2002 LS6 got received sodium filled exhaust valves Both have 6 bolt main bearing caps. ( 4 vertical and 2 horizontal ) Oiling system was upgraded on the LS6. With roughly 500 more RPM, a larger window at the bottom of the cylinder was added. In the picture you can see a cutaway of a LS6 block. Notice the large window cut. Both blocks use cast gray iron liners. Both bores are 99 MM ( 3.8976 in ). Cranks are the same, cast nodular iron with a stroke or 92MM ( 3.6620 in ). Both have the same displacement of 5.665 liters or 345.69 cubic inches. LS6 cranks use a different dampener with an aluminum hub that is 2.6 LBS lighter then the LS1 dampener. LS6 received a larger MAF (Mass air flow) from the 6.0 liter truck engine Compression ratio was bumped four (4) tenths to 10.5/1. This was accomplished by decreasing the chamber size of the cylinder head. Exhaust ports are different with LS6 heads. LS1 exhaust ports have an "Oval" shape. The LS6 exhaust port is " D " shaped. Both use Mahle pistons. LS6 pistons are referred to as M142 which is silicon and nickle. LS1 pistons are referred to as M124. Mahle 142 (LS6 piston) is stronger and offers less heat expansion at high temp's. Camshaft changed slightly. Still a steel billet, rifle drilled for less mass. Intake ports changed greatly from the LS1 heads to the LS6 heads. See the picture below to see the major changes in the short turn radii and port floors. Both Gen III and Gen IV engines share: 0.842-inch lifter bores Four-bolt-per-cylinder head bolt pattern 9.24-inch deck height Obviously LS6 received the LS6 intake rather then the LS1 intake. See the picture below to view how the LS6 intake carries on well past the LS1 intake. An increase in plenum volume from the LS6 intake is nets about a 10 HP increase over an LS1 intake. LS1 or LS6 block? Have some thing to add to this thread? Post it below and we can add it.