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I've been trying to determine what year this block was cast, 1969 or 1970.
The date code on the back of the block is unreadable, one on the side suggests February 4 but the year digit is a blob, think it's a '9'?
This block appears to have been decked, partial VIN pretty much erased, engine build date and suffix still pretty much there, February 25.
Suffix 'JC' is a bit of a mystery, suggests a 396?
Could have been JO, JQ... both 396?
Weren't all engine build suffixes for 1970 3 characters, 1969 two characters?
The strike in 1969 began on Sept 24, 1969, didn't end until Feb 6 1970.
Does this imply no blocks were cast in this time period?
If it does, further evidence this must be a 1969 casting.
Date code area near bellhousing, unreadable?
Looks like the block was decked, partial VIN mostly erased, engine build date and suffix mostly visible.
The suffix is confusing, 'JC', which implies this was a 396?
The casting number is 3963512 which is listed as used for 427 and 454 only?
The 3963512 block was introduced in mid 1969 and carried through the introduction of the 454 in 1970. Yes, there was a long strike beginning in September 1969 but that was at the Flint, MI location. The St. Louis plant was on strike from April 9 through June 9.
The big blocks were built in Tonawanda NY. I am not aware of any strikes at that plant in 1969 and given St. Louis plant was cranking out Corvettes continuously after June, 1969, there does not appear to be any interruptions regarding these engines.
Given the location of your cast date, you have a block that was cast on Feb 4, 1970 so was built as a 454. All 1970 454 codes are 3 character, all beginning with a C. There is a JO code for a police 396 in 1969.
The 3963512 block was introduced in mid 1969 and carried through the introduction of the 454 in 1970. Yes, there was a long strike beginning in September 1969 but that was at the Flint, MI location. The St. Louis plant was on strike from April 9 through June 9.
The big blocks were built in Tonawanda NY. I am not aware of any strikes at that plant in 1969 and given St. Louis plant was cranking out Corvettes continuously after June, 1969, there does not appear to be any interruptions regarding these engines.
Given the location of your cast date, you have a block that was cast on Feb 4, 1970 so was built as a 454. All 1970 454 codes are 3 character, all beginning with a C. There is a JO code for a police 396 in 1969.
Thanks for the response. If I understand you correctly, the 512 block being introduced in mid 1969, it could not have a February 1969 date code? It has what appears to be a date code on the side. Was the date code on the side introduced in 1970?
The part of the puzzle which I find confusing is what appears to be a JC suffix, two characters. Seems to suggest a 396? Most 70 suffixes I’ve seen begin with C, three characters.
The engine build date, Feb 25, makes sense for a block cast on Feb 4.
If you’re sure the 512 block didn’t appear until mid 1969, this would mean it had to be cast in 1970 or later. Leaving the suffix as a mystery.
Did Impalas or other applications have a JC suffix?
You've provided some good info. I’m quite curious of the suffix, only piece which I can’t reconcile.
It is generally thought the 512 replaced the 270 near the middle of the production run of the 69 but there are some posts that state the 512 surfaced earlier. My 512 was cast in October 69 and the code is cast in the right rear “shelf”, opposite the 3963512 which, as you know, appears on the left rear shelf. I am of the understanding GM moved the code to just above the starter in 1970.
If you look at the usual sites that list engine codes and differential codes, 1970 brought in the 3 character sequence.
Since you state the block was decked, I would have to say all bets are off on the stampings. Not sure why anyone would select the JO code if they were restamping. I don’t believe the 512 block was used on any 396. Others can chime in here.
512 casting date was near the starter first in October '68 and then redesigned some sources say November 17, '69 to the back of the block behind distributor. Some sources indicate a March '69 casting date transition.
Either way it was first a 427 block casting and later used to build the 454's for 1970.
JC is 396 4 barrel manual transmission Chevelle or El Camino
JO is 396 TH400 Police, passenger car.
Block cast on February 4th and assembled February 25th? Seems like a long time to sit. Where was it sitting?
Is the block 4.25" or is it 4"? If it is 4" bore, it was a 1969 cast block.
Last edited by stingr69; Nov 23, 2021 at 10:39 AM.
512 casting date was near the starter first in October '68 and then redesigned some sources say November 17, '69 to the back of the block behind distributor. Some sources indicate a March '69 casting date transition.
Either way it was first a 427 block casting and later used to build the 454's for 1970.
JC is 396 4 barrel manual transmission Chevelle or El Camino
JO is 396 TH400 Police, passenger car.
Block cast on February 4th and assembled February 25th? Seems like a long time to sit. Where was it sitting?
Is the block 4.25" or is it 4"? If it is 4" bore, it was a 1969 cast block.
The bore size is 4.280, bored 30 over.
One source stated the date code was moved from the side to the rear of the block in November 1969, further evidence this is a 1969 casting.
A mystery how it got a JC suffix, could be the suffix was partially shaved when the block was milled?
If the casting year digit is either a "9" or a "0" then yes it is a "9" - Feb 1969 casting - as Feb '70 is too late to have a cast date down low on the block.
Suffix is not really important. These were made with both 2 bolt and 4 bolt mains. You don't have a cool car to match up to it so.... it is just a block now.
there is a better pic of the stamp pad in post 20 . Im certainly no expert but it sure looks like a ghost "4" behind the second 2. also in his pic the numbers dont appear to be properly lined up. and the JC now looks more like JO to me. plus there is no partial VIN.
i also believe the 512 block never used for a 396. it is only 427 or 454. your bore measurement confirms it wasnt a 396.
so add in the questionable stamp pad, with the fact JC or JO would be a 396, which seems impossible for a 512 block, especially considering you confirmed this started life as a 4.25 bore and what you have here is what appears to be a feb 69 427 block that now lives as a 454 (his other thread shows s 454 crank)
not that im saying the engine is good or bad, im just saying the stamp pad is irrelivant as to whats for sale
there is a better pic of the stamp pad in post 20 . Im certainly no expert but it sure looks like a ghost "4" behind the second 2. also in his pic the numbers dont appear to be properly lined up. and the JC now looks more like JO to me. plus there is no partial VIN.
i also believe the 512 block never used for a 396. it is only 427 or 454. your bore measurement confirms it wasnt a 396.
so add in the questionable stamp pad, with the fact JC or JO would be a 396, which seems impossible for a 512 block, especially considering you confirmed this started life as a 4.25 bore and what you have here is what appears to be a feb 69 427 block that now lives as a 454 (his other thread shows s 454 crank)
not that im saying the engine is good or bad, im just saying the stamp pad is irrelivant as to whats for sale
"here is what appears to be a feb 69 427 block that now lives as a 454 (his other thread shows s 454 crank)"
Yes, I agree, the date code on the left side and 3963512 casting number suggest it's a Feb 4 1969 casting.
Why someone would restamp that assembly date/suffix is unknown.
The location of the date code, to me, casts doubt it could be a 1970 casting.
I see this block as valuable to anyone looking for a 'numbers correct' block.
A correct casting number and date code carry a lot of points in NCRS judging, actual VIN not so much.
Or a great base for someone looking to build an old school 454.
If the casting year digit is either a "9" or a "0" then yes it is a "9" - Feb 1969 casting - as Feb '70 is too late to have a cast date down low on the block.
Suffix is not really important. These were made with both 2 bolt and 4 bolt mains. You don't have a cool car to match up to it so.... it is just a block now.
I stand corrected on my earlier post as after some additional research, I concur with stingr69 that the casting date move TO the back “shelf” in 69. Here is a pic of my early November 69 block. You have a Feb 69 block. Thanks sting69 for setting me straight!
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What year was this block cast?
