The GM small-block was specifically designed as a compact sized engine to embrace the economical use of iron, and to streamline the production process. Part of the design process that was carried through to the Gen-III design in 1997, was to create lightweight rocker arms for higher RPM operation, wedge combustion chambers for a broader power band, and deliver 4.4-inch bore centers (from the center of one bore to the center of the next bore). The first small-block with a 4-inch bore came in the ’62 Corvette 327, and it really opened eyes. Featuring the famous double hump marking on the ends of the heads, the #3782461 and #3782461X heads used 1.94/1.50 inch valves. These were commonly called “Fuelie” heads because they were released with mechanical Rochester fuel injection on the stock engines. The only difference between the two casting numbers was that the #3782461 featured 160cc intake port, 62cc exhaust port and the #3782461X had the larger 172cc intake port, 64cc exhaust port. head Casting numbers on the Gen-1 cylinder heads are cast in the heads where the rocker arms and valve springs do their work. The double hump heads continued to be a favorite with performance minded enthusiasts into the new millennium. High-performance enthusiasts separated the stock Gen-I heads into closed chamber and open chamber heads. By far, the closed chamber factory heads were favored over the open chamber for making power due to the poor burn characteristics and no swirl (quench) inside the combustion chamber of the open chamber heads. Chevrolet Performance LS3 Cylinder Head Chevrolet Performance LS3 Cylinder Head small-block Chevy LS Cylinder Heads by Casting Number 10215339 – LS small-block V8 1997 346, LS1, aluminum, 68cc chambers 12480005 – LS small-block V8 2000 LS1, GTZ, aluminum, 38cc chambers, 2.125/1.625 valves, angle plugs 12556743 – LS small-block V8 1999 325, 5.3L, aluminum, truck, van 12558806 – LS small-block V8 1997-1998 346, LS1, aluminum, 68cc chambers 12559853 – LS small-block V8 1999 346, LS1, aluminum, 68cc chambers 12559862 – LS small-block V8 1999-2000 aluminum, LS, 4.8 or 5.3L 12559895 – LS small-block V8 2000 325 (5.3L) aluminum 12561706 – LS small-block V8 2001-2004 325 (5.3L) aluminum 12561873 – LS small-block V8 1999-2001 364, 6.0L, LS, 71cc chambers, cast iron 12562317 – LS small-block V8 2001-2004 364, 6.0L, LS, 71cc chambers, aluminum 12564241 – LS small-block V8 2000 346, LS1, aluminum, 68cc chambers 12564243 – LS small-block V8 2001 346 (5.7L LS6) or 364 (6.0L LS2), aluminum 12572035 – LS small-block V8 2001-2004 364, 6.0L, LS, aluminum, 71cc chambers 12550592 – LS small-block V8 1997-up 346, LS1 12559846 – LS small-block V8 1998-up 346, LS1 12560621 – LS small-block V8 1998-up 346, LS1 12562174 – LS small-block V8 1998-up 346, LS1 LT1 small-block V8 cylinder head, casting number 10125320. 10106178 – LT small-block V8 1990 350, LT5, Corvette ZR1, DOHC 32-valve, aluminum, passenger-side head 10106179 – LT small-block V8 1990 350, LT5, Corvette ZR1, DOHC 32-valve, aluminum, driver-side head 10125320 – LT small-block V8 1994-1996 350, LT1, cast-iron, Caprice 9C1 Police, Impala SS, Cadillac Fleetwood, Buick Roadmaster, reverse-flow cooling 10128374 – LT small-block V8 1992 350, LT1, 53cc chambers, angle plugs, aluminum, reverse-flow cooling, 175cc intake ports, 68cc exhaust ports 10174389 – LT small-block V8 1991-1995 350, LT5, Corvette ZR1, DOHC 32-valve, driver side, aluminum 10174390 – LT small-block V8 1991-1995 350, LT5, Corvette ZR1, DOHC 32-valve, passenger side, aluminum 10205245 – LT small-block V8 1993 350, LT1, aluminum, reverse