The choice between single- and dual-plane manifolds for a small-block Ford comes down to a simple matter of engine operating speed.
Though choosing the proper intake is critical for maximum performance, even the word maximum means different things to different enthusiasts. Does maximum mean peak horsepower, peak torque or average power production through the entire rev range? Now toss in additional considerations like drivability, fuel mileage, and even torque converter compatibility, and the choice becomes even more difficult.
While we all like to brag about the peak power numbers produced by our Fords, the reality is that the vast majority of carbureted small-blocks spend most of their time well below that power peak. Truth be told, the vast majority of driving is spent below the torque peak, especially on street and street/strip engines.
While this intake test is indicative of the results for nearly every V8, the choice between single- and dual-plane manifolds for a small-block Ford comes down to a simple matter of engine operating speed. The dual-plane design — like the Edelbrock Performer RPM tested on our 347 Ford — was designed to enhance power production lower in the rev range, at least in comparison with the single-plane.
It is this flexibility and broad torque curve that makes the dual-plane ideal for many applications. Those in favor of the single-plane are quick to point out that the dual-plane will likely sacrifice power at top of the rev range. For high-RPM, race engines, designed to produce power at the top of the rev range, engine builders almost always choose the single-plane. High-rpm race engines are a small segment of the performance population, and for most stock, mild or even performance buildups, the dual-plane might well be a better choice, but what better way to find out than by putting them to the test?
Rather than select a stock or even mild 5.0-liter Ford, we really wanted to push those intakes with the power curve produced by a stroker engine.
The production 5.0-liter engine features a 4.00-inch bore with a 3.00-inch stroke. By contrast, the 347 features a .030-inch overbore (4.030 inches), and 3.40-inch stroke. The stroker crank and 5.40-inch forged rods came from Speedmaster, while the forged, flat-top pistons were supplied by JE.
Rounding out the short-block is a COMP XFI236HR cam delivering .579 lift, a 236/248-degree duration split and 114-degree lobe separation angle. COMP also supplied a set of drop-in hydraulic-roller lifters, a double-roller timing chain and hardened pushrods for our stroker. A Melling high-volume oil pump, an ARP oil-pump drive, and a factory oil pan rounded out the short-block.
To ensure the stroker short-block and COMP XFI cam had plenty of airflow, we installed a set of ProMaxx aluminum cylinder heads. The 210cc ProMaxx heads feature intake ports that flow over 320 cfm. In addition to full CNC porting, the heads utilize 60cc combustion chambers and a 2.08/1.60, stainless-steel valve package.
Given the flow rate and port volumes, these heads were likely a better choice for a 600-horsepower stroked Windsor with over 392 cubes, but we knew there would be no shortage of airflow for our 347.
The one thing missing from the supplied heads was a spring package. After checking the required installed height, spring pressure and maximum lift, we settled on a set of springs (PN 939), spring seats (PN4771), and titanium retainers (PN 732) from COMP Cams. The combination provided plenty of coil-bind clearance for our .579-lift XFI cam, along with the ability to rev safely past 6,500 rpm, without fear of valve float. The rpm capability was important, as the single-plane combination wanted to make peak power at 6,500 RPM.
With the long-block essentially complete, all that was necessary were a few finishing touches. First off, L&R Automotive internally balanced the rotating assembly, so we installed the appropriate damper from Speedmaster. To ensure the damper stayed in place, we secured it with an ARP damper bolt.
Tested on the ProMaxx-headed 347 stroker, the intake teste once again illustrated the single/dual-plane conundrum. Judged solely by peak numbers, the single-plane Victor Jr. bested the dual-plane Performer RPM, by producing 441 horsepower to just 434 hp, but is that the whole story? Looking elsewhere on the curve, dual-plane intake offered more power up to 4,900 rpm. In most acceleration contests, the dual-plane would have the initial edge and the single-plane would be forced to play catch-up, to say nothing of how often you use the power above and below 5,000 rpm. The torque curves echo what we saw in the power curves, with a hefty torque advantage going to the dual-plane. As much as we’d all love to have the torque of the dual-plane with the peak power of the single-plane, life always comes down to a choice. Will you use the extra 25-30 lb-ft of torque more often than the 15 horsepower out at 6,700 rpm?
Taking the Test
Speaking of power, we first hit the dyno with the Edelbrock Performer RPM dual-plane intake atop the 347. As indicated, the this intake was designed to enhance torque production lower in the rev range than the single-plane Victor Jr., and that is exactly what happened.
Run with the dual-plane, the ProMaxx-headed 347 stroker produced 434 horsepower at 6,200 rpm and 412 lb-ft of torque at 4,400 rpm. Torque production with the dual-plane exceeded 400 lb-ft from 3,800 rpm to 5,100 rpm, making for a broad, usable torque curve.
Moving on to the single-plane Edelbrock Victor Jr. intake, the peak horsepower output jumped to 441 horsepower at (a slightly higher) 6,500 rpm, but peak torque dropped to 405 lb-ft at (again, higher) 5,000 rpm. The single-plane offered more power above 4,900 rpm, but lost out below that. The plane truth is that the choice between the two intake designs (as always), comes down to where you favor the power production. The upside is no matter which one you choose, Edelbrock has you covered.