3418915 "J" head build date casting code

[76orangewagon]

I just picked up a set of 3418915 J heads and am having difficulty decoding the build date. They look like 2460 and 2860 or 2880, if I was guessing I'd say 2460 is the 24th of June 1970 and 2860/2880 is the 28th of June or 28th August of 1970. Can someone please help me out with what numbers are. My 71 intake has 2571 which is Feb 5th, 1971 but this four digit number doesn't work for that date sequence. Thanks in advance for any and all help. .

[GY3R/T]

 2460 could be june 24 1970 OR sept 3 1970.

[Cuda Cody]

2880 I think is the 288th day of 1970.

[kawahonda]

Curious if anyone has a magic decoder ring. J heads use both small and large valves. Is there anyway to tell what it has from the outside, such as date codes? Also, did J heads ever appear on a 1970 Challenger? Mine are painted blue which is not right, and are J heads. Curious if ALL A66 1970s should have X heads...

[76orangewagon]

2880 I think is the 288th day of 1970.

That make more sense

[340challconvert]

Cody is correct
2880 = 288th day of 1970, which was Thursday, October 15th, 1970
Those heads would have been on a 1971 model car; explains the blue paint color.
A66 code Challengers were built only in 1970.
Obviously there were 1971 340 Challengers but with no A66 code. 1971's could have been JH or JS cars.

MMCdetroit does a good job of explaining date codes; http://www.mmcdetroit.com/Understanding_Date_Codes/

[Rich G.]

My 70 Challenger is original and has J heads on it. I thought they would be X heads but they do have the big valves in them

[340challconvert]

This information I stored when I was researching Mopar small block heads may also help!

340 Heads

The '70 model 340 heads were the 'J' 915 castings and they came with 2.020 valves.
The 894 'X' castings were used on the '68 and '69 340's only.
Might have been a few very early '70 models with them but the official casting for 1970 through 1973 was the 'J' 915 castings.
The six-pac heads with the pushrod hole machined for offset rockers were 'J' 915 castings in 1970.
The first year for the 360 was 1971; they had 'J' 915 castings. The 915 castings had 2.020 intake valves in 1970 and 1971. 1972 and 1973 340's and all 360's 1971 -1973 with 'J' heads had 1.880 intake valves, as did all 360's.

[76orangewagon]

Cody is correct
2880 = 288th day of 1970, which was Thursday, October 15th, 1970
Those heads would have been on a 1971 model car; explains the blue paint color.


MMCdetroit does a good job of explaining date codes; http://www.mmcdetroit.com/Understanding_Date_Codes/

Thanks for the verification, I looked at Dave's quick reference guide and at the web site for date codes but missed the side link to the understanding date codes..