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.

 

[MOTORCITYBADBOY]

The CJ, (I currently have 6), Boss (have 1), and all 351C-4V (I have a 70 from a Mach1 going into my 69) engines are spreadbore. The aluminum intake, as far as I can tell, is no different than the cast iron, but a crap-ton lighter..

You're right on the H.O. and Boss exhaust manifold being larger at the exits..

 

[CandyRcode]

Here you go:
Blocks Identical
Cranks Stamped D1ZX-AA with 6 brinel test punches for nodularity
Rods are cast D1ZX not D0AE. They are shot peened and 180000 psi sps bolts installed.
Pistons are forged not cast and flat tops. 9.5 rated CR
Heads are cast the same. HO are milled, drilled tapped for guide plates, studs and spring seat cups (solid lifter stuff).
Valves are single groove locks not triple groove floaters.
Springs are to accommodate the solid cam profile.
Intake manifold same as Boss 351 Aluminum D1ZX-9424-CA
Distributor has a specific ID (dual point) to HO as does the carburetor. D2ZF-JA dist, D2ZF-GA carb
Dampener is identical to Boss 351 except for a slot cut in the dampener for magnetic timing pick up. Cast D2ZX or I have seen many D1ZX with a "2" stamped over the "1"
thus the timing pointer is special to HO and it is stamped D2ZXxxx
Flywheel is Cast D1ZX. Same as B351 I assume nodularity thing.
Aluminum valve covers identical to Boss 302/351
Valve cover bolts are specific to the valve covers.
Dipstick is metered for 6 quarts. ID is specific on the stick. D1ZX-BA
oil pans are the same

I may have missed something
All HO and BOSS 351 are wide ratio 4 speed and 3.91 geared. NON AIR!

 

[Mclinden]

Excellent knowledge!!! Today I am enlightened. You are great Oracles!! Thanks so much. Any production numbers for the HO and were they Mustang specific only?

 

[Keith Williams]

Here you go:
Blocks Identical
Cranks Stamped D1ZX-AA with 6 brinel test punches for nodularity
Rods are cast D1ZX not D0AE. They are shot peened and 180000 psi sps bolts installed.
Pistons are forged not cast and flat tops. 9.5 rated CR
Heads are cast the same. HO are milled, drilled tapped for guide plates, studs and spring seat cups (solid lifter stuff).
Valves are single groove locks not triple groove floaters.
Springs are to accommodate the solid cam profile.
Intake manifold same as Boss 351 Aluminum D1ZX-9424-CA
Distributor has a specific ID (dual point) to HO as does the carburetor. D2ZF-JA dist, D2ZF-GA carb
Dampener is identical to Boss 351 except for a slot cut in the dampener for magnetic timing pick up. Cast D2ZX or I have seen many D1ZX with a "2" stamped over the "1"
thus the timing pointer is special to HO and it is stamped D2ZXxxx
Flywheel is Cast D1ZX. Same as B351 I assume nodularity thing.
Aluminum valve covers identical to Boss 302/351
Valve cover bolts are specific to the valve covers.
Dipstick is metered for 6 quarts. ID is specific on the stick. D1ZX-BA
oil pans are the same

I may have missed something
All HO and BOSS 351 are wide ratio 4 speed and 3.91 geared. NON AIR!

grweat info thanks for shareing we need more guys like you on here