness. It also allows for throttle control to be incorporated in the traction control system and integrates the cruise control function into the ETC. Key system components include an accelerator position sensor, electronically controlled throttle body, DBW driver unit, and the main electronic control unit (ECU). Honda expects to use the Accord’s ETC technology for other powerplants in the near future.
Direct Ignition, Knock Control and Exhaust Tuning
The old hot-rodder’s trick of advancing the ignition timing until the engine knocks (or a piston melts) goes high-tech in the new V-6 with a new knock sensor that more precisely determines the onset of engine knock and modifies spark timing before detonation causes damage. The system allows the engine to run with a greater amount of spark advance and a higher compression ratio than the previous V6, increasing efficiency. A compact, high-energy ignition coil positioned directly atop each plug bore in the cylinder head activates each spark plug in the new engine.
There are no cam caps so cam removal and replacement happens through the front of the heads. Compression ratio is increased from 9.4 to 1 to an even 10 to 1, and gases exit through a new low restriction exhaust system. The exhaust is unique in that there’s no manifold; the cylinder head casting incorporates a collector that dumps exhaust directly into engine-mounted primary catalytic converters for faster light off.
Major system components include two close-coupled primary catalytic converters, a secondary underfloor catalytic converter, a centrally positioned, high-flow resonator and dual rear mufflers. The resulting emissions are clean enough to certify the ’03 Accord as a LEV II Low/Ultra Low Emission Vehicle according to the U.S. EPA. A new high-flow hydroformed 2-into-1 collector pipe transfers exhaust gas to the secondary 350-cell converter and also reduces exhaust backpressure. The lower backpressure, a 30-percent drop compared to the previous Accord V6, account for 15 of the extra 40 horsepower the new V6 develops.
Mounting the V-6
Mounting the new engine uses two centre of gravity mounts underneath, with the front both hydraulically and electronically controlled. A dual mode engine side hydraulic mount is placed high on the engine connecting to the frame rail to control powertrain motion during handling maneuvers. An upper transmission mount is added high on the transmission, connecting to the frame rail, again to control powertrain motion during handling maneuvers, and serves to provide symmetry in motion control. Finally, two rubber lower transmission mounts complete the setup.
What’s the bottom line?
The new V6 engine is nearly 9 kg (20 lb.) lighter and 25 mm shorter than the 2002 version V6 it replaces. It develops 20 percent more horsepower and 7 percent more torque, using regular unleaded gasoline. Despite the output gains, the new V6 also is expected to boost estimated fuel economy numbers in the city (11.2 L/100km vs. 11.6 L/100km). More power and better economy on unleaded fuel comes at the expense of complexity, but Honda’s scheduled maintenance for the new engine is surprisingly modest. The oil change interval is 16,000 km, and the first scheduled maintenance occurs at 168,000 km, so Honda doesn’t expect the machinery to cause much trouble. As a result, it may be a while before these find their way onto independent shop hoists. Driving the car, there’s no question that both four and six cylinder engines are more than powerful enough for the mid-size Accord chassis without undue harshness or cabin noise. In fact, with 160 horsepower, the four cylinder unit is probably enough for the vast majority of Accord owners. Or smaller Acura drivers too, which brings up the question, will the new Accord poach entry-level Acura prospects? The Accord is a strong contender, and under the hood, there’s power to spare with economy and low maintenance requirements. For Honda, it should translate into sales volumes as big as the dyno numbers.