SERVICE REPLACEMENT HEADS
These heads are designed to be direct replacements for the heads that came standard on most 454" and 502" GM V-8 big-block engines from 1990–2000. They are perfect for replacing worn or damaged heads, and they are built with the same high
quality standards that you have come to expect from GM. Service Replacement Head Technical Notes:
• Cast iron cylinder head
• Machined for 2.18"/1.88" 3/8" stem valves
• Non-adjustable rocker design
• Rectangular1 intake ports
• Heat risers
• Will not work on Production Mark IV cylinder block A. 12562925
Bare Cast Iron Gen V & VI Cylinder Head
• Bare cast iron head
• 118cc combustion chambers
• 7/16" accessory bolt holes  12562926
Bare Cast Iron Gen V & VI Cylinder Head
• Bare cast iron head
• Machined for 2.18"/1.88" 3/8" stem valves
• 118cc combustion chambers
• 3/8" accessory bolt holes (otherwise identical to P/N 12562920)
12562920
Cast Iron Gen V & VI Cylinder Head Assembly
• Cast iron head
• Completely assembled with 2.18"/1.88" valves
• 118cc combustion chambers
• Uses P/N 12562925 bare casting This head is assembled with the following components:
14097045 Intake Valves 12360874 Valve Spring Retainer & Seal Kit
14097049 Exhaust valves 3947880 Valve Locks
14097002 Valve Springs 3875916 Valve Spring Shims BOWTIE STREET HEADS GM Performance Parts is pleased to offer our Bowtie line of high performance street heads. They come with rectangular1 or oval2 intake port configuration, thick deck surfaces, and high velocity airflow passages. These heads also offer increased machining tolerances to live up to your high performance needs. With good throttle response and mid-range torque, the Bowtie line of big-block heads are perfect for street/strip big-block fans who want good low end grunt and loads of top end power.
Bowtie Street Head Technical Notes:
• 356-T6 Aluminum
• 9/16" thick decks
• No heat risers
• Will work on Mark IV and Gen V & VI cylinder block
• 1.55" Valve spring seat diameter
• Heli-coiled 7/16" screw-in rocker stud holes
• Designed for use with 3/8" pushrods
• Available as oval and rectangle ports
• As-cast intake and exhaust ports
• Use intake gasket P/N 12366985 & bolt kit P/N 12367959
• Use head gasket P/N 12363414 for bores to 4.370" & P/N 12363413 for bores 4.470" to 4.540" (Mark IV)
• Use head gasket P/N 12363412 for bores to 4.370" & P/N 12363411 for bores 4.470" to 4.540" (Gen V & VI)
• Use Head bolt kit P/N 12367779 Oval Port Heads
12363399
Bowtie Oval Port Aluminum Cylinder Head, Bare) (not shown)
• Fully machined
• Bronze guides can be finished to 11/32" or 3/8"
• Semi-finished for 2.19"/1.88" valves
• 290cc high-velocity oval intake ports
• 110cc exhaust ports
• 110cc semi-open combustion chambers
B. 12363392
Bowtie Oval Port Aluminum Cylinder Head Assembly
• Completely assembled with 2.19"/1.88" 11/32" stem valves
• 290cc oval intake ports
• 110cc exhaust ports
• 110cc combustion chambers This head is assembled with the following components:
12366986 2.19 Intake Valves 12366990 Valve Spring Retainers
12366988 Exhaust valves 12366992 Valve Locks
12462970 Valve Springs 12495690 Valve Seals
3875916 Valve Spring Shims 3921912 Rocker Arm Studs
3860038 Pushrod Guideplates 12363390
Bowtie Oval Port Aluminum Cylinder Head Assembly
• Completely assembled with 2.25"/1.88" 11/32" stem valves
• 290cc oval intake ports
• 110cc exhaust ports
• 110cc combustion chambers This head is assembled with the following components:
12366987 2.25" Intake Valves 12366990 Valve Spring Retainers
12366988 Exhaust valves 12366992 Valve Locks
12462970 Valve Springs 12495690 Valve Seals
3875916 Valve Spring Shims 3921912 Rocker Arm Studs
3860038 Pushrod Guideplates 1Rectangular intake ports are larger in volume and designed to enhance high rpm horsepower. They are an ideal street head for those big-block enthusiasts who what more power from a street car that sees a lot of drag strip action. 2Oval intake ports are smaller in volume and designed to enhance low rpm torque. They are an ideal street head for those big-block enthusiasts who want tons of bottom and power. Bowtie Street Heads Continued
Rectangle Port Heads 12363408
Bare Bowtie Rectangular Port Aluminum Cylinder Head
This head is NHRA-legal and is a replacement for 1969 L88 cylinder heads used on 1969 Camaros and 1968–1971 Corvette big-block engines.
