Editing Ford 335 engine (section)

=={{anchor|Cleveland}} 351 Cleveland==
===History===
The genesis of the "351 Cleveland" resulted from Ford's inability to produce enough of its new [[Ford small block engine]]-based [[Ford small block engine#351W|351 cu in]] V8s at its Windsor Engine Plant #1 in Windsor, Ontario, Canada.  Sales and marketing forecasts for the 1969 model year called for a second line, which was organized at Ford's Cleveland, Ohio, engine works.

At this time, it was also decided to upgrade the design of the new Cleveland manufactured 351s to improve performance.<ref name="Cleveland"/> Two cylinder-head designs were developed, one similar to the 351W, but with larger ports and valves, and the other with very large ports with canted intake and exhaust valves similar to the big-block [[Ford 385 engine|Ford 385 series V8]]. Sales, marketing, and product planning favored the canted valve design, as it was viewed as more innovative.<ref name="Cleveland"/><ref name="CC 351C"/>

Other changes to the engine were related to ease of manufacture and improved reliability. This led to elimination of coolant flowing through a 'dry' intake manifold, a potential source of leaks and minimized unnecessary heat transfer. To perform this change, the front of the engine block was extended to include provisions for the coolant to flow through a crossover in the block. This extension also acted as an integrated timing chain housing. The timing chain housing was covered with flat steel that was easier to seal than the typical large timing chain cover used on other Ford V8s.<ref name="Cleveland"/> These changes resulted in a bigger and heavier engine block than the small block V8s.<ref name="CC 351C"/> To help reduce costs the oil system was revised, as explained above. Although the 351W began as the basis for the 351C, by the time it reached production the design changes resulted in almost no parts interchanging between the two designs. The two engines, however, shared the same bore spacing, engine mounts and bell housing pattern.

The '''351 Cleveland''' began production in July 1969 for the 1970 model year.<ref name="CC 351C"/> Its actual displacement was {{convert|5766|cc|CID|1|order=flip}}. A conventional two-barrel "2V" (two venturi) version and a four-barrel "4V" (four venturi) performance version were built. The 351C-2V was never marketed as a high-performance engine. It used the small port 2V cylinder heads with open combustion chambers to produce a more economical passenger car engine that was tuned more for low-rpm torque.<ref name="V8Workshop"/> The 351C-4V was marketed as a high-performance engine, featuring the 4V large ports heads with closed "quench" combustion chambers. Later versions of the 351C with 4V heads continued to use the large ports and valves, but switched to open chamber heads in an effort to reduce engine emissions.  Only the Q-code 351 "Cobra Jet" (1971–1974), R-code "Boss" 351 (1971), and R-code 351 "HO" (1972) versions have four-bolt main bearing caps,<ref name="V8Workshop"/> however, all 335 series engines could be modified to have 4-bolt main bearing caps.<ref name="CC 351C"/>

===H-code===
[[File:1973 Ford Mustang convertible 351-2V Cleveland.JPG|right|thumb|250px|1973 H-code 2V 351 Cleveland]]

The H-code 351 Cleveland engines were low performance engines with low compression and two-barrel carburetors. All H-code engines ran on regular grade fuel. Compression ratio was 9.5:1 in 1970 and progressively dropped annually until it reached it low point of 8.0:1 compression in 1973 and 1974.<ref name="CC 351C pt2">{{cite web |title=The Ford 335 Series V8 Engines (351C, 400, 351M) – It Could've Been a Contender, Part 2 |url=https://www.curbsideclassic.com/blog/engines/the-ford-335-series-engines-it-couldve-been-a-contender-part-2/ |website=Curbside Classic |publisher=Curbside Classic |access-date=23 February 2020}}</ref> H-code 351s were equipped with a cast-iron crankshaft, two-bolt main bearing caps, forged-steel connecting rods, cast-aluminum pistons, non-adjustable valve train, and cast-iron intake and exhaust manifolds.<ref name="V-8 Data Book">{{cite book|last1=Sessler|first1=Peter|title=The Ultimate V-8 Engine Data Book|date=2010|publisher=Motorbooks International|location=Minneapolis, MN|edition=2nd}}</ref> All H-code 351 Cleveland engines used the small port 2V heads with open combustion chambers.<ref name="Cleveland"/> These engines were produced from 1970 through 1974 and were used on a variety of Ford models, from pony-car to full-sized.<ref name="V-8 Data Book"/> The 351W with a 2V carburetor was also produced during this time which also used the "H-code" designation. Both the 351W and 351C H-code had the same or very similar power ratings, and were used interchangeably when a car was built with the H-code engine option.<ref name="CC 351C pt2"/><ref name="Petersens Big Book">{{cite book|title=Petersen's Big Book of Auto Repair|date=1976|publisher=Petersen Publishing|location=Los Angeles, CA}}</ref>

