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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.
With both displacement and compression taken care of, we turned to cam timing. When it comes to cam timing, the real choice is driveability versus power. Wilder cam timing (high-lift and long-duration) will result in higher peak power numbers and usually elevated power numbers higher in the rev range, but the cost is almost always low-speed torque production. The wilder the cam timing, the longer (in rpms) it takes for the motor to come on the cam and become efficient. The net result is lackluster performance lower in the rev range. Sure, the motor pulls like a freight train on the big end, but down low, it won't pull the sprouts off a Chia Pet. Obviously, compromise is in order when choosing a cam for a street motor, but our choice may surprise some. Rather than go with the typical hydraulic roller, we chose a solid roller profile. Not only did we choose a solid roller, but we chose one from Comp Cams that offered super aggressive ramp rates. The ramp rates were designed to maximize power production throughout the rev range-a feature definitely valuable on a street motor. Besides, the TK-series cam in question was actually leftover from my Engine Masters entry. Despite being a solid roller with aggressive ramp rates, the cam profile was designed to optimize power production below 6,800 rpm. The TK-series roller cam offered 0.688 lift (both intake and exhaust), a 249/253-degree duration split (at 0.050) and a lobe separation of 109 degrees. Though a high-lift, solid roller, this TK-series cam was smaller (in specs) than the largest XFI stroker hydraulic roller cam offered by Comp Cams (a popular choice for stroker Ford combinations).
One of the key ingredients in the power production of any motor is cylinder head flow. Working with the cam timing and intake design, the head flow helps dictate both how much (and where) in the rev range the motor makes power. Knowing that our large-displacement combination was going to need some head flow, we chose a set of CNC-ported Trick Flow Specialties' High-Port heads. The head choice was actually reason number two for my excitement with this build up, as the original TFS/KPI High-Port heads were my first venture into the world of performance aluminum heads for the 5.0L Ford (and Windsor applications).
While those original High-Port heads certainly offered a sizable jump in power over the factory E7TE Ford 5.0L castings, these fully ported versions from Trick Flow represented a giant leap in both technology and performance over the originals. Thanks to a combination of the 2.08/1.60 valves, CNC-porting, and careful hand blending, the Trick Flow High-Port heads offered impressive flow figures. The 225cc intake ports offered 335 cfm at 0.700 lift, while the exhaust flow checked in at 258 cfm at the same valve lift. These flow numbers at 0.700 lift were relevant since our TK-series cam offered 0.688 lift on both the intake and exhaust. The heads were set up with valvesprings to accommodate our near 0.700-lift roller cam and titanium retainers.
Working with the cam and heads, the intake manifold helps dictate the effective operating range of the motor as well. With plenty of head flow and our cam optimized for power production from 5,000 rpm to 7,000 rpm, we chose our intake manifold accordingly. Since the cam and heads were designed for power production higher in the rev range, we chose a single-plane intake manifold. The Edelbrock Super Victor seemed like a logical choice, but we didn't just install it out of the box and call it good. The intake was sent to the flow experts at Wilson Manifolds for custom porting work. The intake flow was optimized and the ports matched to the same 1262R intake gaskets used to size the entry of the head ports. In the interest of streetability (actually more due to the fact that the author forgot to secure a larger carb), the Wilson-ported Super Victor was topped off with a Holley 750 Street HP carburetor. A larger carb would certainly offer more peak power (we saw nearly 2 inches of vacuum present with the 750 Street HP), but we ran what we had. As the name would suggest, the Street HP Holley was actually a great choice for street use. The HP series is the standard of the industry for any performance carburetor, offering both impressive airflow and the tuning to back it up. The combination of the Wilson-ported Super Victor and Street HP-series Holley made for one serious induction system.
Naturally there were still a few odds and ends left to complete the motor. The ignition system consisted of an MSD billet distributor with matching cap, rotor, and plug wires. The 427 was run on the dyno using an MSD 6AL ignition amplifier and Denso Irridium spark plugs. The oiling system included a pan, pick up, and windage tray from Milodon, along with a high-volume oil pump and hardened oil-pump shaft. Additional features included a double-roller timing chain, 1.6 ratio Gold roller rockers from Comp Cams along with Hi Tech hardened pushrods. ARP supplied the 1/2-inch head studs, 7/16 rocker studs, and accessory bolt kit, while Fel Pro MLS head gaskets were employed to ensure adequate sealing. All testing was performed at Advance Product Engineering in Palmdale, California. The motor was primed and subjected to a computer-controlled break-in procedure using Lucas conventional oil, but we swapped over to the 5W-20 synthetic for all of the power runs. With jetting (75/80) and ignition timing optimized (35 degrees), the all-aluminum 427 stroker pumped out 615 hp and 545 lb-ft of torque. Best of all, the big-inch Windsor offered more than 500 lb-ft of torque from 3,850 rpm to 6,350 rpm, making for one sweet-for-the-street torque curve. Precious Metal was now ready to go in the engine bay-though we couldn't help but wonder how this motor might respond to a little boost? Maybe just one more dyno session is in order before we install this baby!