• Aluminum performance head
• Replacement for P/N 14011076
• Machined for 2.19"/1.88" 11/32" stem valves
• 315cc rectangular cast intake port
• 110cc exhaust port
• 118cc combustion chamber 12363410
Bowtie Rectangular Port Aluminum Cylinder Head (Bare)
• Bare aluminum performance head
• Machined for 2.19"/1.88" valves
• 300cc rectangular intake port
• 110cc exhaust port
• 118cc combustion chamber A. 12363400
Bowtie Rectangular Port Aluminum Cylinder Head Assembly
• Aluminum performance head
• Completely assembled with 2.25"/1.88" 11/32" stem valves
• 300cc rectangular intake port
• 110cc exhaust port
• 118cc combustion chamber
• Uses bare head P/N 12363410 This head is assembled with the following components:
12366987 2.25" Intake Valves 12366990 Valve Spring Retainers
12366988 Exhaust valves 12366992 Valve Locks
12462970 Valve Springs 12495690 Valve Seals
3875916 Valve Spring Shims 3921912 Rocker Arm Studs
3860038 Pushrod Guideplates B. 12499255
Bowtie 572/620 Cylinder Head Assembly
• Aluminum head assembly
• Used in the 572/620 GMPP crate engine
• Completely assembled with 2.25"/1.88" 11/32" stem valves
• Valve springs for hydraulic roller cams for up to .632" lift
• 310cc rectangular intake port
• 118cc exhaust port – raised 5/8"
• 118cc combustion chamber
• Not recommended for engines smaller than 572 cid This head is assembled with the following components:
12366987 2.25" Intake Valves 12366990 Valve Spring Retainers
88963128 Exhaust valves 12366992 Valve Locks
88963934 Valve Springs 88963936 Valve Seals
88963937 Valve Spring Shims 3921912 Rocker Arm Studs
88963935 Valve Spring Locators 3860038 Pushrod Guideplates 88961160
Bowtie 572/720R Cylinder Head Assembly (not shown)
• Aluminum racing head assembly
• Used in the 572/720R GMPP
• Completely assembled with 2.25"/1.88" 11/32" stem valves
• Mechanical roller valve springs – not for use with hydraulic roller cams
• Good to .720" valve lift
• 310cc rectangular intake port
• 118cc exhaust port – raised 5/8"
• 118cc combustion chamber
• Not recommended for engines smaller than 572 cid This head is assembled with the following components:
12366987 2.25" Intake Valves 12366990 Valve Spring Retainers
88963128 Exhaust valves 12366992 Valve Locks
88963933 Valve Springs 88963936 Valve Seals
88963937 Valve Spring Shims 3921912 Rocker Arm Studs
88963935 Valve Spring Locators 3860038 Pushrod Guideplates BOWTIE RACE HEADS There’s no question that our Bowtie line of cylinder heads are just what you need for making extreme power from your GM big-block. GM Performance Parts has added huge intake ports that are raised, larger valves, smaller combustion chambers, and even two additional head bolts to increase the clamping force on the head gaskets. The runners have been left smaller so that engine builders can modify them after purchase. If you’ve got a stroked-out, big-inch, monster big-block that needs more air, our Bowtie Racing heads are just what you are looking for.
Bowtie Race Head Technical Notes:
• 356-T6 Aluminum
• 9/16" thick decks
• No heat risers
• Will work on Mark IV cylinder block
• Heli-coiled 7/16" screw- in rocker stud holes
• As-cast intake and exhaust ports 12363425
Bowtie Racing Cylinder Head (not shown)
• Aluminum racing head
• Machined for 2.19"/1.88" valves (+.400" long required)
• 380cc rectangular intake ports—raised .100"
• 110cc exhaust port—raised .750", vanes in port floor (“W” port)
• 115cc “open chamber” combustion chamber
• Rocker cover rails raised .250"
• (2) additional head bolt holes in valley
• Pushrod guide plates P/N 3860038 must be ground for clearance
• Made from un-machined cylinder head P/N 14044876 | 