flow cooling, 175cc intake ports, 68cc exhaust ports 10207643 – LT small-block V8 1994-1996 350, LT1, aluminum, reverse-flow cooling, 175cc intake ports, 68cc exhaust ports 10208890 – LT small-block V8 1994-1996 265, Baby LT1, L99, cast iron, reverse flow cooling 10225121 – LT small-block V8 1994-1995 350, LT5, Corvette ZR1, DOHC 32-valve, drivers side, aluminum 10225122 – LT small-block V8 1995 350, LT5, Corvette ZR1, DOHC 32-valve, passenger side, aluminum 10239902 – LT small-block V8 1996 350, LT4, aluminum, reverse-flow cooling, 195cc intake ports, 54cc chamber, angle plugs 12529742 – LT small-block V8 1995-1996 265, Baby LT1, L99, cast iron 12551561 – LT small-block V8 1996 350, LT1, aluminum, reverse-flow cooling 12554290 – LT small-block V8 1994-1996 350, LT1, Caprice 9C1 Police, Impala SS, Cadillac Fleetwood, Buick Roadmaster, reverse flow cooling 12554291 – LT small-block V8 1995-1996 265, Baby LT1, L99, cast iron 12555690 – LT small-block V8 1996 350, LT4, aluminum, reverse-flow cooling 14088526 – LT small-block V8 350, LT1, aluminum Small-Block Chevy Gen-I Cylinder Heads by Casting Number 10033867 – V8 aluminum, Pontiac 23 degree head, 62cc chambers, angle plugs, 196cc intake ports the famous double hump marking on the ends of the heads, the #3782461 and #3782461X heads used 1.94/1.50 inch valves. These were commonly called “Fuelie” heads because they were released with mechanical Rochester fuel injection on the stock engines. The famous double hump cylinder heads, the #3782461 and #3782461X used 1.94/1.50-inch valves. These were commonly called “Fuelie” heads because they were released with mechanical Rochester fuel injection on the stock engines. 10045434 – V8 aluminum, Pontiac 15 degree head, 55cc chambers, angle plugs, raised runners 10051101 – V8 Bowtie, aluminum, 55cc chambers, angle plugs, raised runners, 196cc intake ports 10065202 – 1987-1995 350, truck 10065203 – 1987-1995 350, truck 10065204 – 1987-1995 350 10065205 – 1987-1995 305 10065206 – 1987-1995 350 10065207 – 1987-1995 305 10088113 – SBC350, Aluminum, 58cc, angle plugs, raised runners, d-port exhaust, 1.94/1.5 valves 10093328 – V8 Pontiac 15 degree head, aluminum, 224cc intake ports, 61cc chambers 10110810 – 1991 350, 65cc chambers 10120928 – 1987-1995 350 10134352 – V8 Bowtie, 45cc chambers, angle plugs, low port, 223cc intake ports, aluminum, 18 degree race head 10134363 – V8 Aluminum, 18 degree or 15 degree, Bowtie race head. 10147898 – 1995-1998 350, crate engine 10159550 – 1987-1995 350 10159551 – 1987-1995 305 10159552 – 1987-1995 350 10159553 – 1987-1995 305 10185040 – V8 Bowtie, aluminum, 45cc chambers, symmetrical ports, 263cc intake ports, splayed valves 10185040 – V8 Bowtie, aluminum, 45cc chambers, symmetrical ports, 240cc intake ports, splayed valves 10239906 – 1996 350, Vortec 5700, L31, 64cc chambers, 170cc intake ports, 1.94/1.5 valves 12367712 – 1999 Fast Burn, aluminum, 210cc intake ports, port, 2.00/1.55 valves, 62cc chambers 12367713 – 1999 ZZ430 crate engine, aluminum, 210cc intake port, 2.00/1.55 valves, 62cc chambers 12480011 – 1997 Bowtie SB2.2, aluminum 12506450 – 1987-1995 350 12509859 – 1987-1994 305 12516852 – 1987-1995 350 Casting number 25534421. Casting number 25534421. 