Pontiac used the same codes on different year blocks.To differentiate them it will have to be determined what year the block is.Next to the distributor hole there is a casting number that has a letter with 2 or 3 numbers. The letter is the month of manufacture- A=Jan. B=Feb,etc. The next number or two is the day, but sometimes the factory left the first part off, i.e. 5 could mean 5,15,25.The most important is the last number,it is the year of Manufacture it is not always the model year,as most blocks are cast a few months before the car is made. In addition 1966 and earlier blocks had 2 freeze plugs on each side of the block. 1967 and newer had 3 freeze plugs per side. These blocks had 2 motor mount holes per side.Starting in 1970, most blocks were cast with 5 motor mount holes with the mounts using 2 bolts in line with 1 higher up in the middle.Some 1977 and later blocks only had 3 holes that used the newer mounts. This means you can put a 455 in about any Pontiac car with that car's motor mounts, but if you want to use a 428 block in your 1970- Firebird you'll have to modify the frame mounts or make an adapter. Starting around 1969 Pontiac cast a 2 digit year number next to the distributor also. They also cast the engine size on the sides of the block,usually in front of the motor mounts or between the freeze plugs. Around 1968 Pontiac also stamped the VIN numbers next to the timing cover about even with the timing marks on cover.These are usually covered with oil and crud, and probably hard to see.This will tell you if this is an original motor.Pontiac Engine Codes starting in '73,2nd HP # is for Dual Exhaust
1964
C.I. H.P. #'s
326 250 HP 92x,96-0
326 280 HP 94x,97-0
389 230 HP 04L,05L,08R,09R
389 235 HP 22B
389 267 HP 11H,12H
389 283 HP 10A
389 303 HP 25K,26K,27P,28P
389 306 23B,29N
389 325 78X,79J
389 330 32B,34N,33-6
389 348 76X,77J
421 320 35B,38S,43N
421 350 44B,47S,49N
1965
326 250 WP,ZN
326 285 WR,YP
389 256 WA,WB,YA,YB
389 290 WC,YC,YD
389 325 YE,YF
389 333 WE
389 335 WT,YS
389 338 WF,YG
389 360 WS,YR
421 338 HP WG,YH
421 356 WH,YJ
421 376 WJ,YK
1966
326 250 WP,WX,YN,XF
326 285 WR,YP,XG
389 256 WA,WB,YA
389 290 WC,YV,YU,YC,YD
389 325 YX,YL,YW,YF,YE
389 333 WE
389 335 WW,WT,YS,XE
389 360 WV,WS,XS,YR
1967
326 250 HP WP,WX,WC,WH
326 250 HP YO,YN,XF,YJ,XI
326 285 HP WR,XR,WK,WD
326 285 HP YP,XG,YM,XO
400 255 HP XL,XM
400 260 HP XB
400 265 HP WA,WB
400 265 HP YA,YB,YC,YD
400 290 HP XV,XU
400 293 HP XC
400 325 HP WU,WZ,WQ,WI
400 325 HP YE,YF,YT,XE,XN,XW,XX
400 333 HP WD,WE,WY,XT
400 335 HP WT,WW,YS
400 350 HP XZ,XY,XH,XJ
400 360 HP WS,WV,WR,XS,YZ,XP
428 360 HP WG,Y2,YY
428 376 HP WJ,XK,Y3,YH,Yk
