In part one of this series, the history and design fundamentals of Ford’s 335-series engines were examined. This article will delve into the details of numerous engine iterations of the Ford 335-series. Only being offered from 1970-82 in the North American market, Ford created a wide variety 335-series engines despite its short life span. The 351C had the most variations, which ranged from family car engines to one of the hottest engines of the muscle car era.
Ford enthusiasts typically identify engines by their VIN code, rather than the option code like on GM cars. So, as we examine each of the 335-series engine iterations, they will be identified by their configuration and engine code.
The 351C-2V: H-code
The 335-series engines were designed with high performance aspirations and racing potential in mind, but the fact was that the vast majority of the engines being built would be very conventional and installed in regular cars that had little to no performance ideations. This is where the 351C-2V comes into the picture. This engine was the low performance everyday 351C and was the most commonly produced version. The 351-2V used the open chamber heads with the small “2V” sized ports and a mild short duration, low lift camshaft. It was rated at 250 hp and 355-ft lbs (gross) for 1970, had 9.5:1 to compression and could run on regular fuel.
Due to the ever tightening emissions standards, Ford made annual changes to help ensure the engine would burn cleaner. For 1971, 1972 and 1973 year the compression fell to 9.0:1, 8.6:1 and 8.0:1 where it stayed until the engine went out of production in 1974. This was done with an increase to the combustion chamber size in 1971 and in subsequent years by increasing the piston dish volume. To further aid cleaner emissions, Ford retarded the camshaft timing by 4 degrees and added an EGR system in the 1973 model year. The retarded camshaft timing significantly hurt performance and engine response, as this change effectively lowers the dynamic compression ratio. These changes caused reductions to the horsepower ratings; in its final year it was rated at 162 hp (SAE net).
It should be noted that Ford used the “H-code” interchangeably between the 351W-2V and the 351C-2V. Ordering a 351-2V engine meant that you could get either version but both the 351C-2V and 351W-2V H-Code engines had basically identical power outputs. The H-code 351C-2V was mostly used intermediate and pony car Ford and Mercurys but some full-size cars got them too.
The 351-4V: M Code
When Ford began to advertise the “new” 351-4V for 1970, this was the engine it was writing about. While the H-code 351-2V was pretty vanilla, this engine was designed to appeal to the performance enthusiast. The M-Code 351C had an Autolite 4300-A 630 CFM carburetor, large port 4V cylinder heads with small “quench” combustion chambers, 2.19”/1.71” valves and flat top pistons. The advertised compression ratio was 11.0:1, although this was somewhat inflated (the measured compression ratio was actually 9.95:1). Nevertheless, premium fuel was mandatory. Because of the excellent breathing abilities and the high compression ratio, this engine used a relatively mild camshaft with 268/280 degrees of duration and 0.427/0.453” of lift, and still was able to produce 300 hp and 380 ft-lbs of torque (gross).
This engine was only available in the FoMoCo’s more sporty cars, which meant the Torinos, Montegos, Mustang and Cougar. For 1971, to reduce emissions, Ford dropped the compression ratio by increasing the combustion chamber size. This resulted in the advertised compression ratio dropping to 10.7:1 (measured compression ratio 9.59:1). There were no further revisions to the engine, and the horsepower rating dropped to 285hp and 370 ft-lbs (gross). The M-code went out of production after 1971.
The M-Code 351-4V was decent performer. In Motor Trend’s Car of the Year test, a 1970 Torino quipped with a 351-4V consistently out accelerated a more powerful 360-hp 429 Torino. Motor Trend said “Run-for-run the lighter 351 Torino is the quicker accelerating [car].” Car Life commented in its road test of a 1970 M-Code Torino that “this is the first really good mid-sized engine from Ford.”
351-4V Cobra-Jet: Q-Code
The closed chamber high compression heads used on the M-code 351-4V were not conducive to clean emissions. In the spring of the 1971 model year, Ford added the low compression cleaner burning 351 Cobra-Jet to the Ford Mustang line. For the 1972 model year the 351-CJ fully replaced the discontinued M-code 351C while all high performance variations of the 429 (for civilian cars) were discontinued. This meant the 351C-4V was Ford’s only high performance engine. Reducing the compression ratio of an engine dramatically lowers its performance. Nevertheless as the last performance engine, Ford engineers went all out to produce one of the best emissions friendly performance engines of the era.
