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I just bought a 1970 corvette convertible. The dad died inherited by daughter and she sold it to me and told me the engine was replaced. My engine stamped on ledge in front is MJ10400 which lead me to an engine code of a 1969 as being a 427 400hp corvette engine. the bell housing stamp is 3970010 the 9 could be an 8. Anyways could be good news for me and i got a better engine. I know that a MH engine code is the 427 390hp from a man in hemming muscle magazine who redid one. I found the MJ code in as online listing of engine codes for 1969. So is this a real 427 400hp. swap out.?? How else can i tell if it is a big block? Ok maybe not a big block but at the bell housing there is a big 2 stamped and GM on engine. So is it definitely a GM made engine?
Last edited by Neverfail123; Aug 14, 2020 at 02:51 PM.
It is also stamped at bell housing with a big 2 GM, along with the 3970010. I have seen other codes as 1 GM. Why 2 GM. There is also a casting number on the head. with GM as part of theat mumber. I believe it to be a GM motor from anotther vette. Nobody knows why it is stamped on the ledge of front of engine( passenger side) MJ10040.????? not an engine from Mexico . I am sorry i don't buy that answer.--unless you have something to base your answer. Why would you give me such an answer as to downplay my engine with nothing to back it up?
No one is trying to downplay your engine and you can believe whatever you like. The casting code 3970010 is a small block 350. Nothing special and GM produced millions of them. Based on what I’ve seen the stamp MJ indicates that it is a crate motor manufactured for General Motors in Mexico. I’m sure it’s every bit as good as any other comparable GM 350 crate motor.
look for a the numbers on the bellhousing area looking at the back of the block should be the cast number on the left (3970010) which is a small block with a std 4.0 bore sometimes machined for a 2 bolt or 4 bolt main cap. To the left you should find a dial with a clock hand within that will be the time of day. I believe the 2 could be second shift but don't quote me. the other number on the right should be the cast date of the block that should get you a rough year.(ex J185-january 18,1975).
The front number you show on the pad I do not recognize. It could be a rebuilders stamp or a replacement-some of the GM replacements I have seen will say GOODWRENCH stamped in them. along with a partial VIN.
ny other numbers around the oil filter area or what does it have for castings on the heads?
The pad in front of the passenger side head originally will have a larger font code for the assembly date/application of the engine and a separate code in a smaller font showing production year, vehicle assembly plant and a shortened derivative version of the original vehicle identification number. (Just the last digits) Typical 1970 Corvette stampings. Other vehicles/years simmilar.
The engine assembly code begins with a single letter for the engine assembly plant followed by 4 numbers indicating the month and day of engine assembly and this code ends with either 2 or 3 letter suffix that indicate the original engine application.
Your stampings do not conform to the standard so it is more difficult to pin down what you actually have.
The casting number indicates a 350 small block that was manufactured some time beginning in 1969 and up to about 1979. That is all we know so far. It could have been used in a Corvette .....or a station wagon....or a pickup truck. Anything.
curious what side is the dipstick on? can you see any other numbers on the front pad You may see a partial VIN number from that we may be able to help with what it came from
i think the MJ in the engine stamp threw the OP off as MJ in the broadcast code,if it is valid, for a 69 does mean 427... but.... a 3970010 is not a big block
is the engine orange or blue? whats the date casting code as suggested above?
they made millions of the 3970010 block, overwhelmingly non corvette and overwhelmingly 2 bolt mains and 2 barrel carb....
you have a standard 350 motor, non original to the car, although could be if that is a rebuilders stamp, very reliable transportation, but nothing special.. shine it all up, put a little money into the car and enjoy..
His stamp has "MJ" in it as a PREFIX....not as a SUFFIX, so it is not a broadcast code. Block cast date might help as would the shape of the stamp pad.
First off, welcome to the Forum! From the information you supplied, it sounds like the engine in your car is what was called a "Target Master 350", one of the first crate motors sold by GM.
The Target Master came out in the late 70's, with a list price of about $1300, but they could normally be bought for a couple hundred less. For you're $1300 you got a new 4 bolt main 350 engine with heads, valve covers, crank, cam, pistons, oil pan and flywheel, you supplied your own intake, carb, distributor, water pump and exhaust. They were originally intended to be a replacement small block for trucks (hence the 4 bolt mains), but they became very popular as a cheap replacement engine for any Chevrolet, in need of a new small block. The Target Master was basically the same engine as the late 70's L-48 350, and was said to produce up to 250 hp, when equipped with a 4 bbl carb, and 300 ft lb torque.
I'm pretty sure the first Target Masters were made in the US, using the "3970010" block, and could be identified by a 7 digit serial number that started with "MJ", in the form of "MJxxxxx". Around 81, production was moved to Mexico, and the casting number was changed to an 8 digit number ending in "036". The Mexican Target Masters could be identified by an 9 digit serial number on the pad starting with "1M" and ending with 2 letters, such as "1Mxxxx xVP". The Mexican Target Masters can also be identified by "Hecko De Mexico" cast into the rear of the block. The Mexican 036 blocks may have been 2 bolt main blocks? Around 86, the Target Master 350 was replaced by the Goodwrench 350, but it remained basically the same engine.
The "MJ" number on the early blocks, and the "1M" numbers on the later engines, were strictly a serial number and did not serve as an engine identifier, like the suffix code found on production engines.
1969 engine code
