I stumbled upon this vin code card but I'm not sure if it explains anything.
LQ9 and LQ4 are identical, except for the pistons. The LQ9 has flat top piston to reach 10.4 or so CR, while the LQ4 has dished pistons to reach 9.5 CR. Both use the same heads, 317 with 76cc chambers (which flow similarly to LS6 243 heads). The bore is 4.00" and the stroke is the same as an LS1 3.89". For a boosted application, you would be better served using the LQ4, unless you are staying at 4-6 PSI (then you can go with the LQ9).
LQ4 compression 9.4
LQ9 compression 10.0
both have 72cc heads
Vortec 6000 (LQ4)
Displacement (cu in / cc):
364 / 5967
Horsepower (hp / kw @ rpm):
325 / 242 @5200 RPMs
Torque (lb-ft / Nm @ rpm):
365 / 495 @4000 RPMs
The below pertains to the 1500HD Crews and the 2500HD Silverados/Sierras
The Vortec 6000 6.0L V-8 produces 300 hp (224 kw) and 360 lb.-ft. (488 Nm) of torque. LQ4
The Vortec 6000, or LQ4, is a V8 truck engine. It is a bored version of the Vortec 5300. Displacement is 6.0 L (5967 cc) from 101.6 mm bore and 92 mm stroke. It is an iron/aluminum design and produces 300-325 hp (224-242 kW) and 360-370 ft·lbf (488-502 N·m). LQ4s are built in Romulus, Michigan and Silao, Mexico.
Chevrolet Express/GMC Savana
Chevrolet Silverado 3500 Pickup, Crew Cab, and Chassis Cab/GMC Sierra 2500 HD Pickup and Crew Cab, Denali, and 3500 Pickup and Chassis Cab, 1500HD Crew Cab
Chevrolet Suburban/GMC Yukon XL Denali
Hummer H2 SUT
GMC Yukon Denali
 HO 6000
The Vortec HO 6000 or VortecMAX, technically the LQ9, is a special high-output version of the Vortec 6000 V8 truck engine originally designed for Cadillac. This engine was introduced in other truck lines as VortecMAX for 2006. It features high-compression (10:1) flat-top pistons for an extra 10 hp and 10 ft·lbf, bringing output to 345 hp (257 kW) and 380 ft·lbf (515 N·m). LQ9s are built only in Romulus, Michigan.
2002-2005 Cadillac Escalade
2002-2005 Cadillac Escalade EXT
2003-2005 Cadillac Escalade ESV
2003-2005 Chevrolet Silverado SS
2004-2005 Chevrolet Silverado and GMC Sierra Vortec HO Edition Only [Badging on truck]
2006-2007 Chevrolet Silverado and GMC Sierra VortecMAX Option
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