LS1 vs LS3: what's the difference?

	LS1	LS3
Displacement	5.7 L (346 ci)	6.2 L (376 ci)
Bore × stroke	3.898 × 3.622 in	4.065 × 3.622 in
Power / torque	295–382 hp / 323–376 lb-ft	425–436 hp / 424–428 lb-ft
Compression	10.25:1	10.70:1
Years	1997–2005	2008–2017
Heads	Cathedral-port (241; 2001+ got the LS6 intake)	Rectangle-port (L92-sourced)
Crank reluctor	24x	58x

Both have aluminum blocks. The LS3 adds a 14 mm-lift cam, 6 mm offset intake rockers, 55 mm intake valves, a high-flow intake and 47 lb/hr injectors. Swap-wise, the LS3 needs a 58x-compatible ECU/harness and rectangle-port intake; LS1 parts are cheaper and more common.