Identifying 421 vs 421SD -- 66 Catalina -- which one?

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robmiller

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Based on my engine markings (behind the distributor "A205" and on the passenger side "YJ") With the PCV valve at the rear, this makes the vehicle 1965 or earlier so the date code indicates a 1965 engine and I've identified my engine as a 356HP 421, originally with a tripower setup. See this page for reference on engine codes. My question is, how do I know whether my engine is the Super Duty? I see a 356 and a 376 with codes "YJ" and "YK" -- is that the distinguishing feature, or were all of the tripowers SD motors and there's something else accounting for the difference in HP?
 
The horsepower rating for the YJ code is 356 so it is not a SD. The SD's were tripower. The SD's in 65 used an 068 cam, your's uses the 067 cam.
I use Wallace Racing for all my code look ups, head, block, etc.

Wallace Racing - Engine Code Charts

www.wallaceracing.com
 
Your chart seems superior -- a little more comprehensive -- so code YJ does show to be a tripower just not the SD. Rats. Interesting that there is a 376HP 421 4-bolt main that is listed as an HO, and also one that is not.
 
melsg5 said:
The horsepower rating for the YJ code is 356 so it is not a SD. The SD's were tripower. The SD's in 65 used an 068 cam, your's uses the 067 cam.
I use Wallace Racing for all my code look ups, head, block, etc.

Wallace Racing - Engine Code Charts

www.wallaceracing.com
Click to expand...
Also interesting that your chart also has an inconsistency. Compare the 1965 421 code YJ to the 1966 421 code YJ. 1965 shows a four bolt main but 1966 does not. Mine was built A205 = January 1965 -- if the chart is correct it is still a four bolt.
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If you use their engine code search and input 65 or 66 with YJ, they have two different block casting numbers which may explain 2 vs 4 bolt main.
 
Interesting. Thanks for the tip! Would be pretty nice to find it's a four bolt...
 
melsg5 said:
If you use their engine code search and input 65 or 66 with YJ, they have two different block casting numbers which may explain 2 vs 4 bolt main.
Click to expand...
Lots of conflicting info out there... the Wallace Racing list you sent also shows this engine as having 093 heads. I'm seeing a lot of posts indicating ONLY the 389/421 SD motors had 093 heads.
robmiller said:
Interesting. Thanks for the tip! Would be pretty nice to find it's a four bolt...
Click to expand...
Well, after all that I finally found time to crawl under this thing and lo and behold, it’s a ‘75 400 with an early style valley pan. Rats.
 
Did you find the block casting number to confirm the 1975?
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I have been unable to get to the casting on the passenger side at the back but there is a serial # stamped next to the YJ on the front. 40425B5D-53D6-47E3-B740-77E4B376EE7D.jpeg
 
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