FORD'S ORIGINAL 351 was the Windsor, closely relatedto the 289-302's which powered many successful race

cars in far flung forms of competition. The 351W simplyhad a stroke 1/2-inch longer than the 302 and a new kindof free-flowing, big-valve head. Introduced in 1969 andreplaced by the 351 Cleveland in 1970, the 351W nevertook the racing world by storm.

Now the 351C is a new baby that is having some teethingproblems but shows great potential as a racing power-plant. In an effort to clear up some misconceptions aboutthis engine and hopefully to establish a solid foundationfrom which racers can develop it, we herewith present afew facts, figures, and part numbers. This advice is basedon research done by the factory so it should provide agood jumping off place.

The 335 series engines were introduced in the 1970model year. The factory used up the old 351 Windsorengines as 2-bbl. engines while the supply lasted. Mean-while the 351 Cleveland came out as a 4-bbl. and later a2-bbl. In '71 the 400, CJ, and Boss versions of the Cleve-land engine were introduced. Then in '72 the Boss wasrenamed the 351 H.O.

Identifying 335 series engines is not difficult. If theoriginal engine is in the body with which it left the factory,one simply scopes out the identification tag in the driver'scorner of the dashboard. The first digit represents themodel year and the fifth digit (a letter) tells which engineyou have. In descending order of desirability these are:(R) 71-72 351 Boss or H.O., (Q) '71-72 351 C.J., (M) '69-71351 4V, (H) '69-72 351 2V, (S) '71-72 400 2V. Another iden-tification tag is located under the coil and the number isalso on the front of the block.

If you're asking why the 400-inch version of the Cleve-land rates so low in our ranking it is because this strokerengine has different rod journals from the 351 C, whichlimits interchangeability of parts. It, being a 2-bbl. motor,is also blessed with two-bolt main caps. You might notethat the main and rod journals of the 400C match up withthe 351 W, so there's room for some expermentation thereif you have an old 351W block handy.

To get the most racing engine for the least trouble,start with the 351 Boss or the 351 H.O. The Boss enginewas introduced in the '71 cars and was superseded by theH.O. in '72. These are identical except for compression

by Denis Hill

351= SLEEPERCanted valves, big ports, and a strong bottom end

add up to a lot of yet unfulfilled potential for^Ford's 351 Cleveland.

ratio and combustion chamber configuration. The dif-ferences are not as great as one might think.

The '71 351 C.J., 72 351 C.J., and '72 351 4V are all thesame. These are good engines with the four-bolt mainsbut they don't have all the good parts of the Boss andH.O. Still, if you plan a complete rebuild, they'll do justas well. A warning is in order on these 4V engines: the'70 and '71 versions don't have the four-bolt mains.

All the 2-bbl. engines have smaller valves and portsthan their more heavily carbureted kin, and only the Bossand H.O. come with provision for valve lash adjustment,as the other engines all use hydraulic cams.

One of the design features that makes the Cleveland soattractive as a racing engine is the canted valve configura-tion. The valves are canted at a compound angle to theirrespective heads for improved flow. In the 4V, Boss, C.J.,and H.O. these valves are 2.19" for the intake, and 1.71"for the exhaust. The 4V and C.J. valves are designed fora multi-groove keeper which promotes rotation. Thesingle-groove keeper used in the Boss and H.O. enginesgives better control and should be used in high-rpm ap-plications. The stem diameter of these Boss valves is11/32".

The ports of the Boss, C.J., and 4V are large and oval,

ABOVE- The harmonic balancer on theleft is the one that comes with theordinary 351C. The balancer at right is theheavier and more clearly marked "Boss"model.

BELOW- The Boss 351 gets a selectedfor hardness cast crank, but an aftermarketsteel unit is recommended forsustained high-rpm applications.

RIGHT-Boss 351 rod assembly ismagnafluxed and used large, high-

strength bolts and comes with betterbearings than the ordinary 351 gets.

t. / .

