Bolting on the right set of heads can make or break your stroker Ford.

Words and Photos By Richard Holdener

The list of things that change the power output of any motor is endless. Check out Facebook, the forums, or any gathering of gear heads and you’ll find any number of esoteric discussion topics, ranging from merge collectors to rod ratio. Everyone has their favorite power adder, tenacious tune, or top-secret cam profile, but the truth is, the success of any combination is determined by its compatibility.

Ford fanatics may argue the point, but their wonder Windsor (like all lesser motors), is nothing more than a glorified air pump. Once we come to grips with that fact, we immediately recognize the power output of said pump is a function of the amount of air it can process. The word process is important here, as air through (into and out of) the motor is decidedly different than simply measuring the airflow potential of cylinder heads or an intake manifold. Getting the Windsor pump to process that air effectively requires all the individual components working in harmony. This occurs when all of them are designed to operate effectively over the same rpm range.

Don’t get us wrong, things like rod ratio, collector design, and the air/fuel curve all play a part in power production. They just take a back seat to the three major contributors, namely the heads, cam, and intake, or big three as we like to call them. The big three determine not only the peak power and torque outputs, but the overall shape of the power curves, from idle right through to the redline. This test, on the 210cc heads from ProMaxx, was designed to illustrate what happens when you miss on just one of the big three.

COMP Cams also stepped up with a double-roller timing chain, retro-fit hydraulic roller lifters, and hardened pushrods. Note the ARP damper bolt used to secure our neutral Speedmaster damper.

We previously ran these ProMaxx heads on a smaller 347 stroker, but with 210cc intake ports (that flowed over 320), the heads were better suited to a larger, more powerful stroker combination. Credit for those impressive flow figures goes to full CNC porting, including the 60cc combustion chambers and a 2.08/1.60 stainless-steel valve package. To complete the heads, (they were shipped bare with valves), we installed 939 springs, 4771 spring seats, and 732 titanium retainers, all from COMP Cams.

With the test heads at the ready, we also prepped a set of stock iron, E7TE (5.0L Ford) heads. The heads were upgraded with a spring package to allow for the high-lift, hydraulic roller cam. The stock heads were also run with a set of guided, 1.6-ratio roller rockers in place of the factory units. No changes were made to the ports of the stock heads. Both sets of heads were applied to our stroker test motor, meaning a 351 Windsor-based 393.

The 393 short block featured a forged crank and rods supplied by Speedmaster, along with a set of forged, flat-top pistons from JE. The pistons featured sufficient valve reliefs to allow for our healthy XFI cam profile and a set of Total Seal rings. Since the 393 was sporting extra inches, we chose the larger of the two XFI stroker grinds. The XFI248HR cam offered .608 lift, a 248/258-degree duration split, and 114-degree lsa. COMP also supplied a set of drop-in, hydraulic-roller lifters, hardened pushrods, and a double-roller timing chain. The short block was sealed up using a factory oil pan, Mellings HV oil pump, and ARP oil pump drive. The heads were secured to the 393 short block using Fel Pro 1011-2 head gaskets and ARP head studs. The COMP 1.6-ratio Ultra-Gold roller rockers were covered with a set of Speedmaster cast-aluminum valve covers.

With the long-block portion of our stroker test motor complete, it was time to install our damper, induction, and ignition systems. First up was an internally balanced damper from Speedmaster (with ARP mounting bolt), followed by a single-plane Victor Jr. intake from Edelbrock (sold by Ford Motorsports). Feeding the high-rpm, single-plane was a Holley 950 Ultra XP carburetor. The final touch was an MSD distributor and ignition amplifier.

Run with the ProMaxx heads, the 393 stroker produced 558 hp at 6,400 rpm and 512 lb-ft at 5,000 rpm. Peak power was raised by 171 hp and occurred 1,400 rpm higher, while peak torque jumped by 51 hp and occurred 1,500 rpm higher.

Equipped with Hooker headers, the 393 stroker was run first with the stock iron 5.0L heads. Equipped with the E7TE heads, the 393 produced 387 hp at just 5,000 rpm and 461 lb-ft of torque at 3,500 rpm. We knew the stock heads were restricting the combination, but didn’t know how much until we installed the CNC-ported heads from ProMaxx. After installation, the power output of the 393 soared to 558 hp at 6,400 rpm and 512 lb-ft of torque at 5,000 rpm.

With the right heads, the peak torque occurred where the stock heads made peak power. All told, the head upgrade was worth 171 hp, a clear indication how important it is to choose the right headgear for your stroker.

393 Stroker Head Test-Stock 5.0L vs ProMaxx 210
What looks like the result of adding a supercharger or pair of turbos, is actually from a simple head swap. Replacing the stock E7TE 5.0L Ford heads with the CNC-ported 210s from ProMaxx resulted in huge power gains. Truth be told, the 393 stroker was much better suited to the flow offered by the ProMaxx heads, as the stock versions were designed for a fuel-injected 302 rated at just 225 hp! Test results always look amazing when you replace the one bottleneck in the system, but it does illustrate the importance of planning ahead when choosing performance components for your stroker Ford application.

Sources: COMP Cams, compcams.com; Edelbrock, edelbrock.com; Holley, holley.com; JE Pistons, jepistons.com; Lucas Oil, lucasoil.com; MSD, msdignition.com; ProMaxx Performance, promaxxperformance.com; Speedmaster, speedmaster79.com; Total Seal Rings, totalseal.com