What is the best intake for a street/strip stroker?

One of the most important decisions you can make about your performance build-up is the intake manifold design. Working in conjunction with the camshaft, and, to a somewhat lesser extent, the cylinder heads, the intake helps determine the effective operating rpm of the motor. Matching the power band of the cam and intake will produce optimum results. This, of course, assumes you have sufficient cylinder head flow. Mismatch the combination with one of the components and the result will be somewhat less than optimum power production. By this, we mean running a high-rpm cam with low-rpm intake (and vice versa). The power production of the intake will be signing off when the cam is just getting started. The result will be a lackluster power curve that excels at neither end of the scale.

For most high-performance, carbureted street (and strip) Ford applications, we normally recommend the dual-plane intake, as it offers a healthy dose of low and mid-range torque, without sacrificing much top-end power. Run on a 351W, a dual-plane (like the Edelbrock Performer RPM Air Gap) is tough to beat, but what happens when you increase the displacement and build a stroker?

Adding cubic inches to any combination can further complicate the induction needs. The reason for this is displacement tends to both tame the camshaft and increase the flow demands of the intake. An intake manifold originally designed for a 351-inch motor, for instance, will perform differently on a larger 408-inch stroker. All things being equal, the extra cubic inches will reduce the rpm where the motor makes peak power. A cam and intake combo that allows a 351 to produce peak power at 6,500 rpm will drop by several hundred rpm on a larger 408-inch motor.

The time-honored traditional of the single-vs-dual-plane intake usually ends up with peak power in favor of the single plane, but low-speed torque production in favor of the dual plane. This begs the question, will a single-plane intake designed to enhance power production higher in the rev range work better on a stroker application? To find the answer, we took a trip over to Westech Performance and spent some time on the dyno.

To run our single vs dual-plane intake test, we first needed a test motor. Since most intakes were built with stock displacement in mind, we wanted to see what happens when we run them on one equipped with extra inches. This obviously required building a stroker motor. Starting with a late-model, hydraulic-roller, 351W block, the boys from L&R Automotive machined it to accept our stroker assembly. The rotating assembly included a forged crank and 6.20-inch rods from Speedmaster combined with Mahle forged pistons. The 4.0-inch stroker crank was teamed with .030-over pistons to produce a finished displacement of 408c.i. Obviously, the stroker needed a suitable camshaft, and the XFI series from COMP Cams seemed like the perfect choice. Designed specifically for stroker Ford applications, we chose the XFI236HR-14. This cam offered .579 lift (intake and exhaust), a 236/248-degree duration split, and 114-degree lsa. The healthy XFI cam was neither a wild, race-only piece, nor was it a tame pussy cat, meaning it was perfect for our street/strip stroker.

Knowing extra displacement requires plenty of airflow, we installed a set of TFS Twisted Wedge 11R heads. The first thing you notice about the 11R heads is they look like they were carved from a solid chunk of aluminum. The billet finish adds plenty of wow factor to the build, but the good stuff is actually inside. The 11R heads featured 205cc intake ports (flowing 321 cfm), 66cc combustion chambers (also available in 56cc), and a spring package designed for the sub-.600 lift, hydraulic-roller cam. Thanks to revised valve angles and a modified chamber design, the 11R heads were serious power producers.

Finishing up the stroker were Fel Pro MLS head gaskets, ARP 1/2-inch head studs, and hardened oil-pump drive. The extra stroke can create additional windage, so we installed a complete oiling system from Milodon. The combination included pan, pick up, and windage tray, working with a standard volume oil pump. The Milodon components provided both extra power and a rock-solid oil pressure curve. The final components included TFS valve covers, a set of 1.6-ratio, Gold roller rockers, and hardened pushrods from COMP Cams.

The procedure for our test was a simple one: run the dual-plane, optimize the timing and air fuel, then repeat with the single-plane. For our dual-plane intake, we chose the Edelbrock Performer RPM Air Gap. Designed to enhance power production through the entire rev range, the Air Gap has been our go-to intake for almost any stock-displacement, 351W application, but would the extra stroke choke from a lack of airflow? That’s what we were here to find out.

After installation of the dual-plane Edelbrock intake, Holley 950 Ultra XP carburetor, and MSD distributor, the 408 produced peak numbers of 534 hp at 5,900 rpm and 543 lb-ft of torque at 4,300 rpm. As expected, the Air Gap offered a broad, usable torque curve, exceeding 500 lb-ft all the way out to 5,000 rpm. What the curves do not illustrate are the improvements in idle quality and throttle response (from improved signal strength) offered by the dual plane.

Next up was the single-plane intake from Trick Flow Specialties. Like the dual-plane Air Gap, the single-plane from TFS was installed with the MSD distributor (with identical timing curve) and 950 XP Holley. The single-plane design featured all eight runners joined in a common plenum.

Once the air/fuel mixture was optimized with minor jet changes, the 408 produced peak numbers of 570 hp and 541 lb-ft of torque. Run on this stroker, the single-plane increased both peak power and peak torque, but that wasn’t the whole story.

Single vs Dual-Plane Intake Test-408 Ford Stroker
In the age-old battle between single- and dual-plane intakes, this is usually what happens. The dual-plane makes more low-speed power, while the single-plane makes more top-end power. It would be ideal to have both, both the choice come down to where you want you power production. The dual-plane would certainly offer improved drivability and throttle response, but would obviously lag behind the single-plane when it comes time to run it hard. Run with the dual-plane, the 408 produced 534 hp and 543 lb-ft, but the single-plane upped the power ante to 570 hp and 540 lb-ft.

Far from choking our stroker, the dual plane offered better torque production down low, meaning (in this case) below 4,700 rpm. It is this cross-over point that causes enthusiasts to choose between the thumping low-speed torque offered by the dual plane and the rush of top-end power offered by the single plane. It would be nice to have both, but, in the end, it all comes down to where you favor power production.

Sources: ARP, Arp-bolts.com; COMP Cams, compcams.com; Holley/Hooker/NOS, holley.com; Milodon, Milodon.com; MSD, Msdignition.com; Speedmaster, Speedmaster79.com; Trick Flow Specialties, trickflow.com.