Hooker supplied the necessary...
Hooker supplied the necessary long-tube Super Comp headers for our test. All the airflow into the motor must also find its way out.
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.
On the dyno, we relied on...
On the dyno, we relied on a complete MSD ignition including a Digital 7 ignition amplifier.
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.
Holley came through with one...
Holley came through with one of its HP series carburetors. The 750 HP was perfect for our application and worked well right out of the box.
On the dyno, the dual-plane-equipped...
On the dyno, the dual-plane-equipped 306 produced 427 hp and 394 lb-ft of torque. Even more important was that torque production from this motor exceeded 350 lb-ft from 3,200 rpm to 6,300 rpm.
Single VS. Dual-Plane IntakeThe...
Single VS. Dual-Plane IntakeThe graph clearly shows that the dual-plane intake offered more power than the single plane up to 5,300 rpm. Not only did the dual-plane offer more peak torque (394 lb-ft vs. 391 lb-ft), but the torque-producing nature of the dual-plane offered gains as high as 26 lb-ft at 4,200 rpm. Only at the top of the rev range did the single-plane design strut its stuff to the tune of an extra 9 peak horsepower, though the gains were as high as 12 hp at 5,900 rpm. On this mild application, the dual-plane intake would be the clear choice, as the extra torque offered through most of the rev range would be much more useful than the extra 12 hp in the last 800 rpm.
Torque production with the...
Torque production with the single-plane intake nearly matched that of the dual plane, but it did so some 500 rpm higher in the rev range. This shift greatly diminished the torque production below 5,000 rpm. The upside of the shift was a slight gain in peak power (436 hp versus 427 hp) compared to the dual plane.