To ensure the engine would burn cleaner, the 351-CJ used open chamber 4V cylinder heads. The larger open combustion chamber decreased the compression to an advertised 9.0:1 (actual compression was 8.74:1), allowing it to burn regular fuel. These heads still used the same large 4V ports and valves that were also used by M-Code engine. To help compensate for the decrease in compression, Ford used a more aggressive camshaft. The camshaft duration was increased to 270/290 degrees and lift was increased to 0.481/0.490 inches. To compliment the new cam, cars equipped with this engine got a small diameter high stall torque converter. Ford engineers made other improvements over the M-Code, including a stronger 4-bolt main block, and a larger 750 CFM Autolite 4300-D carburetor. The end result was the engine being rated at 280 hp, only 5 hp less than the 1971 M-code.
For 1972 the 351-CJ production was in full swing, and it was used in the Mustang, Cougar, Torino and Montego. The engine only saw one minor revision from the 1971 version, being the camshaft timing retarded 4 degrees. With the introduction of the SAE net ratings for 1972, Ford went a little strange on rating their engines. Unlike the other manufactures, Ford had multiple ratings for identical engines. So, the 351CJ was now rated at 266 hp in Mustangs and Cougars and 248 hp in the intermediate cars, despite the fact they were identical. For 1972, both numbers were very good, especially for a mid-sized displacement engine. Nevertheless, even federally certified Q-code engines were saddled with emission control devices that hampered drivability and part throttle performance.
Facing ever tightening emissions standards, for the 1973 model year an EGR valve was added to the 351-CJ. The combustion chamber sized was increased further and the pistons used a small dish which decreased the compression to 8.0:1 advertised (8.12:1 measured). Although the 4V heads large port heads were used, the valve sizes were reduced to 2.04”/1.65”, the same as the 2V heads. Interestingly, these 4V heads with the smaller valves actually have excellent performance potential, since the small valves are less shrouded in the 4” bore. The end result was a minimal power rating difference from 1973, with the Mustang/Cougar engine still rated at 266 hp (SAE net) and the Torino/Montego engine rated at 246 hp (SAE net).
1974 was the last year for the Q-Code engine. With the Mustang switching to the smaller Mustang II platform, the engine was now only offered Ford/Mercury intermediates. Ford was still inconsistent with its horsepower ratings and despite no changes from the 1974 engine, the Q-code rating was revised to 255 hp (SAE net).
The Q-Code 351-CJ was a good performer for its day and had output as good as or better than other de-smogged competitors, such as Chevrolet’s LT-1 and L-82 and Chrysler’s 340. This version of the 351 also powered the many DeTomaso Panteras. Road Test magazine tested a 1972 Mercury Montego MX with a 351-CJ. They said “Despite a two point drop in compression ratio…[this engine] remains a potent performer.” However, Cars Magazine noted the decreased driveability in a road test of a 1972 Ford Gran Torino Sport with a 351CJ. They said “Throttle response isn’t what it used to be and you just have to accept the sloppier performance dictated by the use of smog controls.” Most 1972 cars with a 351-CJ ran the ¼ mile in the mid to high 15 second range, while later iterations were slightly slower.
Boss 351/351 HO: R-Code
The 1970 M-Code 351C was a relatively mildly tuned engine, even though it was rated at 300 hp. Ford unveiled the true potential of the 351C with the Boss 351 engine introduced partway through the 1971 model year. This engine was one of Ford’s most impressive performance engines of the era. The Boss 351 started with a 4-bolt main block, 4V quench chamber heads, forged domed pistons, and forged connecting rods that were shot-peened and magnafluxed with 180,000 PSI 3/8-inch nuts and bolts. Compression was advertised at 11.0:1 (10.63:1 measured), meaning premium fuel was required. All 335-series engines used high-nodular cast iron crankshafts, but Boss 351 cranks were specially selected to have more than 90% nodularity. The solid lifter camshaft had 290/290 degrees of duration and 0.477”/0.477” of lift. It used more durable single groove valves and stiffer valve springs. The solid lifters required adjustable valve train. Consequently, the R-code engines used adjustable rocker arms mounted on screw-in studs rather than the bolt down pedestal mounts of the hydraulic lifter engines. The R-Code engines were the only 335-series engines that used an adjustable valve train.
With the big free flowing ports and valves, this engine needed to breath, so it was equipped with a low restriction aluminum intake manifold and an Autolite 4300-D 750 CFM carburetor which was fed by a Ram Air induction. Rather than stamped steel valve covers, the Boss got finned cast aluminum valve covers. For 1971 the R-Code was only available in the Mustang, as the Boss 351. In total, there were only 1,806 Boss 351 Mustangs manufactured for the 1971 model year.
The R-Code Boss 351 was rated at 330hp (gross), only 5 hp less than the 428 CJ. We all know engines were over and underrated at this time, but based on the performance times that the Boss 351 ran in the larger, heavier 1971 Mustang, it probably wasn’t putting out much less power than a 428 CJ. Car and Driver was able to run the quarter mile in 14.1 seconds at 100.6 mph. With powershifting, the car hit 13.9 seconds at 102 mph. Car and Driver said “The engineers come off as the real heroes in the development of the Mustang Boss 351. It offers drag strip performance that most super cars with 100 cu. in more displacement will envy and generates high lateral cornering forces.” Motor Trend was also impressed with the Boss 351’s performance and were able to better the C/D times, running the quarter mile in 13.8 seconds at 104 mph.
The Mustang Boss 351 only lived for one year, but the R-Code 351 survived for one more year. Ford had to revise the R-Code for 1972 to pass the tighter emission standards. In doing so it lost a fair bit of power and performance. Ford renamed it the 351 HO and like the 1971 engine, it was only available in the Mustang. Ford struggled to get this engine emission certified and as a result it wasn’t available until the latter half of the 1972 model year. Only 398 engines were produced.
To reduce the emissions, Ford lowered the compression to an advertised 9.2:1 (9.0:1 measured). This was accomplished by switching to open chamber combustion chambers and flattop pistons. The camshaft was revised to have less duration, 275/275 degrees, but compensated with slightly higher lift of 0.491”/0.491”. It continued to use the same carburetor and intake, but the carburetor was recalibrated for cleaner emissions. The only other change was that the Ram Air system was no longer used.
As a result, this cleaner R-Code engine performed well by 1972 standards, but the decrease in driveability and performance was noted. A 1972 Mustang R-Code was tested by Car and Driver. It ran the ¼ mile in 15.1 seconds at 95.6 mph. This was about 1 second slower and 5 mph slower than the 1971 Boss 351. Car and Driver said “This year they call it the 351 HO: last year it was the Boss. Ford hasn’t dropped the Boss part for nothing.” The Ford engineer on hand during the test talked “about potential rather than what the 351 does right out of the box. Emissions comes first these days, power second.”
After the 1972 model year, Ford dropped the R-Code 351C, leaving the Q-Code as its only performance engine.
400-2V: S- Code
The 400 was deigned similarly to the H-Code 351C, as a regular engine for everyday cars. As such, it was only produced as a regular fuel, mildly tuned, low-performance 2-barrel engine. There was never a production 400 4-barrel produced. 400s used a 2V open chamber head that was virtually identical to the 351-2V and a mild camshaft designed for low end torque.
For its 1971 model year introduction, the 400 was rated at 260 hp and 400 ft-lbs of torque (gross). The 400 only produced 20 more horsepower than the 1971 351-2V, but it produced a significant 50 lbs-ft more torque and at a lower RPM peak. Road Test magazine tested a 1971 Ford LTD Brougham with a 400-2V engine. They said the 400 is “pretty much a carbon copy of the advanced, light, tough 351, it produces 400 lbs-ft of torque at a rather low (for a V8) 2,200 RPM.” They went on to say that the “ the extra 20 horsepower the engine provides over the base 351 makes the car noticeably livelier” and that “The new 400 is smooth and responsive with an excellent low end toque curve… a really heavy footed driver starting from idle can fast wear down the right rear tire.”
