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351 Cleveland History (short)

The 351 Cleveland (351C) is not related to the earlier 351 Windsor, except in cubic inches. This designation is important to avoid any form of confusion. The 351C came on the scene with 1970 model introduction topped with either 2V or 4V induction. The most important difference was the heads. Two barrel heads used "open" combustion chambers, whereas 4V heads had smaller "quench" heads to achieve a higher compression ratio. Four barrel heads also had larger valves and ports, and as you might expect, a bit hotter hydraulic cam to handle the extra breathing capability. Both of  these engines were also available in 1971 models, basically unchanged. The BOSS 351 with a solid lifter cam was introduced with the 1971 models. At mid-year (May 1971), the 351C Cobra Jet (351CJ) appeared.

'71 4V/CJ Comparison Summary

The CJ hydraulic cam has more duration and overlap than the 4V. CJ blocks also feature 4-bolt main caps. CJ heads use the "open" 2V combustion chamber design, but retain the larger valves and ports of the 4V head. 4V engines used a model 4300-A Autolite carb with a standard Holley/Autolite manifold bolt pattern. CJ engines, however use a model 4300-D Autolite carb. The "D" model carburetor features small primaries and large secondaries ... and most importantly ... a larger "spread bore " manifold bolt pattern.

'72 4V/CJ Comparison Summary

In 1972, 4V and CJ engines are identical. 1971-72 CJ engines are basically the same, except for a 4-degree retard in cam valve timing specs in 1972

1971 BOSS and 1972 "R" code Comparison Summary

The major difference is in piston and cylinder head design. 1971 BOSS engines use a "quench" combustion chamber, whereas 1972 heads are the "open" type with the 1971-size valves and ports. Both are machined for a mechanical cam valve train, (which is the chief difference between the BOSS and CJ heads that are machined for a hydraulic valve train). '72 engines use a forced flat-top piston (8.8: 1 compression ratio) while the '71 engine uses a forged pop-up piston (*11.1: 1  ratio). The '71 cam provides increased duration and overlays over the 1972 grind.

(* Some automotive literature have reported 11.3: 1 or 11.7: 1 compression ratio)

 

351 CLEVELAND ENGINE COMPARISON

"The Engine of the 1970's"

 

 

1971

1972

4V and CJ

BOSS 351

4V/CJ

“R” Code

Cylinder Block

4V-2 bolt main caps     CJ-4 bolt main caps

4 bolt main caps selected from hardness

Same as ’71 CJ

Same as ’71 Boss

Cylinder Head

 

4V-Quench chamber  -64.6-67.6 cc              -non adjustable rocker arm pedestal

CJ-Open chamber  -73.9-76.9 cc       -induction hardened exhaust valve seats. Otherwise same as 4V

4V-Quench chamber    -64.6-67.6 cc            Otherwise same as’71 4V,except rocker arm pedestal machined for mechanical camshaft

Same as ’71 CJ

Open chamber

73.9-76.9 cc

Otherwise same as ’71 Boss

Cyl. Head Gasket

4V Production composition

CJ Reintz Repa comp. For 100 ft-lb torque

Reintz special comp. For 120 ft-lb torque

Same as ’71 CJ

Same as ’71 Boss

Intake Valve

2.19” dia head    11/32” dia solid stem

Multi-grove key  Sil-Chrome No. 1

2.19” dia head 11/32” dia solid stem

Multi-grove key    Sil-Chrome No. 1

Same as ’71 CJ

Same as ’71 Boss

Exhaust Valve

1.71”dia head     11/32” dia solid stem

Multi-grove key   21-4N Steel

1.71”dia head  11/32” dia solid stem

Multi-grove key    21-4N Steel

Same as ’71 CJ

Same as ’71 Boss

Rocker Arm Stud

5/16” bolt

7/16” threaded stud

Same as ’71 CJ

Same as ’71 Boss

Rocker Arm Fulcrum

“T” shaped-non adj.

