Those of us blessed with 77-79 and later Ford Trucks might not feel so blessed when the urge strikes for a performance upgrade. While the aftermarket is filled with go-fast goodies for the 302/351Windsor, and the mighty 460, the 351M / 400 mill was never really thought of as "performance engine." Odd really, considering it's very "performance oriented" heritage.

Background

The 351M / 400 engines came at a time when Ford's Windsor plant couldn't keep up with the demand for mid-size engines coming from the truck and big car divisions. The FE series had reached the end of it's production run, leaving the boys at the blue oval in a bit of a dilemma. They wanted an engine of moderate size with the torque of a big block, and enough fuel/emissions efficiency to meet the growing governmental demands on the industry. They failed miserably. Blasphemy? No, cold, hard reality. In their stock form, and mated to full time 4WD transfer cases, the M/400 engines were grossly under powered, returned hideous fuel mileage, and weren't exactly the air scrubbers on wheels the Feds were looking for. There are many reasons for the M/400's less than inspiring performance. . . Strange when you stop and consider that the engines are nothing more than a tall-deck "Cleveland". You remember the 351 Cleveland don't you? It dominated NHRA Pro Stock Drag Racing before the dawn-of-the-mountain-motor was effectively banned from NASCAR for the sin of breathing "too well." It unleashed terror on the streets in it's "Boss 351" Mustang trim. So what happened? The short version is that the engineers at FoMoCo tried to make a fire breather into something it wasn't and only succeeded in producing a dud. Rather than rehash the history as to "why" they did it, you're probably a lot more interested in "how" to correct their mistake.

It's all in your heads

Or more precisely, your engine's heads. Sitting atop the M/400s are the 2V versions of the 351 Cleveland heads - the very same pieces bolted to 10's of thousands of 351 Clevelands throughout the early 70s. The 2V heads feature 2.07 in. intake valves, open chambers, and ports sized to shame their famous "2.02 Camel Back" Chevy counterparts. In an airflow comparison with Ford's own SVO GT-40X High-Po aftermarket heads, the numbers speak for themselves.

For a street / performance 4x4 application, the 2V heads are preferred over the 4V versions because of their superior low end torque. The tennis ball size intakes of the 4Vs may be the ticket to high-RPM bliss, but they are more a hindrance than help in most 4x4 applications. The open chamber design presents the first of the engine's serious performance shortcomings. Designed for low compression / emissions purposes, the open chamber configuration results in significant torque/HP loss over the closed chamber design of the Boss / HO 4V head. I know what you're thinking - wouldn't it be great if Ford had made the heads with the high efficiency 2V ports and the high compression of the closed combustion chamber? They did. Unfortunately, they were only available in Australia. If you're lucky, you can find them at auto swap meets, but you'll have better luck importing a set from an Aussie scrap yard. Hey, we never said this would be easy. For most of us, the Aussie route is prohibitive in one way or another, so the only real way to achieve the needed boost in compression is through flat top or domed pistons. While a look through performance catalogs won't yield much in the way of high compression replacements, there's a little known, and fairly easy solution to custom slugs. Use 351 Cleveland pistons with bushed connecting rods. Since the 351C and 351M/400 pistons utilize wrist pins of different diameters, a machine shop can re-size the M/400 rods to accommodate the proper pin. You'll then have access to pistons ranging from the stock 8 to 1 compression ratio, up to race gas only territory. A realistic ratio falls between 9 and 10 to 1. Any higher and you'll need octane booster. With a two-point jump in compression, an increase of 50 HP is a very conservative estimate, based on no other changes. Once you establish a solid compression ratio, those big valves and ports will really start to pay dividends. But don't stop there.

Oh, "Cam" on...

The biggest problem the M/400 has, hands down, is the fact that FoMoCo chose to retard the cam by four degrees to meet emissions requirements. Face it. Big valves and ports are useless when there's little air/fuel flowing through them into the combustion chambers. That said, the obvious solution is to ditch the stock cam, lifters, and timing chain in favor of more performance oriented versions. With 10-to-1 compression, you can effectively use a pretty wild cam, but more isn't better when camming an off-roader. Unless you're planning on running a high stall converter in a mud truck or prerunner, you'll be better served with a saner profile. Look for a cam in the .520-.550 gross lift / 260-272 degree duration range. Keep in mind that the Clevelands are more "intake efficient", so a dual pattern cam favoring the exhaust side is often a good choice. The advent of roller cam conversions opens up another possibility for the M/400 enthusiast. The greater efficiency of the design results in significant performance / mileage gains over a comparable hydraulic profile. The added cost for the roller is insignificant when weighed against it's benefits. Don't even think about a stock replacement timing chain. Go with a roller chain assembly and run the cam "straight up" For example, zero degrees advanced/retarded to regain the horsepower the factory threw away. Give serious consideration to adding matching valve springs, retainers, and push rods. Some cam builders require these pieces to maintain warranty. If you're going to a bigger cam, it's a good idea to get the springs to match. Otherwise, your new "thunderstick" may well fatigue the stock pieces quickly, resulting in catastrophic engine failure. Lastly, roller-rocker arms are a smart replacement for the stock units. Less friction means more power and efficiency, and you don't need a 10,000 RPM screamer to realize those kind of benefits. Another important point to consider is that the production tolerances of the factory stamped steel rocker arms vary widely. With a theoretical ratio of 1.73 to 1, you could be losing considerable lift and duration at the valve, which adds up to significant loss of horsepower.

