Muscle Mustangs & Fast Fords
All-Aluminum 427 Street Stroker Testing
Building And Testing An All-Aluminum 427 Street Stroker
In the performance world there are certain monikers or names that have great meaning. For instance, you can say Hemi, Shelby, Boss, or Terminator and no explanation is needed.
Additionally, some engine displacements fall into this category. For whatever reason, the number just sounds cool. One such is 427, which has a magical ring to it. I must admit, I was very excited about this all-aluminum, 427-inch Windsor build. First off, this was the first time I was involved in the build-up and testing of an all-aluminum, small-block Ford.
The idea behind the build was to do more than satisfy my own curiosity, however, as Project Precious Metal was designed to provide the very best of both worlds-the light weight of a standard 302 with the power of the larger (but usually heavier) 351W. Naturally, it's possible to build a 302-based stroker, an all-aluminum version no less, but even in its largest iteration, it will never offer the torque production of its big brother. Even if you combine a 4.125 bore with a typical 3.40-inch stroker, the 302-based motor will only just exceed 360 cubic inches. Without even trying, this all-aluminum monstrosity displaces 427 cubic inches. It's possible to go beyond this displacement, but the combination of the 4.125-inch bore and the 4.00-inch stroke was a hassle-free, ready-to-run street combination that promised plenty of power.
Precious Metal became a reality when the good folks at Dart stepped up to supply a magic aluminum block. We say magic because there must be alchemy involved when you can literally add lightness. Knocking off serious chunks of weight is the same as adding horsepower.
Not only will weight reduction improve acceleration, it performs the same magic on both handling and braking. In one fell swoop, dropping weight was akin to adding sticky R-compound tires, a set of Baer brakes, and a supercharger. OK, so that may be an exaggeration, but given the improvements in all aspects, less weight improves the dynamics even more than an increase in power. Making the situation even more impressive is the fact that the weight improvement offered by the aluminum block is up front, where the weight really needs to come off in a (typically) nose-heavy Mustang. Shedding the pounds alters both the power-to-weight ratio as well as the front-to-rear weight balance by effectively shifting it rearward. This further improves both handling (by reducing understeer) and braking (allows use of more rear brake bias). For a Mustang (or other fast Ford) owner, an aluminum block is a gift from the gods.
Now that we have extolled the virtues of less weight, we need to check out the other side of the formula, namely the power portion. A weight reduction is all well and good, but more power never hurts, especially when that power adds basically no weight. Since the Dart 351 block was set up to accept any 351-based crankshaft, we chose to step right past the standard 351W stroke to something offering a bit more cubes. Since displacement adds horsepower and the additional weight of a stroker crank versus a standard 351 stroke was negligible (and located low in the chassis), we decided on a 4.00-inch steel crank from Coast High Performance (CHP). In fact, CHP supplied the entire reciprocating assembly, from the forged steel stroker crank to the forged rods and pistons. In keeping with our theme which states, "more power is better," we decided on a set of flat-top pistons (which enhances flame travel over dish or dome pistons). The use of flat-top pistons on a motor of this displacement usually means you have a static compression ratio exceeding 12.25:1. Hardly considered pump-gas friendly, the static compression ratio was reduced to a street-friendly 10.3:1 using a rather large combustion chamber, but more on that later.