The LQ4 was a third-generation, six-liter Vortec production engine used in light-duty General Motors trucks, SUVs and vans from 1999 to 2007. "LQ4" is an RPO, which stands for "regular production order." This acronym is used to identify the engine model.
The LQ4 engine was configured in a 90-degree "V," with two banks of four cylinders spread 90 degrees apart. It had overhead valves operated by rocker arms, pushrods and a hydraulic roller-tappet camshaft. Later versions of this engine used aluminum cylinder heads, while earlier ones had cast-iron heads. These engines used electronic fuel injection and coil-near-plug ignition systems that were electronically controlled.
The LQ4 had a cylinder bore of four inches and crankshaft stroke of 3.62 inches, and its compression ratio was 9.4 to 1. The bore is the diameter of each cylinder, and the stroke is the distance the piston travels within the bore.
The LQ4 had a power output rating of 300 horsepower at 4,400 revolutions per minute (rpm) and 360 ft-lbs. of torque at 4,000 rpm.
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