The second test duplicated the first, with the only addition being the addition of an HVH "Street Sweeper" carb spacer (this is a new configuration spacer that is designed specifically for street-style, dual-plane manifolds-more in the accompanying photos). The dyno results might surprise you.
The torque peak was 408.6 lb-ft at 4,600 rpm. Meanwhile, the horsepower jumped (over the baseline) to 419.7 at 6,200 rpm. The addition of the HVH "Street Sweeper" spacer added 7 hp to the Performer RPM intake, as well as 8 lb-ft of torque. You can see by examining the charts that the spacer allowed John to take the engine higher in the power band. It continued to pull at 6,400 rpm. Just as interesting was the brake specific fuel consumption. It dropped by a considerable margin. In simple terms, the addition of the spacer made the baseline combination more efficient.
In the next test, John removed the Edelbrock Performer RPM and installed an HVH dual-plane intake manifold. In this test, the dual-plane was run without a spacer.
As you can see, the small-block peaked at 423.6 hp at 6,200 rpm, while the maximum torque of 406 lb-ft occurred at 4,600 rpm. In comparison, the HVH dual-plane was slightly more efficient and made more power (actually quite a bit) than the baseline intake. It also made more power and a wee bit less torque than the Edelbrock Performer RPM with the HVH "Street Sweeper" carb spacer installed. You'll also note that Heida took the engine up slightly in rpm, simply because it seemed to like it (note that it was still climbing in peak power at 6,200 rpm).
At this point, John pulled off the carburetor and added a HVH "Street Sweeper" carb spacer. Results are as follows: