Plenty of folks have penned articles on carburetor spacers. Some work; some don't. So when we came across a series of spacers from HVH (High Velocity Heads), we were, to say the least, a wee bit skeptical. When it comes to conventional carb spacers for your Corvette, you might find a horsepower or two in some cases, move the power band around a bit and help distribution in other cases, but for the most part, there isn't much extra grunt available from a spacer. At least that's what we thought.
The truth is, the HVH spacer just might be set to revolutionize the carburetor spacer business. But let's back up for a minute. Who or what is HVH? Joe Petelle and his son, Keith, are HVH or High Velocity Heads. HVH may not be well known in the world of Corvettes, but it's another story in Winston Cup Racing, where they designed and ported heads, as well as intake manifolds from 1980 to 1992. Petelle and company designed a series of intake manifolds for Brodix and also created the layout for the Canfield big-block Chevrolet head. Currently, they primarily build carb spacers, but they also do limited amounts of custom cylinder head (yes, they do work on iron as well as aluminum heads and basically port anything that flows air).
The carb spacer designed and built by HVH is called the "Super Sucker." At first inspection it looks like a conventional four-hole spacer, but a closer investigation reveals it is a long distance from what one might term "normal." For example, the material is a plastic composite, and the spacer isn't simply cast. Instead it's actually CNC-machined. The area between the respective holes is carefully profiled. The top side (carburetor mount side) looks like any other four-hole spacer for a standard Holley flange, but the bottom (intake manifold side) is far different than anything you've probably seen before (see the accompanying photos). But how things look quite often don't equate to horsepower. The big question is - does it work?
We decided to test the Super Sucker on a SF901 dyno, using a very typical (for a street-driven Corvette) small-block Chevy. The engine in question was a relatively mild 355ci small-block Chevy with a set of mildly reworked small valve heads. If you check the volumetric efficiency of the engine, coupled with the brake specific, you'll find the engine is a reasonably efficient piece, considering it's docile inventory of components. Data was corrected for 29.92 inches Hg., 60-degree F dry air. The tests were done in a conventional A-B-A format (for the sake of simplicity, we haven't included the final back-up test; it pretty much matches the first test exactly). The baseline test results are as follows:
Brake Specific Fuel Consumption
5000 402.8 383.5 104.4 .49 5100 401.8 390.2 105.3 .49 5200 397.3 393.4 105.2 .49 5300 400.6 404.3 105.4 .49 5400 393.7 404.8 104.9 .49 5500 390.0 408.4 104.4 .49 5600 386.2 411.8 103.1 .52 5700 380.6 413.1 103.0 .51 5800 375.6 414.8 103.2 .51 5900 376.2 422.6 103.1 .50 6000 370.7 423.5 102.8 .52 6100 366.4 425.6 102.7 .50 6200 362.8 428.3 103.2 .51 6300 359.3 431.0 102.4 .52 6400 352.8 429.9 101.6 .52 6500 349.4 432.4 101.4 .53
Peak in baseline configuration was 432.4 hp at 6,500 rpm. Maximum torque was 402.8 lb-ft at 5,000 rpm.
The second test duplicated the first, with the only addition being the HVH "Super Sucker" carburetor spacer. Results are as follows:
Brake Specific Fuel Consumption
5000 413.2 393.4 105.0 .48 5100 405.3 393.6 104.7 .49 5200 398.8 394.9 104.1 .50 5300 402.1 405.8 104.6 .50 5400 396.9 408.1 104.4 .49 5500 390.4 408.8 104.5 .50 5600 387 .2 412.9 103.7 .50 5700 379.8 412.2 102.9 .50 5800 377.1 416.4 102.7 .51 5900 378.6 425.3 102.8 .50 6000 372.6 425.7 102.4 .50 6100 370.9 430.8 102.4 .49 6200 369.0 435.6 102.7 .51 6300 367.3 440.6 102.6 .52 6400 367.1 447.3 101.4 .51 6500 353.7 437.7 100.7 .52
As you can see, the small-block peaked at 447.3 hp at 6,400 rpm, while the maximum torque of 413.2 lb-ft occurred at 5,000 rpm. In comparing peaks, the Super Sucker added 14.9 hp and 10.4 lb-ft of torque (again at peak).
Our assumptions regarding carb spacers just went out the window. Keep in mind, this wasn't a 2-inch-tall spacer. It was a simple 1-inch-tall job; one that could fit under the hood of plenty of street-driven vintage Vettes. In theory, the 2-inch-tall model could have made even more power. So how in the world does this thing work? Keith Petelle of High Velocity Heads explains, "These spacers work by helping the fuel distribution. If you look at the bottom of the spacer, you'll see that the shape is different. The reason is, we wanted to improve the feeding of the outside runners on a single four-barrel manifold. The design picks up the air speed and gives it a specific direction. Finally, the plastic composite material insulates the carburetor. Plenty of people are skeptical. We've even had some used on high-horsepower race engines. Many people will think if they spent big money on a hand-fabricated intake manifold then they don't need a spacer. We've had some racers with very powerful engines see major gains. The spacers don't discriminate between expensive, high-horsepower engines and low-cost, low-horsepower street engines. They also work equally well on either small displacement engines or big ones. We typically see power increases in the range you found. We've seen more, but it really does depend upon the engine and the type of manifold used."
HVH machines all of their spacers from a proprietary solid plastic composite stock on Haas CNC mill equipment. They offer 1-inch and 2-inch-tall, four-hole spacers for 4150 Holley carburetors, 1-inch and 2-inch-tall, four-hole spacers for Holley Dominator carburetors, open 1-inch-tall spacers for Holley 4412 carburetors and two-hole, 1-inch-tall spacers for Holley 4412 carburetors. Spacers range in price from $85 to $105. Not cheap for a spacer, but in a well-sorted engine, 15 hp for 85 bucks certainly could be considered a bargain. In the end, our preconceived carb spacer notions were definitely wrong. There is power available from a carb spacer. It just goes to prove that in the quest for more performance, one can't take anything for granted.