Slippery Situations

Clevelands have a reputation for oiling problems, but they usually manifest at high RPM. High volume oil pumps are cheap insurance against an early death at any RPM. If you're anticipating a lot of highly angular travel, baffling the oil pan with kits from Moroso, Milodon, or others will help keep the oil pump pick-up from cavitating., and the oil flowing to the bearings where it belongs. Moroso also sells an "Accumulator", which will force an additional quart into the system in the event of a sudden pressure drop. Speaking of oil, go Synthetic. Greater lubricating properties and reduced friction equal "free horsepower". Every little bit helps.

Big Gulps

Clevelands will consume a sick amount of fuel if you let them. It's like handing a kid a tub of ice cream and a spoon, then leaving him to his own devices. The trick here is giving them just enough to keep them happy. According to Holley's charts, a 400 cid engine requires less than 600 cfm of flow at 5000 RPM. Sure, you can bolt on a 750 cfm or even larger carb, but you'll kill low end driveability and fuel efficiency if you give in to the temptation. Rather than striving for a 4WD dragster, stick with a smaller carb, and spend the time jetting it right. Clevelands respond well to large accelerator pump shots, and crisp jetting. While no single plane intakes are currently in production for the M/400, Holley markets adapters to mate the 351 Cleveland intakes to the taller deck block. Clevelands like single plane manifolds - A lot. You'll need to increase the pump shot considerably, but the results in mid to upper rpm horsepower are more than worth it. For those choosing the dual plane route, Edelbrock, and Weiand offer aluminum intakes that are worlds above the stock (and heavy) 2BBL intakes. The benefits of a dual plane are primarily low to mid rance HP - just the opposite of the single plane. Determine your driving style, and choose according to your needs.

Old Sparky

Igniting the fuel is of prime importance to any engine. While the Duraspark ignition is OK for a stocker, it's far behind today's aftermarket buzz boxes. You can pick your poison among the top quality brands and be rewarded with added performance and efficiency. Just keep it simple! There's a big difference in price between a performance and "race only" ignition, but at streetish RPM levels, there's no benefit to running the ultra high-end pieces. In fact, there may be a performance loss. Some of these volt monsters are designed for short use (1/4 mile style), and will fail under sustained street use. If you want to spend wisely, go conservative on the buzz box, and apply the difference to an aftermarket distributor. Aside from accurate timing (which boosts performance on it's own), you'll get the benefit of adjustable advance - mechanical, vacuum, or both. Clevelands like advance - early, and in quantity. That's something you won't get with a stock distributor. Adjustable distributors will take some time to tweak to your particular engine, but again, the results are well worth the effort.

Exhaust Upgrade

Stock manifolds are passable at best, and a set of headers will unlock hidden horses from an otherwise free breathing engine. 1-3/4 in. to 1-7/8in. primary tubes are about all a 400 cube engine with a 5000 RPM ceiling will ever be able to use. Don't get crazy in tube diameter - you'll kill the low end outright. A 2 1/4 to 3 inch dual exhaust system with free flowing mufflers will result in a good match for this engine. If you're more of a crawler type, go small to boost the low end. If speed is what you need, go to the 3 in. pipe, Just remember to be realistic in your driving habits when selecting tubing diameter from the primaries on back. You'll be happier in the long run. Also consider a crossover "H" or "X" pipe. The battle still rages over their benefits, but they're worth the install just for the effect on the exhaust tone.

Wrap Up

While this is far from the seminal work of reference on the 351M/400 Cleveland engines, you can see there's plenty of power to be had - you just gotta' know where to look for it. You may be asking yourself, "Why go through the grief? Why not swap in a big block?" Simple really. To extract a similar level of horsepower and torque, you'd still need to swap in a mildly built 429 / 460. Now when you compare the cost of building/swapping the big block to simply building the M/400, the money you save will pay for every mod we've listed here. All things being equal, a 460 will outpower it's little brother mod for mod. You can't argue with cubic inches - much. Yet a built 400 will provide disgusting levels of power. In the end, the 400 vs. 460 decision is yours alone.

Just remember, those Chevy guys get real nervous when they hear the word "Cleveland", and that's gotta' count for something!.