LEFT— The "Boss" and other high-performance versions of the 351 C get the

four-bolt main cap while 2 bbl. enginesdo not. The timing chain housing

incorporated in the front of the Clevelandblock eliminates the need to route water

through the intake manifold.

DECEMBER

resembling the Boss 302 heads. When properly portedand polished these heads will flow 450 cfm on the intakeside and 300 cfm exhaust.

The Boss and H.O. use selected connecting rods ma-chined from SAE 1041 steel. These are shot-peened andmagnafluxed and come with 180,000 psi, %" bolts. Thewhole deal is good for 7,500 rpm.

The question of heads for a 351C engine gets com-plicated. Only the H.O. and Boss heads come set up forthe adjustable rockers by means of which valve lash isattained. However, only minor machine work is needed to

49

One of the first and perhaps biggestdecisions to attack in building a racing

351 is choice of heads. Are openchamber heads preferable to

quench heads?

351 = Sleeper

BELOW-The quench Boss heads featurethe same big valves as other 4 bbl. engines.

The ports are larger than the older head.The '71 CJ and '72 H.O. heads feature open

chambers, but are otherwise identical tothe '71 Boss head.

make the conversion (see "351 Head Job," Oct. '72 SCR).The '71 4V and Boss use the quench combustion chamber,while the '71 C.J. and all '72 engines use open chamberheads. The '71 4V has a cast aluminum flat top piston for acompression ratio of 10.7:1. The '71 Boss uses a forgedaluminum pop-up piston to achieve a c/r of 11.1:1. The72 C.J. gets a 9.0:1 out of a flat-top, and the '72 H.O. pullsa big 9.2:1 from a flat top forged piston. In short, the Bossis the only combination (quench head and pop-up piston)approaching performance.

The mechanical cam 351 's use hardened & ground pushrods with Boss 302 guide plates. The crank in theseengines is cast iron, selected for hardness, 90% nodularity.The harmonic damper and flywheel are also stronger andheavier on the Boss and H.O.

PART SELECTIONOne of the first and perhaps biggest decisions to attack

in building a racing 351 is choice of heads. Are openchamber heads preferable to quench heads? First itshould be noted that the current popularity of open-chamber heads in automobile manufacturing is due totheir ability to produce fewer pollutants. Open chambersalso promote better breathing and good top end power.Quench heads help create a swirling of the air/fuel mix-ture and give better torque. Tests of otherwise identicalengines have shown that the power-producing ability ofopen-chamber heads may be a couple of horses betterthan quench heads. This may not apply to every engine,and we don't know if it applies to the 351, but bear it inmind.

On the subject of heads, you may run across a few odd-ball heads with 2.3" intake valves. Some of these wereproduced in 1970 but they hurt in the torque department.

50 STOCK CAR RACING

Stock 351 Boss PartsPart Number Description

D1ZZ-6009-D Engine Short Block-71D1ZZ-6010-D Engine Block-71 Boss-4-bolt selected

• hardness capsD1ZZ-6049-B Cylinder Head-71D1ZZ-6051-C Gasket-Cyl. Head-71D1ZZ-6108-A Piston & Pin Assembly-71 std. red sizeD1ZZ-6108-B Piston & Pin Assembly-71 std. blue sizeC9ZZ-6135-E Piston PinD1ZZ-6200-A Connecting RodD1ZZ-6211-A Bearing-Con Rod (std. size)D1ZZ-6212-A Nut-Con Rod %"-24D1ZZ-6214-A Bolt-Con RodD1ZZ-6250-B Camshaft-Mechanical 71D1ZZ-6303-A CrankshaftD1ZZ-6316-B Damper-CrankDOAZ-6345-B Main Cap Bolts V2"-13 x 3'A"C9AZ-6345-A Main Cap Bolts %"-16353992-S Washer-Flat %"D1ZZ-6375-B Flywheel & Ring GearD1ZZ-6500-B Tappets - MechanicalDOZZ-6505-A Exhaust Valve 1.71" dia. 5.05" longDOZZ-6507-A Intake Valve 2.19" dia. 5.23" longDOZZ-6513-A Valve Spring (#4 dark blue stripes)C9ZZ-6514-A RetainerC9ZZ-6518-A KeeperC9ZZ-6A527-A Stud-Rocker Arm 7/i6"-20 (top) 7/i6"-14