Cylindrical-adjustable

Same as ’71 CJ

Same as ’71 Boss

Rocker Arm

CJ Stamped-high strength

4V production

Stamped high strength

Same as ’71 CJ

Same as ’71 Boss

Connecting Rod

1041-H Forged Steel

3/8” nut and bolt

1041-H Forged Steel

-shot peened  and  – magnafluxed

-improved durablilty 180,000 psi 3/8”

nut and bolt

Same as ’71 CJ

Same as ’71 Boss

Piston

Cast Aluminum-flat top

CJ –   9.0:1 CR

4V – 10.7:1 CR

Forged Aluminum Pop up

11.1: 1 CR

Same as '71 CJ

Except  9.0: 1 CR

Forged Aluminum-flat top 9.2: 1 CR

Piston Pin

0.912”dia I.D.  non-tapered

0.912” dia I.D.  non-tapered

Same as ’71 CJ

Same as ’71 Boss

Con Rod Bearings

Over-plated copper/lead

W/increased eccentricity

Same as CJ

Same as ’71 CJ

Same as ’71 Boss

Oil Pan assembly

Production w/welded windage baffle

Same as CJ

Same as ’71 CJ

Same as ’71 Boss

Oil Level Indicator

Calibrated for 5 quarts

Calibrated for 6 quarts

Same as ’71 CJ

Same as ’71 Boss

Intake  Manifold

Cast Iron-over/under

Cast Aluminum-over/under

Same as ’71 CJ

Same as ’71 Boss

Carburetor

4V-Autolite Model 4300-A w/std bolt pattern

CJ-Autolite Model 4300-D

w/spread bore pattern

Autolite Model 4300-D  w/spread bore pattern

Same as ’71 CJ

Same as ’71 Boss

Except with different calibration

Distributor

4V-Single Point   Dual diaphragm

CJ-Dual Point      Dual diaphragm

Same as CJ, except for calibration

Same as ’71 CJ

Same as ’71 Boss

Rocker Arm Covers

Stamped Steel

Cast Aluminum

Same as ’71 CJ

Same as ’71 Boss

Air Cleaner

Ram-air-optional

Ram air

Ram air not available

Ram air not available

Oil    Oil Fill

5 Qt. SAE 10W-30

6 Qt. SAE 40 (summer)

6 Qt. SAE 30 (winter)

Same as ’71 CJ

Same as ’71 Boss

Rear Oil Seal

Rope type

Split lip

Same as ’71 CJ

Same as ’71 Boss

Valve Spring

285 lbs @ 1.32 open

325 lbs @ 1.32 open

Same as ’71 CJ

Same as ’71 Boss

Valve Sp. Retainer

Compatible with multi-groove keeper

Compatible with single-groove keeper

Same as ’71 CJ

Same as ’71 Boss

Valve Spring Key

Multi-groove

Single-groove-hardened

Same as ’71 CJ

Same as ’71 Boss

Valve Stem Seal

Production 351C

Production 429 with shorter skirt for improved lubrication

Same as ’71 CJ

Same as ’71 Boss

Valve Spring Seat

None required

Stamped Steel

Same as ’71 CJ

Same as ’71 Boss

Push Rod

Production

Hardened and ground

Same as ’71 CJ

Same as ’71 Boss

Push Rod Guide Plate

None required

Same as Boss 302

None required

Same as ’71 Boss

Camshaft

Hydraulic

4V-duration 266 degrees i/270 degrees E overlap 34 degrees lift 0.427”

CJ-duration 270 degrees i/290 degrees E overlap 46 degrees lift 0.480”/0.488”

 

Mechanical

Duration 29i0 degrees I and E

Overlap 58% lift 0.477”

 

Same as “71 CJ

Except valve events retarted 4 degrees

Mechanical

Duration 275 degrees I and E

Overlap 35 degrees lift 0.491”

Tappets

Hydraulic

Mechanical Internal metering

Same as ’71 CJ

Same as ’71 Boss

Crankshaft

Cast Iron

Cast iron-selected for hardness (90% nodularity)

 

Same as ’71 CJ

Same as ’71 Boss

Damper

01.10 inertia                    -cast iron hub         -cast iron inertia ring -non-bonded elastic member                     -28.2 oz-in unbalance

 

0.14 inertia               -nodular iron hub          -wider cast iron inertia ring -bonded elastic member -27.3 oz-in unbalance

Same as ’71 CJ

Same as ’71 Boss

Flywheel

Cast Iron-28.2 oz-in unbalance

 

Nodular Iron-27.3 oz-in unbalance

Same as ’71 CJ

Same as ’71 Boss


*info from Ford - February 1972

*Note: Thanks to Allen Cross www.Fomoco.com for the use of his engine icon

 

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