If you are looking for some extra power from your carbureted Ford, why not try carb spacers!

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?

Hardly a high-dollar crate motor, our 5.0L test mule came straight from a local LKQ Pic-a-Part. To prepare for the dyno session, the motor was stripped to the short block to facilitate a few performance modifications.

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).

First on the list was, naturally, a cam upgrade. COMP Cams stepped up with one of our 5.0L favorites in the form of the XE274HR grind. The COMP hydraulic roller cam offered a .555/.565 lift split, a 224/232-degree duration split, and 112-degree lsa. 

Working with the COMP cam was a set of TFS 11R 170 cylinder heads. Thanks to full CNC porting and revised valve angles, the TFS 11R heads offered some serious flow from the 170cc intake ports.

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.

The heads were set up with a hydraulic roller spring package to provide both sufficient coil bind clearance and rpm capability. 

To ensure we got all of the available cam lift, Trick Flow also supplied a set of 1.6-ratio aluminum roller rockers.

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.

Topping the TFS 11R heads was a dual-plane Eliminator intake from Speedmaster. Designed to promote a broad torque curve and plenty of peak power, the dual-plane design is the go-to intake for the vast majority of street and street/strip motor.

Fuel for our fire was fed by a Holley 650 Ultra XP carburetor. The 650 was sized perfectly for our little 5.0L Ford. 

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 eliminate the possibility of misfires that might ruin a perfectly good dyno session, MSD stepped up with some extra ignition energy in the form of a billet distributor and 6AL ignition amplifier.

We ran timing sweeps to maximize the power production of each combination, but each of the spacers ran best with 35 degrees of total timing. 

Ever present during testing was a set of 1 ¾-inch Fox-chassis Hooker headers and 18-inch collector extensions.

Run with the dual-plane Speedmaster Eliminator intake, the modified 305 Ford produced 394 hp at 6,300 rpm and 370 lb-ft of torque at 4,300 rpm. 

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.

First up was the 1-inch open spacer from Wilson Manifolds. The open design effectively eliminated the divider in the dual-plane intake. 

By contrast, the 1-inch, 4-hole spacer retained the divided plenum. 

We yanked the 650 Ultra XP carb to install the Wilson open spacer.

Run with the open spacer, the power output of the 5.0L increased to 402 hp at 6,400 rpm. The peak torque remained at 370 lb-ft, but this now occurred at 4,800 rpm.

Off came the Wilson open spacer to make room for the 4-hole design.

Run with the 4-hole spacer, the power output improved by 5-6 hp and never lost any torque compared to the intake alone. 

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.

302 Ford-Speedmaster Dual Plane vs Wilson Open Spacer Our COMP-cammed, TFS-headed 302 test motor was first run with the Speedmaster Eliminator intake then again after installation of the 1-inch Wilson open carb spacer. Run just with the dual-plane intake, the modified 5.0L produced 394 hp at 6,300 rpm and 370 lb-ft of torque at 4,300 rpm. Pretty decent numbers for a junkyard motor with sporty heads and a cam. After installation of the 1-inch open carb spacer, the peak numbers changed to 402 hp at 6,400 rpm, with the same peak torque number of 370 lb-ft occurring some 500 rpm later (at 4,800 rpm). The open spacer changed the dynamics of the divided, dual-plane intake and enhanced power higher in the rev range, but traded torque below 4,500 rpm. 

302 Ford-Speedmaster Dual Plane vs Wilson 4-Hole Spacer Having run the open spacer on the Speedmaster dual-plane intake, we decided to also try the 4-hole variety. The thinking was the 4-hole might improve power production at the top of the rev range like the open version, but without sacrificing so much torque below 4,500 rpm. The 4-hole certainly minimized the torque loss down low, and in fact offered every bit as much as the dual plane up to 5,100 rpm. From there out to 6,600 rpm, the 4-hole offered minor power gains of 5-6 hp, but not as much as the open version. 

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