Probe Racing supplied the...
Probe Racing supplied the necessary forged pistons for our 400M build up. Basically flat-top, 351 Cleveland slugs, though still down in the hole nearly 0.060, the flat-top pistons nonetheless increased the static compression ratio of the 400M over the factory dished pistons.
For our buildup, we started with a fresh short-block supplied by Demon Engines. L&R Automotive was kind enough to transform a used core into a workable short-block using a combination of factory and aftermarket components. To minimize costs, we reused the stock block, crank, and rods, but the block and factory connecting rods were treated to some much-needed machine work. The block was bored 0.030 over to accept a new set of flat-top forged pistons.
Lucky for us, the compression height of the 400M pistons is very close to the 351C. The slight difference (1.624 versus 1.650) between the factory 400M pistons and our forged 351 Cleveland pistons from Probe Racing decreased the deck clearance and helped increase the static compression ratio.
The forged flat-top pistons were installed on the stock (reconditioned) rods. Aftermarket rods for the 400M are few and far between since the tall-deck 400 motor requires the use of 6.58-inch rods (compared to 5.78 for the 351 Cleveland). The factory rods were treated to beam polishing and a set of ARP rod bolts. After all, we planned on running the motor well past 3,600 rpm (the power peak of the original motor). Naturally the 400M short-block also received new rings and bearings courtesy of Demon Engines and L&R Automotive.
Here is our freshly painted...
Here is our freshly painted 400M short-block ready to accept the stock cam and two-barrel heads.
In factory trim, the 400M produced peak power at just 3,600 rpm and offered its torque peak at 2,000 rpm. Since horsepower is nothing more than a mathematical representation of where there the torque curve occurs, shifting the torque curve higher in the rev range will greatly increase the peak horsepower number. We chose not only wilder cam timing compared to stock, but further upgraded the power potential by swapping out the hydraulic flat-tappet cam for a pair of solid roller profiles.
While solid rollers are usually reserved for race motors, we first chose a street roller from Crower Cams. With slightly milder ramp rates than a race roller, the street roller was much more parts friendly and would require less maintenance over the long haul. The roller profile allowed us to have much more aggressive ramp rates than a flat-tappet grind. What this meant was that we could have our power with less duration (measured at 0.050). Basically, the solid street roller allowed us to make more power with less cam.
The Crower street roller offered a 0.570-/0.572-lift split, a 234-/244-duration split (at 0.050) and a 110-degree lobe separation angle. Crower also supplied the matching solid-roller lifters to work with the cam. It is certainly possible to exceed the 500hp mark using a solid or even hydraulic flat-tappet cam, but you'd have to run a minimum of 10-15 degrees more duration than the roller to make equivalent power.
Making sure we maximized the cam profile was a set of 1.73:1-ratio aluminum roller rockers from Comp Cams. Naturally the factory stamped steel rockers (non-adjustable on the 400M two-barrel heads) were not adequate for our needs, nor would they work as the Pro Comp heads were set up to accept rocker studs and guide plates.
Solid-roller cam choice No. 2 came from the Ford cam experts at Cam Research Corp (www.camresearchcorp.com) in Englewood, Colorado. You might recognize the Cam Research name from the Engine Masters competition. These guys know Ford cam timing and only bad luck has kept them out of top finishes, if not outright wins in the competition.
After explaining our 400M combination the staff first asked about our choice of static compression ratio. Even after swapping the factory dished pistons for flat tops and reducing the combustion chamber size, we were still left with a static compression ratio of just under 9.5:1. Since this wasn't ideal for performance use, Cam Research designed a profile to optimize performance with the reduced static compression in the desired rpm range.