Flowbench Variations
A flowbench is like a dyno and each can read a little differently. Most shops are honest but may not have properly calibrated equipment or the right accessories-including bore fixtures and radius plates-to ensure accurate results. The type of flowbench used is also important. "I know of a very well-respected shop using a homebuilt flowbench that uses an electric supercharger to move the air," Tony says. "The numbers on that particular bench were too stingy below 275 cfm, about right in the 300-350 cfm range, and optimistic above 400 cfm when compared to a SuperFlow SF600. Was it a useful tool in engine development for that particular shop? Very much so, but trying to compare numbers from that bench to other flowbenches would be somewhat of a useless exercise if you were really looking for exact comparisons." Even the same type of bench can read differently from one to another due to calibration differences, bore size, using clay versus a fixed-radius entry, and flowing the exhaust with or without a pipe. "Ultimately, flow numbers drive cylinder head sales, so buyer beware. Strongly consider getting your heads independently flowed on a known calibrated machine. It's far cheaper and less aggravating than trying to figure out why your car didn't dyno as high as you would have liked or get down the track as quickly as you hoped."
Intake Manifolds
"Don't forget that your cylinder heads' intake ports are at the mercy of your intake manifold design. If you really want to learn about your induction system, start flowing your heads with a manifold attached, and I promise it'll be a rude awakening and you'll think a bit differently about cylinder head design. It's all about the proper combination-that's a statement most engine builders will never argue with. The wrong intake choice can hurt the performance of a combination. For instance, our new Eliminator street heads flow so well that they're best matched with a race-style single-plane, such as an Edelbrock Super Victor 2925, versus a Victor Jr., which has been a popular street-oriented intake for some time. However, packaging constraints may be an issue, and there may not be sufficient hood clearance to run a larger, taller, and generally more effective race piece. For a killer street engine, don't overlook the modern, tall, dual-plane designs, such as Edelbrock's RPM Air Gap. These have come a long way and now barely give up any high-rpm power to a street-style single-plane, while managing to add 20-30 lb-ft across the bottom and middle of the power curve."