Small Block Motor Identification
Thread Starter
7th Gear
Joined: Jun 2014
Posts: 7
Likes: 0
From: Phoenix Arizona
Small Block Motor Identification
Hi Everyone,
I have looked all over the net to decipher my 350. I made an impulse buy, bad move, buying this car, but we can only go forward right ?
I have a 1974 Convertible 4 Speed with hardtop, sadly the motor
is not original. The Casting is 3970014 with cast A / 78 date.
the stamping is TG129CMJ, this is the problem.
I know the T is for Tonawanda the G I can find no reference for
as a stamping letter. As a cast letter it is July. That would
make the build date July 12 1979. That seems to make sense with a cast date of January 1978 but I can only find CMJ in the 74 and 75 years on the charts. This motor had to be built after that. It has 2 bolt mains and has been bored .030 over. I will keep looking for info, but would like to know if anyone has any thoughts or knowledge about the CMJ suffix and years it was used. I would like to know what this motor came out of. The previous owner had no knowledge. Thanks
I have looked all over the net to decipher my 350. I made an impulse buy, bad move, buying this car, but we can only go forward right ?
I have a 1974 Convertible 4 Speed with hardtop, sadly the motor
is not original. The Casting is 3970014 with cast A / 78 date.
the stamping is TG129CMJ, this is the problem.
I know the T is for Tonawanda the G I can find no reference for
as a stamping letter. As a cast letter it is July. That would
make the build date July 12 1979. That seems to make sense with a cast date of January 1978 but I can only find CMJ in the 74 and 75 years on the charts. This motor had to be built after that. It has 2 bolt mains and has been bored .030 over. I will keep looking for info, but would like to know if anyone has any thoughts or knowledge about the CMJ suffix and years it was used. I would like to know what this motor came out of. The previous owner had no knowledge. Thanks
Last edited by SgtE5; Jan 23, 2015 at 07:25 PM.
Safety Car
Joined: Dec 2012
Posts: 3,789
Likes: 1,693
From: Summerville SC
http://nastyz28.com/gm-chevy-codes/c...s-suffix-2.phpLooking at this site it's either a 400 police engine from 1974 or a 1980 305 from a camaro. If that's the case it seems like you have a nice car to start with. Start saving some money for an engine to go with it. And that thread will open the flodgates of horsepower and cubic inches. Welcome to the club.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I can find no SBC with a casting number of 3940014. It's probably 3970014.
'A78' casting is missing a character to be a valid Tonawanda date code.
TG129CMJ is probably T0129CMJ which is an engine assembled January 29, year as yet unknown.
There is no CMJ code in 1977 or '78
'A78' casting is missing a character to be a valid Tonawanda date code.
TG129CMJ is probably T0129CMJ which is an engine assembled January 29, year as yet unknown.
There is no CMJ code in 1977 or '78
Melting Slicks
Joined: Jul 2009
Posts: 2,091
Likes: 40
Not to worry.
If you had been all that interested in a car with an original drivetrain , you d put more effort into the job.
So .....it must not be all that important . Obviously not at all necessary for you to enjoy the car .
Four speed convertible . Is a lot of fun period.
Congrats....enjoy your new car .
If you had been all that interested in a car with an original drivetrain , you d put more effort into the job.
So .....it must not be all that important . Obviously not at all necessary for you to enjoy the car .
Four speed convertible . Is a lot of fun period.
Congrats....enjoy your new car .
Thread Starter
7th Gear
Joined: Jun 2014
Posts: 7
Likes: 0
From: Phoenix Arizona
I can find no SBC with a casting number of 3940014. It's probably 3970014.
'A78' casting is missing a character to be a valid Tonawanda date code.
TG129CMJ is probably T0129CMJ which is an engine assembled January 29, year as yet unknown.
There is no CMJ code in 1977 or '78
'A78' casting is missing a character to be a valid Tonawanda date code.
TG129CMJ is probably T0129CMJ which is an engine assembled January 29, year as yet unknown.
There is no CMJ code in 1977 or '78
have clear pics the Letter after the T is a G no question, that's why I assumed july 12 79
Thread Starter
7th Gear
Joined: Jun 2014
Posts: 7
Likes: 0
From: Phoenix Arizona
Not to worry.
If you had been all that interested in a car with an original drivetrain , you d put more effort into the job.
So .....it must not be all that important . Obviously not at all necessary for you to enjoy the car .
Four speed convertible . Is a lot of fun period.
Congrats....enjoy your new car .
If you had been all that interested in a car with an original drivetrain , you d put more effort into the job.
So .....it must not be all that important . Obviously not at all necessary for you to enjoy the car .
Four speed convertible . Is a lot of fun period.
Congrats....enjoy your new car .
Melting Slicks
Joined: Jul 2009
Posts: 2,091
Likes: 40
In take has raised cast numbers , and date to .
Maybe some of the other engine components were transferred to this block , ......so really even if you can read the block stamp on the pad .....it might have been rebuilt with entirely different set of components .
Looking at the individual part s and ID them could give you a ruff idea of what you have . Internals require taking engine apart .
You can check the carb ID codes. ....
Each item might add a clue to why and what happened
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
GM engine stamp pad codes were standardized in the 60s as one letter for the engine plant, followed by four digits for the month and day of the month, followed by two or three letters for the engine build type.
Never seen an engine pad with two letters for the engine plant or a letter used for the month.
Can you post a pic?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Your casting 3970014
Year Number CI HP HP Application
1970-73 3970014 350 200 300 LA built Camaro
This casting was used in 1970-1973 only. LA built Camaro only. CNJ was a 1970 350 300 HP Camaro code. Sure it isn't CNJ?
Year Number CI HP HP Application
1970-73 3970014 350 200 300 LA built Camaro
This casting was used in 1970-1973 only. LA built Camaro only. CNJ was a 1970 350 300 HP Camaro code. Sure it isn't CNJ?