(bottom)C9ZZ-6A528-A Seat-Rocker Arm Fulcrum 71C9ZZ-6A529-B Nut-Rocker StudC9ZZ-6A536-A Seat-Valve Spring (before 1-1-71)DOOZ-6A536-A Seat-Valve Spring (after 1-1-71)C9ZZ-6A564-A Guide Plate-Push RodDOOZ-6565-F Push Rod-Hardened 8.52" long (71)C9ZZ-6571-A Seal-Valve Stem 71C9ZZ-6582-C Rocker Covers-Aluminum (R.H. & L.H.)

351

Part NumberD3ZZ-6051-AD1ZX-6500-CA

DOZX-6505-A

DOZX-6507-ADOZX-6A511-A....

DOZX-6A585-A....

D2ZX-6670-A

DOAZ-9433-A

D1ZX-9425-FA

D1ZZ-9424-G

Boss "Competition Only" PartsDescription

.Gasket-Cyl. Head

.Mechanical Tappets—80.00 radius (to serviceabove kit)

.Exhaust Valve—Lightweight (95 gms.)1.71 "dia.

.Intake Valve—Titanium (85 gms.) 2.19" dia.

.Valve Spring—Three Piece (Load-130 Ibs.@1.69")

.Needle Bearing Rocker Arm Kit —Includes:bearing assy, bearing housing, nut, shaftand set screw

.Spring —Oil Pump (increase pressure to100psi)

.Gasket Kit-Int. Manifold (trim sides of steelgaskets)—351C

.Intake Manifold—4V, single plane aluminum(For Holley 4500)

.Intake Manifold —4V, dual plane aluminum(For Holley 4150-4160)

Misc. Clearances and Specs for the Ford 351CDeck clearance for TRW piston .Piston to valve clearance

Piston to deck volume TRWCombustion chamber vol. TRW.

Gasket volume (D3ZZ-6051-A)Bearing clearances main

rodcam

End play crankcam

Valves.dist. shaft

.stem to guideex.in.

lash in. & ex.

Piston to boreto pin

Ring end gap comp.oil

Ring to groove comp.oil

0.0100.100 min.I&E @ 0 lash

-8.6 cc66.1 cc (mill0.006" to re-duce vol. 1 cc)8.0 cc0.0025-0.00300.0025-0.00300.0010-0.00300.004 -0.0100.001 -0.0060.004 -0.025

0.0011-0.00220.0007-0.00180.025 hot0.025 -0.028

cold0.0065-0.00750.0006-0.00080.015 -0.0200.015 -0.0690.002 -0.004snug

Balance and Weight Information(Grams)

Bobweight (estimated)Reciprocating:

Piston 1 580

No. Required Stock TRW

510

Compression Ring (upper) 1Compression Ring (lower) 1Oil Ring 1Piston Pin (C9ZZ-6135-A) 1Conn Rod Assy (piston pin end) 1

Centrifugal:

Conn Rod Assy (crank end) 2Conn Rod Bearings 4Oil in Crankpin

Total BobweightLess Equivalent External Bobweight of

27.3 oz. in. in Damper and Flywheel

Crankshaft Bobweight

18.918.920.5

146.5194

978.8 908.8

110887.54

1199.5 1199.52178.3 2108.3

777.1 777.1

1401.2 1331.2

I

They are not generally recommended.The Boss valve measure intake 2.19, 5.23 long, exhaust

1.71, 5.05 long. The part numbers are ex. DOzz-6505-A,in. DOZZ-6507-A. If you want to lighten up the valve trainyou might go back to Hank Manley's light-weight stainlesssteel valves. The head diameters are the same as stock butthe stem measures 5h&". Obviously a valve guide sleevemust be installed with these valves. Manley recommendsthese valves to improve valve spring and camshaft life, andpoints out that the stainless valves feature a head shapethat flows a great deal better than stock, titanium, and

DECEMBER

hollow-stem valves. His intake valve weighs just 100grams, and the exhaust is a heavy 90 grams. The closematching of the weight is an added plus. The intakenumber is 11810, and the exhaust number is 11811.Manley Performance Engineering is located in Bloom-field, N.J.