===M-code===
The M-code was a high-compression, high-performance variation of the 351C, produced in 1970 and 1971. The M-code engines used the large-port 4V heads with a closed "quench" combustion chamber and large valves.<ref name="V-8 Data Book"/> These engines also included cast-aluminum flat-top pistons, stiffer valve springs, a high-performance hydraulic camshaft, and a squarebore [[Autolite 4300 carburetor#4300A.2C 600 CFM .281968-1974.29.5B1.5D|Autolite 4300-A]] carburetor.<ref name="Cleveland"/> The 1970 engines had an advertised 11.0:1 compression ratio and were rated at {{cvt|300|bhp|kW PS|0}} at 5400&nbsp;rpm. The 1971 version had a slightly lower advertised compression ratio of 10.7:1 due in part to the slightly larger combustion chambers, and the power rating dropped to {{cvt|285|bhp|kW PS|0}} at 5400&nbsp;rpm.<ref name="V-8 Data Book"/><ref name="CC 351C pt2"/> The M-code 351C required premium fuel and was available in the 1970-71 [[Ford Torino]], [[Mercury Montego]], [[Ford Mustang]], and [[Mercury Cougar]].<ref name="Petersens Big Book"/><ref name="71 Mustang Brochure">{{cite book|title=1971 Ford Mustang|date=1970|publisher=Ford Motor Company|edition=Sales Brochure}}</ref>

==={{vanchor |1971 R-code}} (Boss 351)===
The Boss 351 was the most potent high-performance variant of the 351C available only in the 1971 Boss 351 Mustang. Rated at 330&nbsp;bhp (246&nbsp;kW), it was fitted with a four-barrel [[Autolite 4300 carburetor#4300D.2C 715 CFM spreadbore .281971-1974.29.5B1.5D|Autolite model 4300-D]] spreadbore carburetor, an aluminum intake manifold, solid lifters, dual-point distributor, a six-quart oil pan, and cast-aluminum valve covers.<ref name="Cleveland"/><ref name="Hemmings Mustang"/> [[Forging|Forged]] domed [[piston]]s gave an 11.1:1 advertised [[compression ratio]] which made premium fuel necessary.<ref name="71 Mustang Brochure"/><ref name="Boss Registry 351C"/> It had four-bolt main bearing caps selected for hardness and a premium cast-iron [[crankshaft]] selected for hardness (90% [[nodular iron|nodularity]]).<ref name="Cleveland"/> The [[cylinder head]] was modified for better airflow, used screw-in studs with adjustable rocker arms, and except for the water passages and larger combustion chambers, were very similar to the heads used on the Boss 302.<ref name="V-8 Data Book"/> The valve train used hardened and ground push rods with guide plates and single groove, hardened valve split locks.<ref name="Cleveland"/> The forged [[connecting rod]]s were shot-peened and [[magnaflux]]ed for strength, and used improved durability 3/8-inch nuts and bolts.<ref name="Cleveland"/> The R-code Boss 351 was only installed in the 1971 Boss 351 Mustang, and it came equipped with Ram Air induction. Ford manufactured 1,806 Boss 351 Mustangs in 1971, 591 of which are registered and accounted for on the Boss 351 Registry site.<ref name="Boss Registry">{{cite web|title=Welcome to the Boss 351 Registry|url=http://www.boss351registry.com/|website=Boss 351 Registry}}</ref>

The January 2010 issue of [[Hot Rod (magazine)|''Hot Rod'']] reported a project in which a Boss 351 was assembled to the exact internal specifications of an original motor, but fitted with open, long tube, 1-3/4-inch Hooker headers (vs. the stock cast-iron manifolds), a facility water pump, a 750 Holley Street HP-series carburetor (vs. the stock 715 CFM Autolite unit), and minus the factory air filter assembly, engine accessories, or factory exhaust system. In that externally modified state it produced {{cvt|383|hp|kW|0}} [[Horsepower#SAE gross power|SAE gross]] at 6,100&nbsp;rpm, and {{cvt|391|lbft|Nm}} torque (gross) at 4,000&nbsp;rpm.<ref>{{cite journal|url=http://www.hotrod.com/techarticles/engine/hrdp_1001_muscle_car_engine_shootout/ford_boss_351_chevy_lt1_350.html|title=Muscle Car Engine Shootout - Ford Boss 351 Vs. Chevy LT-1 350|journal=Hot Rod Magazine}}</ref> A measurement of [[Horsepower#SAE net power|SAE net]] horsepower would be significantly lower, and represents a more realistic as-installed configuration with all engine accessories, air cleaner assembly, and automobile exhaust system.

==={{vanchor |1972 R-code}} (351 HO)===
The 351C HO "R-code" had a number of changes to help meet emission standards for 1972 compared to the 1971 Boss 351 "R-Code". The camshaft had less duration, but more valve lift, while the mechanical lifters remained unchanged.<ref name="Cleveland"/> The forged pistons were changed to flat-top style and the heads to open chamber heads, but retained the same large ports, valves, and adjustable valve train used in 1971.<ref name="V-8 Data Book"/> This resulted in a compression ratio decreased to 9.2:1 while the cleaner-burning open-chamber heads helped meet the new emissions regulations.<ref name="Cleveland"/> The Ram Air option was no longer available. The engine otherwise remained unchanged from 1971. This engine produced 275&nbsp;hp (205&nbsp;kW) using the more realistic SAE net system and was only available in the 1972 Ford Mustang.<ref name="V-8 Data Book"/> It was, however, now available in any body style or model of the Mustang, unlike the Boss 351.{{citation needed|date=November 2022}} The 3.91 [[Traction Lok]] rear and four speed were still the only available drivetrain.{{citation needed|date=November 2022}}

