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Single Plane Or Dual Plane Intake Upgrade
The Classic Battle Between A Single-Plane And Dual-Plane Intake.
The test motor was a bored 302 short-block from Coast High Performance equipped with an XE274HR Xtreme Energy (hydraulic roller) cam. Ensuring plenty of power was a set of 185 heads from the flow technicians at Airflow Research (AFR). The CNC porting offered by the AFR 185 worked well with the combination of cubic inches (306), cam timing, and compression of 9.8:1. Also present was a set of Hooker Super Comp headers, an MSD ignition, and Holley 750 HP carburetor. As indicated earlier, the combination is important, as the induction system must be chosen to work in conjunction with the optimized engine speed of the remaining components. Match the components correctly and you have a winner. Miss with just one component and the whole combination suffers.
The AFR-headed 306 was first run with the dual-plane Performer RPM. Equipped with such, the small-block produced peak power numbers of 427 hp at 6,100 rpm and 394 lb-ft of torque at 4,800 rpm. The dual-plane intake offered a healthy torque curve of more than 350 lb-ft from 3,200 rpm to 6,000 rpm, and more than 375 lb-ft from 4,200 rpm to 5,900 rpm.
After swapping the single-plane Victor Jr. intake, the 306 produced 436 hp and 391 lb-ft of torque. Despite the fact that the peak torque numbers were so similar, the overall power curves of the motor equipped with the two different intakes was decidedly different and would feel like as such from behind the wheel. The reason is that the peak of 391 lb-ft came at 5,300 compared to just 4,800 rpm for the dual-plane. The effective shift in the power curve meant that the dual-plane intake improved torque production up to 5,300 rpm over the single-plane, in some cases by as much as 26 lb-ft. From 5,500 rpm to 6,300 rpm, the single-plane offered minor improvements in power, the largest gain of 12 hp coming at 5,900 rpm.
The question on the table now is, which is more useful, an extra 20-25 lb-ft through most of the midrange or the slight advantage in high-rpm power? For this particular mild application, the dual-plane would be much better suited for street (and occasional track) use. Ideally, the single-plane intake would be combined with more of everything, more compression, displacement, and even wilder cam timing to maximize power production higher in the rev range.