Here is several head designs GM sells

12480090
Bare C5R Racing Cylinder Head
355-T7 'as-cast' Aluminum racing head
Professional porting and machining of combustion chambers required
No seats or guides
C5R rectangle port design requires aftermarket rectangle port intake manifolds
Designed for 2.180/1.625 valves
11' valve angle
Machined for 1.625 diameter valve springs & .500 guides
Designed for big bore (4.100 min) LS7/C5R/LSX blocks
210cc 'as-cast' intake ports
70cc 'as-cast' exhaust ports, same as production LS6
30cc 'as-cast' combustion chambers
All fasteners are metric
Valve cover rails have O-ring groove for .125 O-ring
Capable of over 800 horsepower!

12564824
LS6 Cylinder Head Assembly
Fits any 1997'2008 LS Family engine*
2.00 hollow stem intake, and 1.55 sodium filled exhaust valves
.570 max valve lift
210cc 'cathedral port' intake ports
70cc D-shaped exhaust ports
65cc combustion chambers
Bare head P/N 12564825 available separately

Heads P/N 12564824, P/N 88958665 and P/N 88958622 are
assembled with the following components:
12565311 Intake Valves
10166344 Valve Spring Retainers
12565312 Exhaust Valves
12482063 Intake Valve Stem Seals
12586484 Valve Springs
12482062 Exhaust Valve Stem Seals
10166345 Valve Locks

For LS2

12576063
LS2 Cylinder Head Assembly
Lower cost alternative to the LS6 head
Fits any 1997'2008 LS family engine*
2.00 Solid stem intake, and 1.55 solid stem exhaust valves
.570 max valve lift
210cc 'cathedral port' intake ports
70cc D-shaped exhaust ports
65cc combustion chambers
Bare head P/N 12564825 available separately
Upgrade the valves to LS6 hollow stem valves with P/N 17801930

12578449
LS7 Cylinder Head Assembly
356-T6 aluminum head
Fully CNC'd ports and chambers
LS7 rectangle port design requires rectangle port intake manifold P/N 25534394, P/N 25534413 or P/N 12568976
Assembled with 2.20 titanium intake and 1.61 sodium filled exhaust valves
12' valve angle
Designed for big bore LS7/C5R/LSX blocks
(min 4.100 bore)
270cc CNC'd intake ports
85cc CNC'd exhaust ports
70cc CNC'd combustion chambers
All fasteners are metric
Capable of over 600 horsepower
Bare head P/N 12578450 available separately

25534428
LS7 Bare Unported Cylinder Head (not shown)
356-T6 aluminum head
LS7 rectangle port design requires rectangle port intake manifold P/N 25534394, P/N 25534413 or P/N 12568976
Machined for 2.20/1.61 valves
Designed for big bore LS7/C5R/LSX blocks (min 4.065 bore)
Limited availability

88958665
CNC-Ported LS6 Cylinder Head Assembly
CNC-ported aluminum performance head
Fits any 1997'2008 LS family engine*
2.00 Hollow stem intake, and 1.55 sodium filled exhaust valves.570 max valve lift
250cc CNC'd 'cathedral port' intake ports
85cc CNC'd D-shaped exhaust ports
65cc CNC'd combustion chambers

Heads P/N 12564824, P/N 88958665 and P/N 88958622 are
assembled with the following components:
12565311 Intake Valves
10166344 Valve Spring Retainers
12565312 Exhaust Valves
12482063 Intake Valve Stem Seals
12586484 Valve Springs
12482062 Exhaust Valve Stem Seals
10166345 Valve Locks

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88958622
CNC-Ported LS6 Racing Cylinder Head Assembly
CNC-ported aluminum racing head
2.00 Hollow stem intake, and 1.55 sodium filled exhaust valves
.570 max valve lift
250cc CNC'd 'cathedral port' intake ports
85cc CNC'd D-shaped exhaust ports
62cc CNC'd combustion chambers

Heads P/N 12564824, P/N 88958665 and P/N 88958622 are
assembled with the following components:
12565311 Intake Valves
10166344 Valve Spring Retainers
12565312 Exhaust Valves
12482063 Intake Valve Stem Seals
12586484 Valve Springs
12482062 Exhaust Valve Stem Seals
10166345 Valve Locks

88958698
NEW CNC-Ported L92 Cylinder Head Assembly (not shown)
CNC-ported performance head
Fits any LS family engine with a bore of 4.00 or larger
Uses stock 2.165 and 1.590 valves, springs and hardware
Stock intake and exhaust port locations
.510 max lift with stock springs
280cc intake port, 100cc D-shaped exhaust port, 68cc combustion chamber
Not compatible with LS7 intake manifolds

CNC L92 Head Flow Data (4.065 bore):
Lift 0.200 0.300 0.400 0.500 0.600
Intake 150 222 260 298 332
Exhaust 105 140 168 190 201

88958765
CNC-Ported LS2 Cylinder Head Assembly
CNC-ported aluminum performance head
Lower cost alternative to the CNC LS6 head
Fits any 1997'2008 LS family engine*
2.00 solid stem intake, and 1.55 solid stem exhaust valves
.570 max valve lift
250cc CNC'd 'cathedral port' intake ports
85cc CNC'd D-shaped exhaust ports
65cc CNC'd combustion chambers
Upgrade the valves to LS6 hollow stem valves with P/N 17801930