Ford offered two versions of the 351 engine, a Windsor 351 and a Cleveland 351. The Windsor motor is considered a small block. The Cleveland 351 is between a small block and a big block. Even though the Cleveland 351 came from the small block family, few parts will interchange. The heads on the 351 4 barrel engine were very similar to the Boss 302 heads.In 1971, Ford offered only a two barrel version of the 302 motor. The Boss motor option was called the Boss 351. The 1971 Boss 351 could be called Ford's greatest performance small block motor.
In mid May of 1971 Ford introduced a new version of the 351 Cleveland motor. It was during these years that the performance engines were under a lot of pressure. Insurance rates were going up on cars with these motors. High octane gasoline was getting harder to find. New air quality standards put better smog controls on the motors, affecting the performance. The mid '71 Boss 351 (Cobra Jet) engine wasn't much of step up from the stock 4 barrel motor. It featured:
First offered in 1970, the 351 Cleveland motor came as a 2V and a 4V engine. The heads and carbs were the difference. The 4 barrel 351 Cleveland had:
| 4 Barrel 351 Cleveland | 2 Barrel 351 Cleveland | |
| Bigger valves | ||
| Larger intake and exhaust valves | ||
| Smaller quench combustion chambers | Large, round "open" chambers | |
| Cast iron dual plane intake | ||
| Hotter hydraulic cam | ||
| Autolite carb | Autolite carb | |
| 10.7:1 compression | 9.0:1 Compression | |
| Rated at 285 horses | Rated at 240 horses | |
Four bolt mains
Hydraulic cam slightly hotter than the stock 4 barrel motor with a little longer duration
Different heads - large ports & valves of the 4 barrel with the open design of the 2 barrel version
Cast aluminum flat top pistons
9.0:1 compression (Compared to the 10.7:1 in the 4 barrel motor)
Spread bore Autolite carb with smaller primaries and larger secondaries
Same Cast iron intake as the 4 barrel Cleveland
By 1972 the Boss motors were gone. The Boss 351 of '72 was in name only. The motor was the same as the stock 4 barrel 351 Cleveland. The compression was 9.0:1 in both motors. The cam timing was retarded 4 degrees. In 1972 the Cobra Jet motor was renamed HO for high output. All the heavy duty parts were kept but the compression went to 9.2:1. The heads were open chamber instead of the semi-hemispherical. The pistons were flat top and forged. The solid lifter cam had a little less duration (275 degrees) and more lift (0.491"). the following year, 1973, was the 4 barrel Cleveland 351's last year. The two barrel version was rated at 160 horsepower. The pistons were dish topped. The four barrel was rated at 266 horsepower. Compression dropped to 8.0:1.
Gone was a great motor. Even today the 351 is an engine of choice. It will bolt in place of a 289 or 302. For practically any application, the Ford 351 Cleveland is the performance choice with plenty of horse power and torque.
In 1972 the 351CJ was retained. VIN engine code "Q". Same basic engine as the 1971 "Q" code. Lower compression heads and hydraulic cam. The H.0. engine was a seperate engine with VIN engine code "R". This engine is almost identical to a 71 R code Boss 351, and was even refered to as the Boss 351 in Ford literature. but the lawyers made them change the name. It actually had a larger lift cam the 71 version, although the duration was less. It had solid lifters, and most of the other associated parts. Compression was around 9.2 with open chamber heads and a Forged flat top piston with a single valve relief. For more info go to.... http://www.boss351.org/HO.htm
The Boss 351 was a very unique motor. It had all of the best Ford could offer:
Heads just like the Boss 302 with canted-valves Canted-valves (2.19" intake and 1.71" exhaust)
Compression chamber of 66-67 cc (compared to the Boss 302's of 57-60 cc)
Four bolt mains - specially hardened
Cast Crank shaft with 90% nodularity
Forged steel rods - shot-peened & magnafluxed with heavy duty 3/8" bolts and nuts
Forged aluminum pistons with pop-ups
11.1:1 compression
Mechanical camshaft of 290 degrees of duration & 0.477" of life
Hardened and ground pushrods and guide plates
Aluminum dual plane intake manifold
Autolite 4300-D carb
1970-1973
Cleveland
1969
Windsor
1971-1972
Boss 351-HO
1969-73
90 degree,
Overhead Valves (OHV)
90 degree,
Overhead Valves (OHV)
90 degree,
Overhead Valves (OHV)
90 degree,
Overhead Valves (OHV)
380 lbs./ft. @ 3,400 RPM
(1971)
275 lbs./ft. @ 6,000 RPM
(1972)
330 BHP @ 5,400 RPM
(1971)
275 BHP @ 6,000 RPM
(1972)
(1969-70)
177 BHP @ 4,600 RPM
(1971-73)
(Number 1 cylinder on right bank, nearest radiator)
(Number 1 cylinder on right bank, nearest radiator)
(Number 1 cylinder on right bank, nearest radiator)
(Number 1 cylinder on right bank, nearest radiator)
(101.6 mm X 88.9 mm)
(101.6 mm X 88.9 mm)
(101.6 mm X 88.9 mm)
(101.6 mm X 88.9 mm)
9.2:1 (1972)
Autolite 4300-A (4V)
Squarebore
automatic choke
Squarebore
automatic choke
Squarebore
automatic choke
premium gas (1972)
cast iron (1972)
EXP 132/505