==={{vanchor |Q-code}} (351 Cobra-Jet)===
The Q-code 351 "Cobra-Jet" (also called 351-CJ, 351-4V) was produced from May 1971 through the 1974 model year. It was a lower-compression design that used open-chamber 4V heads.<ref name="V-8 Data Book"/> The open-chamber heads exhibited superior emissions characteristics and were used to meet the more stringent emissions standards for 1972 and beyond.<ref name="Cleveland"/> The "351 CJ" high-performance engine included a different intake manifold, high-lift, long-duration camshaft with hydraulic valve lifters, higher rate valve springs with dampers, a 715-CFM spread-bore 4300-D Motorcraft carburetor and a dual-point distributor (only with four-speed manual transmissions - not sold in California). The block was upgraded to four-bolt main bearing caps, and larger harmonic balancer was installed. These engines also featured induction-hardened exhaust seats for use with low-lead and unleaded gasoline.<ref name="V-8 Data Book"/> This engine was different from the 1970-71 M-code 351C having a more aggressive camshaft, a spread-bore carburetor, a four-bolt block<ref name="Boss Registry 351C">{{cite web|title=351 Cleveland|url=http://www.boss351registry.com/351_Cleveland.htm|website=Boss 351 Registry|access-date=3 June 2014}}</ref> and the lower compression allowed regular fuel to be used.<ref name="1972 Torino Brochure">{{cite book|title=1972 Ford Torino|date=1971|publisher=Ford Motor Company|edition=Sales Brochure}}</ref> It was rated at {{cvt|280|bhp|kW PS|0}} for all 1971 applications. For the 1972 model year, the only change to the engine was a retarding the camshaft events by 4°.<ref name="Cleveland"/> The engine was rated at {{cvt|266|hp|kW|0}} (SAE net) for 1972 when installed in the Mustang, and {{cvt|248|hp|kW|0}} in the Torino and Montego.<ref name="V-8 Data Book"/> An increase in the combustion chamber size and the use of smaller valves occurred in 1973,<ref name="Cleveland"/> which reduced horsepower to {{cvt|246|hp|kW|0}} for the four-barrel for the intermediate Fords, though it still retained the higher {{cvt|266|hp|kW|0}} rating in the Mustang.<ref name="V-8 Data Book"/> The 351 CJ (now referred to as the "351 4V") was rated at {{cvt|255|hp|kW|0}} in 1974 and was only installed in the [[Ford Ranchero]], Ford Torino, Mercury Montego, and Mercury Cougar.<ref name="Hemmings Mustang">{{cite web |last1=Traver |first1=David |title=Last of the Hot Rods - 1973 Ford Mustang |url=http://www.hemmings.com/mus/stories/2010/02/01/hmn_feature7.html |website=Hemmings |date=February 2010 |access-date=3 June 2014}}</ref>

===Replacement===
Production of the 351C ceased at the end of the 1974 model year. The engine was replaced by the [[#351M|351M]] for the 1975 model year. This new variation used the same bore and stroke dimensions of the 351C, but used the tall deck block from the 400 V8 engine and was only available with a 2 barrel carburetor.

===351C engine specifications chart===
{| class=wikitable align=center
|+''351 Cleveland engines''<ref name="Cleveland">{{cite book|last=Hammill|first=Des|title=Ford Cleveland|date=Sep 2011|publisher=Veloce Publishing|location=Dorset England}}</ref>
|-
!Code!!Engine type!!Years!!Compression!!Combustion Chamber!!Camshaft Duration!!Camshaft Lift||Tappets!!Main Bearing Caps||Notes
|-
!H
|351C-2V||1970–1974||Low||Open Chamber||258° I/266° E 32° overlap||0.400" I/0.406" E||Hydraulic||2-bolt||
|-
!M
|351C-4V||1970–1971||High||Closed Chamber||266° I/ 270° E 34° overlap||0.427" I/0.427" E||Hydraulic||2-bolt||
|-
!R
|351C-4V "[[Ford Boss 351 engine|Boss 351]]"||1971||High||Closed Chamber||290° I/ 290° E 58° overlap||0.467" I/0.477 E||Mechanical||4-bolt||Rare
|-
!R
|351C-4V HO||1972||Low||Open Chamber||275° I/ 275° E 35° overlap||0.491" I/0.491" E||Mechanical||4-bolt||Very rare<ref name="Hemmings Mustang"/><ref group="note">Only 398 Ford Mustangs with the 351C HO engine were produced, according to production data from Ford.</ref>
|-
!Q
|351C-4V CJ|| May 1971 – 1974||Low||Open chamber||270° I/ 290° E 48° overlap||0.480" I/0.488" E||Hydraulic||4-bolt||cam timing retard 4° in 1972, compression reduced in 1973
|}