Like the 351C, the 400 had to be quickly adapted to the ever tightening emissions standards, so minor changes occurred in 1972. Ford reduced the compression ratio slightly to 8.4:1 by using dished pistons. For 1973, the 400 had its compression reduced again, now at 8.0:1. Ford also now used a timing set that retarded the camshaft timing 6 degrees, effectively reducing the dynamic compression ratio further.
After the addition of electronic ignition in 1974, the 400 saw significant changes for the 1975 model year. The much more strict 1975 emissions requirements caused the cylinder heads to be redesigned. The new castings had more restrictive exhaust ports due to the redesigned cooling jackets and cast-in Thermactor passages. This along with the newly introduced restrictive catalytic converters resulted in the 1975 400 being the lowest performing variant.
Ford continued to revise the 400 on a yearly basis. Horsepower increased the output from the 1975 low point of 158 hp to a high of 180 hp until it dropped back down again to 159 hp in 1979, the last year it was offered in passenger cars. However, further changes occurred in 1977 when Ford introduced the 400 into the truck line-up. Since the engine could be equipped with a manual transmission in trucks, Ford introduced an engine block with strengthened main bearing webs, making it one of the strongest factory engine block castings of all 335-series engines. These reinforced blocks were also phased into passenger cars once the old castings were used up. By the end of the 1979 model year the 400 was phased out of the car line-ups but it remained available until the 1982 model year in Ford trucks.
The 351M-2V: H-code
By the 1975 model year, Ford had no performance engines in its line-up. Concern shifted to producing engines that were clean burning and to lower production costs. Consequentially, the 351C ended production in 1974 and was replaced with the 351M. The whole purpose of the 351M was to reduce production costs. Rather than having two engine block sizes, the short deck 351C and tall deck 400, it was cheaper to destroke the tall deck 400 to produce a 351 ci engine. This maximized part interchangeability between the two engine displacements. The new 351 was given the “M” designation to distinguish it from the 351C and the 351W. Most agree the “M” was for modified, but some claim it was “Michigan” or “Midland.” Ford never said what it meant officially. Of note, the 400 Ford has no designation, despite the commonly misused 400M moniker. Why would Ford need an identifier when it only produced one 400?
Visually, the 351M looked very similar to the 351C and many can mistake the two at a glance. The 351M, however, was wider and taller like the 400 to which it was visually identical. It shared almost all of its components with the 400, with the only unique parts being the pistons and the crankshaft. Since the 351M used the same block as the 400, it also used the same motor mounts and the same larger bell housing pattern of the 400.
The 351M was a low-performance engine and was only equipped with 8:1 compression and a 2-barrel carburetor. Like the 351C-2V that preceded it, it was equipped with 2V heads that used the smaller ports and valves. However, it used the more restrictive cylinder head castings that the 1975 and newer 400 used. The 351M was also saddled with retarded camshaft timing, and the rudimentary emissions controls of the day that compromised driveability.
Just like the 351C-2V, the H-Code 351M was used interchangeably with the H-code 351W-2V. This meant that if you ordered a 351-2V engine, you could have randomly ended up with either version of the engine. The only exception to this rule was Ford’s compact Granada and Monarch and the 1979 Panther cars, which used the 351W exclusively and Ford trucks which used the 351M exclusively. Nevertheless, both engines were saddled with equally bad tuning as a band aid to help produced cleaner emission, and both were rated within a few horsepower of one another for each model year. Throughout its production, the 351M-2V engine typically produced approximately 150 hp (net), but some versions were even less.
Both the 351M and 400 Ford engine blocks developed a reputation for cracking, but the reality was it this was only a problem for some of these engines. The 400 engine blocks were cast at the Dearborn Iron Foundry and the Cleveland Foundry for 1971-1972 and had no issues. For 1973 and beyond, the blocks were cast at the Cleveland Foundry or the Michigan Casting Center. Only engine blocks cast before March 2, 1977 at the Michigan Casting Center are prone to cracking. After that date, the Michigan Casting Center blocks were corrected.
