V8 Engine Block Casting Numbers - 1965 through 1972

These block castings were used in various other models of the Chevrolet lineup such as the passenger car, Chevy II/Nova, Camaro and Corvette. Only Chevelle-specific information is listed here to conserve space. Some casting numbers are NOT listed as they may have been used in other models of the Chevrolet lineup but were NOT used in the Chevelle - such as the 1965/66/67 Chevy II blocks #3790721 and 3791362.

V8 Engine Block Casting Month Codes
A - January	D - April	G - July	J - October
B - February	E - May	H - August	K - November
C - March	F - June	I - September	L - December

Date codes are the letter, 1 or 2 digits for the day, and 1 digit for the year such as J 25 7 would be October 25, 1967.

The block casting number on small block and big block Chevy V8 motors is located on a ledge found at the rear of the block, most often on the driver's side. This ledge is below the deck of the block and the ledge forms the mating surface between the block and the transmission bellhousing.

Block Number	Year	Engine	Horsepower	Notes
3849852	1964	283	195, 220	Began life with the 1963 commercial truck line and used through 1966.
3782870	1965	327	250, 300, 350⁽²⁾	During 1965 model year, #3858180 was released in some applications. All #3782870 blocks should have nodular bearing caps. On 300hp and above, they all have chamfered main bearings.
3834810	1964-1965 1966 (maybe)	283	195, 220	Used only by Tonawanda Engine assembly plant. Essentially identical to #3984852.
3849852	1965 1966	283 283	195, 220 195, 220
3855961	1966	396	325, 360	Blueprints show this to be a 2-bolt block only. Is identical to #3855977 (366 truck) except for the passenger car deck heights, cylinder wall revisions and minor casting and machining. Does not have dowel pins for locating timing chain cover. Casting date on the right lower side near the freeze plug in front of the starter. Has 'tall tower' distributor casting boss.
3855962	1965 Z-16 1966	396 396	375 360⁽¹⁾, 375	Blueprints indicate this is a 4-bolt block only. Is identical to #3855977 (366 truck) except for the passenger car deck heights, cylinder wall revisions and minor casting and machining. Block has thicker cylinder walls than #3855961. Most were cast after February 15, 1965 as that was the introduction date of the 396. Does not have dowel pins for locating timing chain cover. Casting date on the right lower side near the freeze plug in front of the starter. Has 'tall tower' distributor casting boss.
3858174	1966	327	275, 350⁽³⁾	Chevrolet shows this block being used as early as 1964 in 300+ hp applications and commercial trucks. Used interchangeably with #3858180 in some applications.
3858180	1965 1966	327 327	250, 300, 350⁽²⁾ 275, 350⁽³⁾	Used interchangeably with #3782870 but had significantly thinner cylinder walls and larger water jacket.
3892657	1967	327	275, 325	Also used as new 350 engine for Camaro.
3896944	1967	283	195	Tonawanda cast block was used only for the 1967 model year and was the last 283 design.
3896948	1967	283	195	Flint cast block.
3902406	1966 1967	396 396	360, 375 325⁽⁴⁾, 350⁽⁴⁾, 375	Used in very late 1966 and 1967 models only. Second design 396 block. Primary difference between this and the #3855961/962 block is the casting of the oil galleys. First design built in both 2-bolt and 4-bolt configurations. Does not have dowel pins for locating timing chain cover. Casting date on the right lower side near the freeze plug.
3903352	1967	327	275, 325	Used mid to late in 1967 model year.
3914636	1968	307	200	Used only in 1968
3914660	1968	327	250, 275	Identical to #3914638 except for minor interior casting at bottom of cylinder bores for rod clearance.
3914678	1968	327	250, 275	Identical to #3914636 except for minor interior casting changes to cylinder wall and water jacket sizing.
3916323	1968 (early)	396	325⁽⁴⁾, 350⁽⁴⁾, 375	Used from June of 1967 to June of 1968. First block to use spin-on filter in place of canister filters used in early Mark IV engines. Block #3935440 began replacing this block around January of 1968. Casting date on the right lower side near the freeze plug in front of the starter. Has 'tall tower' distributor casting boss.
3932386	1969	350	300	Used from August 1968 until approximately January of 1969 when replaced with 3956618. Used only as 4-bolt block.
3935440	1968 (mid/late) 1969 (early)	396 396	325⁽⁴⁾, 350⁽⁴⁾, 375 325⁽⁴⁾, 350⁽⁴⁾, 375	Used for all 396 applications from mid to late 1968 and early 1969. Production stopped approximately August of 1968 although supplies would have been used in production until exhausted. Casting date on the right lower side near the freeze plug in front of the starter. Has 'tall tower' distributor casting boss.
3955272	1969	396	325⁽⁴⁾, 350⁽⁴⁾, 375	Used from approximately September of 1968 to June of 1969. Sometime between casting dates January 7 and March 17 the casting date position was moved to rear of bellhousing flange,
3956618	1969	350	250⁽⁵⁾, 255⁽⁵⁾, 300
3956632	1969	307	200	Used only in 307 applications.
3963512	1969 1970 1971	427 454 454	425 (COPO) 360, 450 365, 425	Used in both 427 and 454 applications. Lower hp versions used 2-bolt main bearing caps while higher hp versions were 4-bolt main. block had 'high tower' distributor boss and casting date located on the side of the block until redesigned on November 17, 1969 when recast with 'short tower' distributor boss and casting date moved to bellhousing area.
3969854	1969 (late) 1970 1971 1972	396 402 402 402	325⁽⁴⁾, 350⁽⁴⁾, 375 330⁽⁴⁾, 350⁽⁴⁾, 375 300 240	Used in all 402 applications. Block has 'short tower' distributor boss and casting date is found on top of bellhousing flange near casting number.
3970010	1969 1970 1971 1972	350 350 350 350	300 250⁽⁵⁾, 300 245, 270 165, 175	First appeared in late April or early May of 1969 and used through 1975. Used in both 2- and 4-bolt configurations and varied from year to year. Chevrolet shows this block only used in 4-bolt versions in 1969.
3970020	1970 1971 1972	307 307 307	200 200 130	Used for 307 applications only.
3970024	1970 1971 1972	307 307 307	200 200 130	Used for 307 applications only. Cast at the Tonawanda Engine Plant and all #3970024 engines to date have been identified as being assembled at Tonawanda.
3999289	1972	454	270	Used only in 2-bolt main configuration and saw heavy truck usage until 1978.
3999290	1972	402	240

⁽¹⁾ It has been verified that this block was installed in some 1966 Chevelle 396/360 applications causing problems for Chevrolet Service when warranty replacements required a partial engine assembly or fitted block service replacement. If the 4-bolt 375hp assembly was used to replace the 4-bolt 360hp engine, cylinder heads from the 360hp engine would interfere with the domed pistons of the 375hp block replacement. Specific partial engine and fitted block assemblies were noted for replacements.

⁽²⁾ The 327/350hp configuration was optional in 1965 but dropped for the 1966 model year until March, 1966. It's been brought up that the overwhelming majority of casting #3782870 blocks are from the Flint, MI. engine plant and supplied by Saginaw foundry while the #3858180 was done in-house at Tonawanda, N.Y. Correspondence with 1965 Chevelle L79 owners indicate that of the engines reported, most are from the Flint engine facility. My thanks goes to Mr. Randolph for alerting me to this and Mr. Cummings for his input.

⁽³⁾ The 327/350hp configuration was reintroduced for the 1966 model year in March, 1966. Although there are engine suffix ID codes for a 1966 327/350, Chevrolet does not report any L79 options being sold in the 1966 model year.

⁽⁴⁾ In 396cid applications 325hp and 350hp versions were 2-bolt main bearing caps. High performance applications were 4-bolt main bearing caps.

⁽⁵⁾ In 350cid applications 250hp and 255hp versions were 2-bolt main bearing caps. High performance applications were 4-bolt main bearing caps.