LQ4

• The LQ4 is referred to as the Vortec 6000 by General Motors. The engine is 366 cubic inches in displacement, with a 101.6mm bore, a 92mm stroke, a 4.0-inch bore, and a 3.622-inch stroke. The engine features 300 to 325 horsepower and 360 to 370 pound-feet of torque, depending upon the type of engine heads. (Early models were equipped with cast-iron heads.) In 2005, GM began putting the LQ9 floating wrist pin rods in the LQ4 engines, but the company utilized dished pistons instead of flat-top pistons.
  
  

LQ9

• The LQ9 is referred to as the Vortec HO 6000, or VortecMAX. It is a high-output version of the LQ4 and was introduced in 2006. The LQ9 is equipped with flat-top pistons and floating wrist pin rods. The flat-top pistons allow for an increase in compression, and the engine produces slightly more power than the LQ4 (plus-10 horsepower and plus-10 pound-feet of torque).
  
  

Visual Distinctions

• Visual identification between the two engines is very difficult, since the primary difference is the pistons and wrist pin rods, which are part of the engine's rotating assembly and thus enclosed in the engine block.
  
  

Replacement

• The LQ4 was replaced by the LY6, a General Motors Generation IV engine that incorporates variable valve timing. The LQ9 was replaced by the L76, which incorporates an all-aluminum block in addition to variable valve timing.