The 351M was a compromised design. While it still possesses all of the advantages of the 335-series family, it was saddled with the worst heads and was produced during the darkest days in Detroit. Like the 400, the 351M was last installed in Ford passenger cars in 1979 and Ford trucks for the 1982 model year. While there is potential to build a 351M today to be a better performer, limited aftermarket support means there are no off-the-shelf high performance pistons options. In addition, the 351C has a lighter block, and less rotating mass for the same displacement. Today, many believe the best was to build a 351M is to replace the crankshaft with a Ford 400 crankshaft or an aftermarket stroker crankshaft.
Australian 351C and 302C
For the 1970 model year, Ford of Australia started to import 351C engine assemblies from Ford of USA to replace the formerly imported 351W. The 351Cs imported to Australia were the same two variants offered in the US market, the 351C-2V and a 351C-4V. Like the US, the majority of the engines sold were the low performance 351C-2V.
In November 1971, Ford of Australia began to manufacture the 351C locally. The Geelong engine plant imported engine blocks cast in the USA, but the remaining engine parts were manufactured at the Australian plant. Geelong built both a 351C-2V and 351C-4V, but they were not the same as the US market engines. To save on tooling costs, Ford of Australia only cast one cylinder head, which was essentially the same as an American market 351-2V cylinder head. That meant all Geelong built 351Cs used large open chambers and the smaller 2V ports. Consequentially, Geelong also had to cast a unique 4-barrel intake manifold that was compatible with the small port heads.
Geelong only had the tooling to produce the 351C engines, meaning the base 302 engines would still need to be imported from the USA. This would result in the 302 costing more than the locally produced 351C. So, Ford of Australia decided to produce its own 302 variant using the 351C as the basis. By destroking the 351C with a 3” stroke crankshaft, Geelong created the Australian market exclusive 302C. Similar to the 351M, the 302C’s design was compromised in order to minimize production costs.
The 302C and 351C shared the same engine block and pistons. However, to do so, the 302 required longer 6.020” connecting rods. This resulted in a less than ideal connecting rod-to-stroke ratio of 2.01:1. The 302C used a unique cylinder head design. The shorter stroke required a smaller combustion chamber to produce an acceptable compression ratio. To do so, the quench combustion chamber was utilized, which decreased the combustion chamber to a volume of 56.4–59.4 cc. This was the smallest combustion chamber of any 335-series engine cylinder head. Since this was a small displacement low-performance engine, the 302C head used the small 2V ports and valves. So, the 302C cylinder heads were the only cylinder heads with a quench combustion chambers and the small 2V ports.
Ford of Australia received news that Ford of USA was stopping production of the 351C in the US market after the 1974 model year. Geelong purchased the US tooling so that it could begin to cast its own cylinder blocks. To ensure there was no engine production stoppage, Ford of Australia ordered 60,000 engine blocks from Ford in the USA. By 1975 Geelong began casting engine blocks. Production of the 302C and the 351C continued until December 1981, but supplies lasted until the mid-1980s. These Australian Cleveland engines were not only used in Ford cars, but also were used in Australian market Ford F-Series trucks, making them the only Ford trucks to get 351Cs. The Australian built 351Cs were also used by DeTomaso after the supply of US made 351Cs was exhausted.
NASCAR continued to use the 351C well past 1974 and by 1975 the American made block supply was almost depleted. As a result, the Geelong Foundry began to cast new engine blocks for NASCAR. Like the American made NASCAR blocks, the Geelong NASCAR blocks were strengthened for racing. These Geelong made NASCAR blocks were used until the mid-1980s when it was replaced by a new American made Windsor based racing block. I wonder how many NASCAR fans had any idea that the Fords of that era were using “imported” engine blocks!
The Ford 335-series engine was a short lived engine family. While it never got to live to its full potential, today, these engines still are used and loved by a small and dedicated group of enthusiasts. I hope after reading these articles, the excellent design and engineering of this engine family can also be appreciated by fellow CCer’s.