LQ4 vs LQ9: what's the difference?

Both are 6.0 L (364 ci) iron-block Gen III truck engines with the same 4.000 in bore and 3.622 in stroke. The differences:

	LQ4	LQ9
Years	1999–2008	2002–2007
Power	300–335 hp	345 hp
Torque	355–375 lb-ft	380 lb-ft
Compression	9.40:1	10.00:1
VIN 8th (truck)	U	N
Typical donors	Silverado/Sierra 1500HD/2500/2500HD/3500, Suburban 2500	Cadillac Escalade (AWD/2WD/EXT/ESV), Silverado SS, GMC Sierra Denali

The LQ9's higher compression (10.00:1 vs 9.40:1) accounts for much of its extra power. Early LQ4s (1999–2000) had iron heads. Both are common, inexpensive swap engines.