LM7 vs L33: what's the difference?

Both are Gen III 5.3 truck engines with the same bore and stroke. The L33 is the rarer, lighter aluminum-block version with more compression and its own cam.

	LM7	L33
Family	Generation III	Generation III
Years	1999–2007	2005–2007
Displacement	5.3 L (325 ci)	5.3 L (325 ci)
Power	270–295 hp	310 hp
Torque	315–335 lb-ft	335 lb-ft
Bore × stroke	3.78 × 3.622 in	3.78 × 3.622 in
Compression	9.49:1	10.00:1
Block	iron	aluminum
AFM/DOD	no	no
VVT	no	no
Direct injection	no	no
VIN 8th digit	T	B

Key differences:

• Block: LM7 iron, L33 aluminum
• Compression: LM7 9.49:1, L33 10.00:1

L33 cam (from our engine table): Unique cam (not shared): @.050 193° duration, .482 in lift, 116° LSA. LM7 cam: 190/191 duration, .466/.457 lift, 114 LSA, 112/116 timing.

The L33 used 799-casting heads, described as "identical to 243 castings" but without the LS6-spec springs and lightweight valves — see the heads guide.

Specs are GM ratings as published; power varied by year and vehicle. Confirm any engine by the RPO code on the glovebox/console sticker.