With the addition of the "Street Sweeper" carb spacer, the HVH dual-plane intake continued to make impressive power. The peak was 429.6 hp at 6,400 rpm while peak torque was 415.6 lb-ft at 4,700 rpm. As you can see, the spacer moved the power peak upstairs, with a gain of exactly 6 hp. Meanwhile, the torque peak went up by an impressive 9 lb-ft. Without getting into conclusions at this point, it's starting to look like this engine combination really "likes" the HVH dual-plane/"Street Sweeper" combination.
But we weren't quite done. For the next test, John replaced the HVH dual-plane with a tried and true Edelbrock Victor Jr. intake. Victor Jr.s are a stalwart in many forms of racing, and you see plenty of them on the street. How did the race-inspired single-plane fare against the dual-planes? Check out the chart.
It's easy to see that the race-inspired intake was much happier when operated in the higher-rpm ranges. It produced peak hp (421.4) at 6,200 rpm. Meanwhile, the peak torque was 399.2 lb-ft at 5,100 rpm. Compare these numbers to either of the dual-planes and it's becoming clear that a street small-block might really prefer a dual-plane intake arrangement.
But is this completely true? John bolted an HVH "Super Sucker" carb spacer (designed primarily for single-plane intake manifolds) to the Victor Jr. and came up with the following results.
John found a couple of horsepower with the spacer installed on the Victor Jr.
Peak was now 425.6 hp at 6,100 rpm (an increase of roughly 4 hp). Meanwhile, the torque peak with the spacer was 401.9 lb-ft at 4,900 rpm (a couple of lb-ft improvement, but at a slightly lower engine speed). We were close to the power produced by the HVH-Brodix dual-plane, but the torque was certainly down.
At this juncture, John decided to bolt on an HVH SP1 intake. The results of this test were remarkable:
Recognizing that the single-plane intake liked more rpm, Heida moved the rpm upward. He was rewarded with plenty of horsepower: The small-block produced a peak of 428.6 hp at 6,800 rpm coupled with 402.2 lb-ft of torque at 5,000 rpm. It was still short (although very slightly) of the best pull with the dual-plane intake, even when the engine speed was moved upward. To be quite honest, John tried a spacer on this combination, and it didn't really like it (no real power gain). Why not? Heida has a theory (and it's a good one): "The SP1 is a very well-developed intake manifold combination. It might work better with a spacer if the camshaft was different, but in these tests, the manifold worked perfectly right out of the box."
They Do Work As AdvertisedAs you can extrapolate from the above tests, it's easy to see that the manifolds perform pretty much as predicted by theory. A dual-plane simply makes more torque and power down low, but when the throttle is opened, the single-plane can eventually make comparable power (but it might take some work). Single-plane intakes can likely prove more powerful if the camshaft is revised to suit the intake.
So what's the point? In the end, a street-driven or street/strip machine will no doubt be a bunch happier with a dual-plane instead of a single-plane. On the other hand, if you're prepared to gear your car accordingly, fiddle with the camshaft and perhaps use a bit more converter stall speed, then the single-plane intake may eventually be superior. Name your poison. They both work. It's just that some intakes work better than others do.