Words and Photos By Richard Holdener
Having recently run a single- vs dual-plane intake test, we always come away wanting the torque of the dual plane with the top-end charge of the single plane. Obviously, having our cake and eating it too is a difficult, if not impossible, proposition. This got us wondering if there is a better compromise to be had with carb spacers, instead of replacing the entire intake?
Given the open plenum, the single-plane intake is often less receptive to carb spacers than the dual plane. The reason for this is the dual-plane design is actually altered with the installation of a spacer, especially an open spacer that all but eliminates the divider inherent in the dual-plane design. Eliminate or reduce the wall on the divider and you can significantly alter or fine tune the shape of the power curve. Drag racers have been doing this for years, often with excellent results. The question now is, how much power can we unearth from a typical street/strip small-block Ford with a little fine tuning?
To test the effectiveness of carb spacers, we needed several things, including a test motor, a suitable dual-plane intake, and the necessary carb spacers. Taking these things in order, we ventured over to our local LKQ Pic-a-Part and snatched up a 5.0L Ford. Whether it came from a truck, Explorer, or passenger car (like a Mustang or T Bird) mattered little to us, as we planned on replacing the entire top end, including the camshaft. What we did want was a late-model, hydraulic roller motor, which ultimately came from a Ford Explorer (thnx Mark Sanchez).
The 5.0L was quickly stripped of its GT-40 heads and intake, along with the wimpy factory cam. Our early Explorer 5.0L did not yet possess the later GT-40P heads, so save the emails. In went our favorite 5.0L bump stick from COMP Cams, the XE274HR grind that offered .555/.565 lift split, a 224/232-degree duration split, and 112-degree lsa. The cam was run with the factory lifters, despite the significant amount of mileage.
With our new cam in place, it was time to improve the head flow. Replacing the stock iron heads was a set of 170cc 11R heads from Trick Flow Specialties. In addition to looking like externally like billet heads, the little 11Rs offered an impressive list of features. The heads featured full CNC porting of the intake, exhaustm and combustion chambers, revised valve angles (11 & 13 degrees), and a 2.02/1.60 stainless-steel valve package. The 11R heads were also available with 56cc combustion chambers to increase the static compression ratio over the typical 61cc chambers offered on stock or many after market 5.0L heads.
Available with different spring packages, we selected appropriate springs for our XE274HR hydraulic roller cam. The spring package employed on the 11R heads allowed our 5.0L to rev cleanly past 6,500 rpm. In addition to the heads, TFS also stepped up with a set of 1.6-ratio aluminum roller rockers and hardened pushrods. All this hardware was tucked under a set of Speedmaster aluminum valve covers.
To feed the 11R heads, naturally, we needed the proper dual-plane, which Speedmaster supplied in the form of a polished Eliminator intake. The dual-plane design promised ample torque production with plenty of peak power and delivered just that. The test mule was completed with an MSD ignition, Holley 650 Ultra XP carb, and Hooker 1 ¾-inch, long-tube headers.
Run with the dual-plane Eliminator, the modified 5.0L Ford produced 394 hp at 6,300 rpm and 370 lb-ft of torque at 4,300 rpm. Torque production exceeded 360 lb-ft from 3,700 rpm to 5,000 rpm. The first carb spacer from Wilson Manifolds to be run was a 1-inch, open design. Equipped with the open spacer, the peak horsepower number jumped to 402 hp at 6,400rpm, while the peak torque remained at 370 lb-ft, but at a higher 4,800 rpm.
After replacing the open spacer with the 1-inch, 4-hole design, the peak torque once again remained at 370 lb-ft, but it occurred back at 4,300 rpm. The peak power output checked in at 399 hp, meaning the 4-hole fine-tuned a little extra low-speed torque than the open, but was missing the extra top-end power. Such is often the case when tuning; a little more here often means a little less somewhere else, and we are fine with that.
Sources: LKQ, Lkqpickyourpart.com; ARP, Arp-bolts.com; COMP Cams, compcams.com; Holley/Hooker/Weiand, holley.com; MSD, Msdignition.com; Speedmaster, Speedmaster79.com; Trick Flow Specialties, trickflow.com; Wilson Manifolds, wilsonmanifolds.net