1968
350 265 HP WD,WC,YN,YJ
350 320 HP WR,WK,YP,YM
400 265 HP XM,YA
400 290 HP WA,WB,YC
400 330 HP YT,YW
400 335 HP WQ,WZ,WI,XN
400 340 HP WU,XT
400 350 HP XZ,XH,YS,YZ
400 360 HP WT,WS,XS,XP
400 366 HP WY,XW
428 375 HP WG,YH
428 390 HP WJ,YK
1969
350 265 HP WC,WP,WM,WU
350 265 HP XL,YJ,XR,YN,XB,YE,YU,XS
350 325 HP WK,WN,XC,XD
350 330 HP WR,WV,XT,XU,YP
400 265 HP XM,YZ,XX,YB,YF
400 290 HP WA,WB,WD,WE,YC,YD
400 330 HP WZ,YT
400 335 HP WQ,YW
400 340 HP XZ
400 345 HP WH,XN
400 350 HP WT,WX,YS,XH
400 366 HP WS,YZ
400 370 HP WW,XP
400 375 HP WI,WY,XY,XW
428 360 HP WG,YL,YH,XE,XJ
428 370 HP WF,XF
428 390 HP WJ,WL,YK,XG
1970
350 255 HP W7,WU,X7,YU
400 265 HP XX,YB
400 290 HP WE,YD
400 330 HP XZ,XV
400 350 HP WX,WT,XH,YS
400 366 WS,YZ
400 370 WW,WH,XP,XN
455 360 HP WA,YC,YH
455 370 HP WG,XF
1971
350 250 HP WR,WU,WN,WP
350 250 HP XR,YU,YN,YP
400 265 HP WS,WX,XX,YX
400 300 HP WK,WT,YS
455 280 HP WG,YG
455 325 HP WJ,YC
455 335 HP WL,WC,YE
1972
350 160 HP WR,YU,YV,YR
400 200 HP YX,YZ,ZR,ZV,ZX
400 250 HP WK,WS,YS,YT,ZS
455 185 YH,YW
455 200 HP ZH
455 220 HP YA,YC,Y4
455 250 YD,YK
455 300 WD,WM,YB,YE
1973
350 150,175 HP XR,WV,ZB,ZD
350 150,175 HP Y2,Y7,YR,YV,ZR,ZV
350 150,175 HP WA,WC,WD,WF,WL,WN,XZ
400 170,185 HP W5,XH,XI,X3,X4
400 170,185 HP YI,YP,YX,YZ,Y4,ZK,ZX
400 200,230 HP WK,WS,WP,YN,YX,YT
400 200,230 HP Y3,ZN,ZS,XK,XN,XX
400 200,230 HP XZ,X5,YF,YG,Y6
455 215,250 HP WT,WW,ZZ,ZE,YA,YC
455 215,250 HP YD,YK,ZA,AC,XA,XE,XJ
455 215,250 HP XL,XY,XT,X7,XO,YE
455 290 ZJ,XD
455 310 Z8,X8
1974
350 155,170 HP WA,WB,AA,YA,ZA
350 155,170 HP YB,YC,ZB,YN,YP,YS
350 170,200 HP WN,WP,ZP,YN,YP,YS
400 175,190 HP AH,YH,YJ,ZH,ZJ
400 175,190 HP AD,YF,YK,ZD,ZK
400 200,225 HP WT,WR,Y3,AT,YT
400 200,225 HP YZ,ZT,AD,YL,YM,ZS
455 215,250 HP AU,YR,YU,YW,YX
455 215,250 HP YY,ZU,ZW,ZX,A4
455 215,250 HP Y4,Y6,Y9,Z4,Z6
455 290 HP W8,Y8
1975
350 155 HP YB,YA
350 175 HP WN,YN,ZP
400 170 HP YH
400 185 HP WT,YS,YT,ZT,YM
455 200 HP WX,YU,ZU,ZW
1976
350 160 HP (Early) YB,YA,YP,YR,ZX
350 160 HP (Late) XM,XP,XU,XR,XW,XX,X3,ZF,ZH
350 165 HP ZX,ZF
400 170 HP (Early) YJ,YC
400 170 HP (Late) X9,X4,XT,XY,XS,XZ,X8
400 185 HP (Early) WT,Y6,Y7,YS,YT,YY,YZ,ZA,ZK
400 185 HP (Late) WY,X7,ZJ,ZL,X6
455 200 HP WX,Y3,Y4,Z3,Z4,Y8,ZB
1977
301 135 HP WB,YW,YX,YH,YK
350 170 HP YA,YB,XB,XC,Y9
400 180 HP XH,XJ,XD,XF
400 180 HP YU,Y4,XA,Y7,XK
400 200 HP WA,Y6
1978
301 140 HP XA,XC,XL,YM
301 140 HP XD,XB,YL,YP
301 150 HP XF,XH,XU,XW
400 180 HP XJ,XK,X9,YK,YH,YS
400 180 HP YT,YJ,YR,YW,YA,YU
400 220 HP WC,X7
1979
301 135 HP PX7,PX9,PXF
301 135 HP PXH,PXP,PXR
301 150 HP PWA,PWB
301 150 HP PX4,PX6,PXL,PXN
301 150 HP PXS,PXT,PXU,PXW
400 220 HP PWH,LAST 400
