Words and Photos by Richard Holdener

Having recently run a single- versus dual-plane intake test, the question that always follows is whether there is a better compromise available through carb spacers - rather than replacing the entire intake. The dual-plane design responds differently to spacers than a single-plane, because the spacer can alter or eliminate the divider that defines the dual-plane's character. Drag racers have used this technique for years. The question here is how much measurable difference a spacer makes on a typical street/strip small-block Ford.

The Test Motor

The 5.0L test mule came from a local LKQ Pic-a-Part. It was stripped to the short block to prepare for a series of performance modifications. Whether the motor originated from a truck, Explorer, or passenger car was secondary - the priority was a late-model hydraulic roller short block. This one came from a Ford Explorer.

Cam and Heads

The factory cam was replaced with a COMP Cams XE274HR hydraulic roller grind: .555/.565 lift split, 224/232-degree duration split, and 112-degree lobe separation angle. The cam was run with the factory lifters despite significant mileage on the motor.

Replacing the stock iron heads was a set of Trick Flow Specialties 11R 170 cylinder heads. Features include full CNC porting of intake, exhaust, and combustion chambers, revised valve angles (11 and 13 degrees), a 2.02/1.60 stainless-steel valve package, and available 56cc combustion chambers for increased static compression over the typical 61cc aftermarket offering.

The spring package on the 11R heads allowed the 5.0L to rev cleanly past 6,500 rpm. TFS also supplied 1.6-ratio aluminum roller rockers and hardened pushrods, all tucked under a set of Speedmaster aluminum valve covers.

Intake and Supporting Components

Feeding the 11R heads was a polished Speedmaster Eliminator dual-plane intake. The dual-plane design delivers broad torque production with strong peak power - the standard choice for the majority of street and street/strip applications.

Fuel delivery came from a Holley 650 Ultra XP carburetor, sized appropriately for the 302's displacement. Ignition was handled by an MSD billet distributor and 6AL ignition amplifier. Exhaust exited through 1 3/4-inch Fox-chassis Hooker headers with 18-inch collector extensions.

Timing sweeps were run to maximize power for each configuration. Each spacer combination ran best at 35 degrees of total timing.

Baseline: Speedmaster Eliminator Intake Alone

With the Speedmaster Eliminator dual-plane intake and no spacer, the modified 302 produced 394 hp at 6,300 rpm and 370 lb-ft of torque at 4,300 rpm. Torque exceeded 360 lb-ft from 3,700 rpm to 5,000 rpm.

Test 1: Wilson 1-Inch Open Spacer

The 1-inch open spacer from Wilson Manifolds effectively eliminates the divider in the dual-plane intake, converting it closer to a single-plane design. Results: peak horsepower climbed to 402 hp at 6,400 rpm. Peak torque held at 370 lb-ft but shifted up to 4,800 rpm. The open spacer enhanced power higher in the rev range but traded torque below 4,500 rpm.

Test 2: Wilson 1-Inch Four-Hole Spacer

The 4-hole spacer retains the divided plenum, preserving the dual-plane character while adding intake runner volume. Results: peak torque returned to 370 lb-ft at the original 4,300 rpm. Peak power reached 399 hp - 5 hp over baseline. The 4-hole matched or exceeded the intake-only torque curve up to 5,100 rpm, then added 5-6 hp through 6,600 rpm without the low-end trade-off of the open design.

The Takeaway

Both spacers delivered measurable gains on the Speedmaster Eliminator intake. The open spacer is the choice for builds that prioritize peak horsepower and spend time at higher rpm. The 4-hole is the more balanced option for street/strip applications where low-speed torque matters as much as top-end power. As with most tuning decisions, the right spacer depends on the application - a little more in one range typically means a little less in another.

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