The Boss and H. O. engines come with pushrod guideplates and these must be added when converting hydrau-lic cam heads to mechanical cams. In addition to thefactory units, Hank offers %" pushrods and matched

Continued on page 64

51

351 = Sleeper Continued from page 51

hardness guide plates. The Boss valve springs weigh in at315 Ib. @ 1.32" open. For maximum reliability in any en-gine we recommend the practically indestructible VascoJet springs available from many outlets.

Bolt & NutTorque Specifications

(Ft.-Lbs.)

Cylinder Head-1st step 60- 70-2nd step 75- 85-3rd step 95-105-4th step 120-5th step 125 (hot torque)

Main Bearing Cap Va-13 95-105%-16 35- 45

Main Bearing Saddle Width & Cap Fit InterferenceCon Rod Nut (with oil under nut) 45- 50Oil Pan Bolt 1/4 709

5/16 11- 13

Cam Thrust Plate to Block Bolt 9- 12Cam Sprocket to Camshaft Bolt 40- 45Flywheel to Crankshaft Bolt 75- 85Crankshaft Damper to Crankshaft Bolt 130-150Spark Plug (14 mm) 10- 15Oil Filter Mtg. to Block Insert 60-100Carburetor Mtd. Stud 4- 7Carburetor Mtd. Nut 12- 15Clutch to Flywheel 12- 20Intake Manifold Attch. Bolt %-16 28- 32

5/i6-18 23- 25Front Cover Bolt 12-15Water Pump to Front Cover Bolt 12- 15Rocker Arm Mtg. Stud 70- 75Distributor Hold Down Bolt 12- 15Exhaust Manifold to Cyl. Head Bolt 15- 20Valve Rocker Arm Cover Mtg. Bolt 3- 5

The following general installation torque specifications apply tooperations not listed below.

Thread Size Torque Ft.-Lbs.

'A-20 6- 10V4-28 6- 9'/4-Pipe 12-17

5/i6-18 14- 205/i6-24 16- 20.5%-16 25- 35%-24 30- 40%-Pipe 23- 28

7/i6-14 45- 557/i6-20 50- 60'/2-13 70- 80V2-20 85- 95Va-14 Pipe 25- 30

9/i6-18 110-130Ve-18 170-190

One little goodie that is too good to overlook is num-bered D2ZX-6670-A. This is the oil pump spring used toachieve 100 psi by-pass pressure. Also, rocker kit DOZX-6A585-A includes needle bearing rockers with bearingassembly, bearing housing, nut, shaft, and set screw.

When using quench heads TRW #L-2348-F piston givesyou12.0:1 compression without decking. When this pistonis used it is recommended that a small hole be drilled inthe piston in the oil groove above the pin hole. Then drilla hole through the pin hole from the inside of the piston tointersect the first hole. This improves pin lubrication.

For short-track applications the following recommenda-tions apply: Bud Moore 302 Mini Plenum manifold (spa-cers are required) with Holley 750 or 850 double pumper,or an appropriate Weiand or Edelbrock manifold with apair of Holley #4224 660 cfm carbs. On long tracks try theFord single-plane manifold D1ZX-9425-FA. Short tracksheaders should use 2-1/a or 2-1/2 primaries at 38 to 40inches with a 3-1/2 to 4" collector. For longer tracks theprimaries may be shortened to 30-34".

That wraps up the basic information we set out to pro-vide on the 351 Cleveland. We hope this inspires moreracers to try this engine which has strong potential.

TOP—At left is the ordinary 351 flat top piston.The pop-up piston at right gives a compression

ratio of 10.6:1 with the quench head. Neither is theticket for serious racing. RIGHT— In full street

trim the 351 Cleveland belies its potential.

64 STOCK CAR RACING