Seeking to reach the 50,000 trucks per year sales plateau in the US, Isuzu has completely revamped its N-series trucks in Class 3 to Class 5. Isuzu, now completely independent from any ownership relationship with General Motors, markets trucks in the US as an equal partner in General Motors Isuzu Commercial Truck LLC. The company sells vehicles under three nameplates — its own Isuzu label as well as Chevrolet and GMC.
In developing the new N-series, Isuzu consulted with customers, dealers, and body builders to ensure that the new trucks would satisfy all three constituencies. Customers reported wanting a roomier cab with more storage for driver belongings. Dealers wanted additional wheelbase options allowing the mounting of bodies up to 24 ft in length and 102 inches of width. Body builders wanted truck frames with standard hole spacing to simplify body mounting.
At the heart of the new N-series is Isuzu's 5.2-liter 4HK1-TC diesel engine. The four-cylinder engine boasts increased horsepower for the 2008 model year now on sale, up to 205 from the 190 hp rating for the 2007 models now being phased out. Torque increases as well to 441 lb/ft at 1,850 rpm, up from 387 lb/ft in the previous version. The engine covers the entire model range for weight ratings from 12,000 lb to 19,500 lb. The engine has a design life that allows 90% of engines to run 310,000 miles before any major component failure, provided that normal maintenance is performed.
To meet the strict new exhaust emission rules for oxides of nitrogen that went into effect on January 1, 2007, Isuzu engines use advanced exhaust gas recirculation and a variable geometry turbocharger. The new exhaust regulations also limit particulate emissions. To meet those requirements, Isuzu employs a ceramic honeycomb channel diesel particulate filter to capture soot and sulfate particles. The filter routes exhaust gas through channels of porous material to trap the particles. To prevent clogging, the filter runs through a periodic regeneration cycle that burns off trapped particles using high-temperature exhaust gas. The regeneration cycle can occur as a normal part of engine operation or can be initiated by the operator with a computer-controlled process.
Filter regeneration is a normal part of engine operation, unless the engine is not producing exhaust gases hot enough to clean the honeycomb. In that event, a warning lamp on the instrument panel instructs the driver to initiate the regeneration process.
While the exhaust system is designed to operate as efficiently as possible, it does present challenges to body builders. In particular, exhaust components must remain mounted in the same position throughout the life of the vehicle. Body builders are not allowed to reposition exhaust system components as a part of body mounting. In addition, the regeneration process generates additional exhaust heat. Isuzu equips the N-series with an exhaust cooler to eliminate the need for heat shields with certain body configurations.
The exhaust system affects the fuel system as well. To make room for the additional exhaust system components, Isuzu has had to reposition the fuel tank, mounting the standard 30-gallon tank between the frame rails, behind the drive axle. To ensure fuel system integrity, fuel lines run through the frame rails.
Automatic transmissions are standard equipment with the new N-series using the AISIN A465 six-speed. A six-speed, fully synchronized manual transmission is available as an option.
The N-series is the only low-cab-forward truck on the US market that can be specified with a gasoline engine. The General Motors 6-liter V-8 produces 325 hp at 5,000 rpm and is designed for a 200,000-mile service life. The engines are certified for use in all 50 states. When the premium for 2007-compliant diesel engines is factored into the cost equation, gasoline engines may enjoy a price advantage of nearly $5,000 compared to the same truck with diesel power. The GM gas engine can be modified to burn compressed natural gas. However, gas engines are not certified for ethanol use.