Engine Code Differences 351CJ and 351HO

[Mclinden]

Hello Mustang Maniacs
Would someone please explain differences(if any) between the 72 351CJ motor and 351HO motors? Are the blocks the same with same code? Looking to learn something here. Thanks in advance.

 

[rvrtrash]

Both are 4 bolt main blocks, but the 71 Boss and 72 HO are supposedly selected at the factory for higher Rockwell hardness ratings, as well as the crankshaft. The CJ (Code Q) is a hydraulic lifter cam and the HO (Code R) is a solid lifter cam. The HO uses an aluminum spread bore intake and Motorcraft 4300D carburetor (735cfm). The CJ is a cast iron intake and (I think) a square bore 4300 600 cfm carb. The exhaust manifolds have a 2 1/4" opening on an HO and 2" opening on a CJ. I believe those are the major differences.