12552520 – 1997 305, Vortec, truck 12558059 – 1997 305, Vortec, truck, 1.84/1.5 valves 12558062 – 1998 350, L31 Vortec, truck, 64cc chambers, 1.94/1.5 valves, 170cc intake ports 14008856 – 1979-1981 267 14010201 – 1982-1985 305 14010516 – 1980-1986 350 14011034 – V8 Bow Tie, cast iron, 64cc chambers, 184cc intake ports, angle plugs 14011049 – Bow Tie, aluminum, 55cc chambers, angle plugs, 180cc intake ports 14011083 – 1955-1986 350, crate engine, 285hp or 300hp, 64cc chambers, 1.94/1.5 valves 14014415 – 1980-1985 267 or 305 14014416 – 1980-1986 305, 1.84/1.5 valves, 58cc chambers 14014440 – 1980 305, 1.84/1.5 valves 14019821 – 1980-1986 350 14019924 – 1979-1981 267 14019926 – 1980-1986 350 14020517 – 1980 350 14020555 – 1981 305 14020556 – 1981 350 14022056 – 1985 350 14022206 – 1980 350 14022301 – 1980-1986 305 14022601 – 1980-1986 267 or 305, 1.72/1.5 or 1.84/1.5 valves, 53cc chambers 14022801 – 1980-1986 305 14024816 – 350, 76cc chambers, 1.94/1.5 valves, crate engines 14034806 – 1978-1982 267 14034807 – 1978-1986 305 14034808 – 1980-1986 350 14034808 – 1996 350, 76cc chambers, 1.94/1.5 valves, Goodwrench crate engines 14034810 – 1980-1986 350, truck 14034811 – 1980-1986 350, truck 14039121 – 1981-1986 305, truck 14039122 – 1981-1986 305, truck 14071114 – 1980-1986 350 Casting number 19300955 Casting number 19300955 14075381 – 1980-1986 350, truck 14079261 – 1986 350 14085844 – 1980-1986 350, truck 14085963 – 1986 350 14089119 – 1986-1988 350 14094093 – 1986-1988 350 14096217 – 1955-1986 350, crate engine, 285hp or 300hp, 64cc chambers, 72 degree or 90 degree center intake manifold bolt angles 14101081 – 1987-1995 305 14101083 – 1987 350, crate engines, 285hp or 300 hp, 64cc chambers, 72 degree center manifold bolt angles 14101128 – 1986-1987 350, aluminum, 58cc chambers, angle plugs 14102187 – 1987-1991 305, 1.84/1.5 valves 14102191 – 1987 350 14102193 – 1987 305 or 350, 1.94/1.5 valves 1816887 – 1963 283, GMC HD truck 22542525 – Dart or Olds or Chevy aluminum, 14-degree or 17-degree race head 24502559 – 1996-1997 Bowtie, SB2, 1st version, mirror ports, aluminum, 196cc port, CNC version, 280cc intake ports, 38cc chambers 25500141 – Buick or Chevy aluminum, 10 degree race head, 42cc chambers, symmetrical ports, 235cc intake ports, 2.1/1.625 valves 25534351C – 2004 Bow Tie, cast iron, Vortec, 175cc intake ports, 65cc exhaust ports, 2.00/1.55 valves 25534371C – 2004 Bow Tie, cast iron, Vortec, 206cc intake ports, 77cc exhaust ports, 2.00/1.55 valves 330545 – 1973 350, 76cc chambers, 2.02/1.60 valves 333881 – 1974-1975 350, 76cc chambers, 2.02/1.60 valves 333882 – 1974-1980 350 or 400, 76cc chambers 33417369 – 1990 350, Goodwrench crate engine, 76cc chambers 340292 – 1970 replacement, angle plugs, 64cc chambers 354434 – 1975-1979 262 or 267 or 305, 60cc chambers 358741 – 1976-1979 305 3636839 – 1955 265 3703523 – 1955 265 3713358 – 1955-1956 265 Casting number 3795896 Casting number 3795896 3713569 – 1955-1956 265 3725306 – 1956 265 3731539 – 1957 283, 283hp, mechanical fuel injection 3731544 – 1957-1961 283 3731554 – 1957-1962 283 3731556 – 1957 283, truck 3731762 – 1956 265, Corvette 3737775 – 1962-1967 283 or 327 3740997 – 1957 283, carb or fuel injection, not 283hp 3743056 – 1958 283 3743096 – 1962-1967 327, GMC Truck 3747363 – 1957-1961 283 3747460 – 1959-1967 283 or 327, 70cc chambers 3748770 – 1958 283 3748772 – 1958-1961 283 3755537 – 1957-1962 283 3755539 – 1958-1962 283 3755549 – 1957-1962 283 3755550 – 1959 283 3755585 – 1962-1967 327, GMC Truck 376445 – 1977-1985 350, 76cc chambers, small valves 376450 – 1975-1981 262 or 267 or 305. 6 or 7 exhaust-bolt holes, 60cc chambers 3767460 – 1959-1960 283 3767462 – 1962-1967 327 3767465 – 1959-1961 283 3767754 – 1959-1961 283, 60cc chambers 3767792 – 1960-1964 283 3774682 – 1960-1964 283 or 327, 70cc chambers 3774684 – 1962-1964 327, 75cc chambers 3774692 – 1958-1964 283, 60cc chambers 3782461 – 1964-1966 327, camel hump, no accessory holes, 160cc intake ports, 62cc exhaust ports, 62cc chambers head Casting number 3795896. Manufactured from 1963-1965 on 283 Cubic Inch engines. Called the “Power Pack” cylinder heads. 1.72˝ intake valves and 1.50˝ exhaust valves. 60cc Combustion Chambers. 3782461X – 1960-1963 283 or 327, camel hump,no accessory holes,larger 172cc intake ports, 64cc exhaust ports, 62cc chambers 3795896 – 1963-1965 283, 60cc chambers 3795896 – 1962-1964 327, 60cc chambers 3798996 – 1963-1967 327 3814480 – 1960-1967 283 or 327, 70cc chambers, 1.72/1.5 valves 3814482 – 1962-1967 283 or 327 or 350, 75cc chambers 3817680 – 1963-1967 283 or 327 3817681 – 1962-1967 327 3817682 – 1961-1962 283 3836839 – 1955 265 3836842 – 1957-1967 283 or 327 3837064 – 1956-1962 265 or 283 3837065 – 1955-1956 265, truck 3848720 – 1957-1958 283 3876775 – 1960-1967 283 or 327, 75cc chambers 3884520 – 1960-1967 283, 60cc chambers, some used by Studebaker 3884520 – 1962-1967 327, 60cc chambers, some used by Studebaker 3890462 – 1966-1967 302 or 327 or 350, camel hump, no accessory holes, 64cc chambers 3901068 – 1987-up 350, crate engine, 285hp, 64cc chambers 3911032 – 1968 307 or 327, 70cc chamber 3912264 – 1958-1962 283 3912265 – 1963-1964 283 3912311 – 1965-1967 327 3912313 – 1965-1967 327 3917290 – 1967-1968 307 or 327 3917291 – 1967-1968 302 or 327 or 350, camel hump, no accessory holes, 64cc chambers 3917292 – 1968 327 or 350, camel hump, 64cc chambers 3917293 – 1967-1968 307 or 327, 75cc chambers 3927185 – 1969-1976 307 or 327 or 350, 70cc chambers 3927186 – 1969-1970 302 or 350, camel hump, 64cc chambers, has accessory holes 3927187 – 1969-1970 350, camel hump, 64cc chambers, has accessory holes 3927188 – 1969 327, 74cc chambers 3927188 – 1970 307, 74cc chambers 3931633 – 1968-1973 307 3931635 – 1968-1976 350 3931638 – 1968 327, truck 3932441 – 1969-1970 350, 76cc chambers 3932441X – 1969-1970 350 or 400, 80cc chambers 3932454 – 1969-1973 307 3932454 – 1969-1979 350, truck 3946812 – 1969 350 3946813 – 1969-1979 350, truck head Casting number 12529093 3947040 – 1968 327, 64cc chambers, truck, no accessory holes 3947041 – 1969-1970 302 or 350, 64cc chambers 3947041X – 1969-1970 302 or 350, 64cc chambers, 165cc intake ports 3951598 – 1970 400, 76cc chambers 3964286 – SBC 350 3965742 – 1970 350, replacement, angle plugs 3970126 – 1967-1971 327 or 350 3973370 – 1969-1970 350, 64cc chambers, straight plugs or angle plugs 3973414 – 1970 350, LT1, 350hp or 370hp, camel hump, 64cc chambers 3973487 – 1971-1972 350, 1.94/1.5 or 2.02/1.6 valves, also 1971 350 or 330hp LT1, 75cc chambers 3973487X – 1971-1972 350, 1.94/1.5 or 2.02/1.6 valves, 75cc chambers 3973493 – 1971-1972 400, 76cc chambers 3986316 – 1971 350, 76cc chambers 3986336 – 1971 350, 76cc chambers 3986336X – 1971 350, 76cc chambers 3986339 – 1971 307 or 350, 74cc chambers 3986339X – 1971 307 or 350, 74cc chambers 3986388 – 1968-1976 307 or 350 3991492 – 1970 350, LT1, camel hump, accessory holes, 64cc chambers, straight plugs 3991492 – 1970 camel hump, 64cc, straight plugs or angle plugs 3998916 – 1972 350, 1972 350 LT1, screw in studs, 76cc chambers 3998920 – 1972-1973 350 3998991 – 1972-1973 307 or 350, 75cc chambers 3998993 – 1972-1973 307 or 350, 75cc chambers 3998993 – 350, Goodwrench crate engine, 75cc chambers 3998997 – 1972-1973 350 or 400, 76cc chambers 3998997 – 1978-1984 305 or 350, 76cc chambers 4079261 – 1975 350 458642 – 1975-1984 350, 350 462614 – 1977-1979 305, 60cc chambers 462624 – 1975-1986 350 or 400, 76cc chambers, 1.72/1.50, 1.94/1.50 or 2.02/1.60 valves 468642 – 1976 350 or 400 471513 – 1979 267 or 350 517513 – 1979 267 or 350