Chevy Small Block Cylinder Head Identification Guide
Key Cast Marks Cast Nos. Description
A Rectangle 460 ‘55 & up 265/283 low comp (8:1) 1.72/1.50 valves
B Narrow triangle over rectangle 520, 896 ‘58 & up 283 PowerPak/’57-’60 Fuel Inj.,9.25:1 CR, 1.72/1.50 valves, 59cc chamber; could be good replacement on late 305 but no accessory bosses.
C Vertical bar over rectangle 997 ‘57 Corvette 270HP, 9.5:1 CR, chamber similar to PowerPak but with sharp corners in plug shroud area
D 2 vert bars over rect 997 ‘56 Corvette 2X4 bbl, 283; ‘58 pass car FI; chamber same as ‘57 270HP Corvette
E, F Large “camel humps” 291, 461, 461X, 462 Original hi-perf or “fuelie” heads; chamber sizes are 62-64cc; both 1.94/1.50 & 2.02/1.60 valve versions available; 291 on 327’s thr ‘68; 291 have temp sender hole; 462 don't
G Left-facing right triangle 041 ‘69-’70 350/300HP, accessory bolt holes, most have 1.94/1.50 valves
H Small “camel humps” 186, 492 Later hi-perf or “fuelie” heads, some 186 (‘69 & later) & all 492 have accessory bolt holes; 1.94/1.50 or 2.02/1.60 valves; 64cc chambers; ‘70 LT1/Z28 use 492; avail as PN3987376
I Large triangle over rectangle (“crown”) 882 Large chamber (76cc), hardened exhaust valve seats, compromised intake port(‘71-’76 350/400cid), best of lightweight heads
J NONE 113 ‘86-’90 Corvette/ present 350-HO aluminum, no exhaust heat, 58cc chamber, 1.94/1.50 valves, centerbolt valve covers; good street head, ‘88-on have raised D ex port, 3/8 screw-in studs
K 3 right-facing “stairs” (“bench” on intake runner) 487 ‘71-’76 76cc, best large-chamber head; 1.94/1.50 & 2.02/1.60 valves available; latter machined for screw-in studs & guideplates
L Right-facing “bench” 993 Common big-chamber head, not a lightweight casting; sim to 487; may have steam holes
M One triangle 882 Alternative marking for 882; see I, above
N 2 triangles 624 Late-model lightweight casting version of 882
O “Saddle” and vertical bar 416 Late-model 305, conventional valve covers, intake port not restricted; lightweight; 57cc chamb
P Double (Captain’s) bars 193 Mid-’80’s style centerbolt cover with restrictive vane cast in intake port (hi-swirl); not recommended for high-performance applications

Top Ten Production CSB Cylinder Heads
Also Borrowed from CAR CRAFT Magazine
No’s 1-6 are small-chamber, hi-comp and must have dished pistons to get comp below 10.5:1. No’s 1-7 have nonhardened exhaust valve seats which must be replaced for use with unleaded fuel.
Rank Cast # Good Points Bad Points
1 3782461X Hi comp (57.5cc), best ports of any OEM production cast-iron head, intake runner vol 170-180cc No accessory bolt holes, rare, likely to be cracked, 2.02/1.60 versions very rare
2 3991492 ‘70 hi-comp (61.2cc), good ports, acc bolt holes, 2.02/1.60 valve versions have screw-in studs & gplates Close proximity of water jacket to spring pocket on 492s cast prior to 1972 req special seat cutter if using larger springs
3 3890462 Ports similar to 461, but better comb chamber shape More common than 461-461X, but still rare; no acc bolt holes
4 3782461 Similar to 461X but with smaller intake ports Rare, probably cracked, no acc bolt holes
5 3927186 ‘64-’70, av chamb vol 64cc, ‘69-’70 have acc bolt holes Rare, valvespring seats close to water jackets
6 3947041 ‘69 350/300 HP, good chamb (similar to 462), acc bolt holes Very rare, valvespring seats close to water jacket
7 3932441 ‘69-’70, large chambers (73cc), some have steam holes for 400 blocks, ports decent, accessory bolt holes No 2.02/1.60 valve versions from factory
8 3973487 ‘71, 76cc, like 441 but better chamb, hard seats, acc bolt holes Big chamb needs domed pistons to get hi-comp
9 3998993 ‘71-’76 US/ ‘85-’88 Mexico, similar to 487, widely available Big chamb needs domed pistons to get hi-comp
10 332882 ‘71-’76, 350/400, big chamb, acc bolt holes, hard seats Changed intake ports, become worse, BEST of the worst
11 462624 ‘76-’78, 305, 58cc chamb, 1.84/1.50 valves, hardened seats, accessory bolt holes, best of the 305 heads 1.84/1.50 valves and ports too small for large cid; accepts 1.94/1.60 valves & seats
Casting no’s. & Date codes are cast on top of head (under valve cover) between second & third rocker arms from left.
First letter (A through M) is month (Jan through Dec)(I not used), one or two digits for day of month, one digit for last digit of year cast.
Lightweight castings (not for hi-perf use) have “scalloped” edge below exhaust ports; regular have straight edge