351M/400 Horsepower / Torque Gains

The 351M / 400 engines developed when engineers wanted an engine of mid size with the torque of a big block, and enough fuel/emissions efficiency to meet the growing governmental demands on the industry. The M/400 engines did not produce the torque to power combination that Ford had hoped for. Although they can certainly be improved upon.

Basically an engine needs to act like an air pump, the more efficient the air and fuel enters and exhausts the more power it will develop. The 351-400M will gain a very nice improvement in power and reliability with better Cylinder Heads, Camshaft, Oil Pan, Oil Pump and an improved exhaust.

Most often a  4x4 truck, the use of 2V heads are preferred over the 4V versions because of their superior low end torque. The big intakes of the 4Vs are excellent for high RPMs, but they hurt more than help most 4x4 applications. Ideally a small combustion chamber and intake runner would be the way to go, unfortunately, they were only available in Australia and are very scarce. Now we use the Aluminum Edelbrock Cylinder Heads which really bring this engine to life complimenting it the Air Gap Intake. There are some piston companies that offer more of a flat top piston that raises the compression from a dismal 8 to 1 up to 9 to 1 compression.

Using a larger camshaft is the next step. Not necessarily going with a huge duration and lift but enough to work for the 4 X 4 Truck. The valve springs must be matched up with this.

Oiling. Use a High Volume Oil pump with be better off as well.

Clevelands / Modifieds have a reputation for sucking down a lot of fuel. We prefer to use a 650Cfm Carb. in order to give it just enough fuel without going overboard to develop plenty of grunt Torque.

Exhaust

Stock manifolds are O,K, bolt on a set of headers 1-3/4 in. to 1-7/8in. primary tubes A 2 1/4 to 3 inch dual exhaust system with free flowing mufflers will result in a good match for this engine.

To get big time horsepower and torque, swapping over to a 460 is popular. The Big block bellhousing is the same as the M engine but the exhaust, pulleys, mounts and accessories are different.