The SuperFlow 600 by virtue of its popularity has become the de facto industry-standard flow bench. This bench will easily test the big-block heads at 28 inches of water test depression at cfm levels approaching 600.
Flow Benches For Everyone
Todd Robertson, Georgetown, PA: About 10 years ago, I read an article in Car Craft, I think, about how to build a flow bench using vacuum-sweeper motors. The article was very descriptive and informative. With all the talk about cylinder heads and flow, I would like to build a flow bench for my own use. I need help locating this article. If you know about this article, please list the year and issue in which it is contained and also where I can get this information.
Jeff Smith: This is a great letter, Todd, because we love talking about flow benches. There were actually two very good stories in Car Craft on building flow benches. The first was written by Jim McFarland way back in the '70s. This multipart story dealt with much of the theory on how flow benches work and also explained how to build one. Much water has flowed under the bridge since then, although the theory still applies. The second story was written by CC Editor Emeritus Rick Voegelin. This two-part article ran in the Aug. '82 and Sept. '82 issues and delivered excellent information on flow-bench basics and how to construct your own bench. There is much more to the story now, since these are decades-old articles.
Let's cut to today. We'll give you two approaches to building a flow bench, and you can dive in as deep as you wish. But first, let's establish that you will not get much of an argument from the professional engine-building community that the SuperFlow 600 flow bench could easily be called the industry standard. This bench can create as much as 40 inches of water test depression (depending upon the size of the intake port you're testing) and flow as much as 600 cfm. These benches retail for $8,350 without SuperFlow's digital FlowCom attachment and are difficult to find on the used market because they are in such great demand.
The Performance Trends EZ Flow system can be as simple as this photo of testing a big-block Chevy head.
The first build-your-own-flow-bench kit we ran across is from a company called Mercdog Motorsports (mercdog.com). The company offers three kits ranging from the least expensive, which offers plans and blueprints plus computer software for data capture for a mere $30, up to the top-dog kit that runs $930 and gives you everything you need except the wood to build the cabinet and the vacuum-cleaner motors to create the air movement. The amount of pressure differential you need to test is completely dependent upon the number of electric motors you're willing to buy. For example, according to Mercdog, it will take six vacuum-cleaner motors to flow 500 cfm at 36 inches of water test depression. The performance-industry standard test depression is 28 inches, which means this bench can pull 600 cfm at this test level. That's a ton of air. Fewer motors mean lower cost but less airflow at the same test depression. If you are serious about flow-bench work and could potentially be testing large-port, big-block heads, you will need to be able to generate at least 400 cfm at 28 inches of water.
The second kit, from our pal Kevin Gertgen at Performance Trends (performancetrends.com), is a bit different. Gertgen's system is called the EZ Flow and uses any vacuum source (like a vacuum cleaner) plumbed through a simple PVC-pipe system with a calibrated orifice downstream of the cylinder head you're testing. The test unit also employs a "black box" that measures both a static test depression and velocity through the orifice. These data are recorded by the black box and sent to your laptop where they're converted into cfm of airflow at a given test depression. This system is a much quicker way to capture data and is intended to give the backyard tester a quick and easy way to compare flow data when making changes to his cylinder heads. The entire kit sells for $899.
One big variable in any kind of flow testing is the test depression. There is a simple math conversion that will allow you to convert flow cfm at 10 inches of water to cfm at 28 inches. However, most knowledgeable cylinder-head people will point out that a machine operating at 10 inches has resolution to record only major changes. Testing at 28 inches reveals many more subtleties. We've also heard from the guys at Dart that testing on their 1,000-cfm SuperFlow bench reveals even more things that their 600 bench doesn't see, even at the same test depression. It comes down to how much resolution you want to achieve.