One of the most difficult stories to do in the performance-magazine world is a direct component comparison. With any head-to-head comparison, there are going to be winners and losers. It's human nature to want to simplify a complex issue, such as the comparison of 19 different intake manifolds. When it comes to dyno testing, we naturally gravitate toward that romantic peak-horsepower number. The problem with picking a winner using a single test parameter—in this case, peak horsepower—is that one evaluator is rarely the best or only factor when making a decision on the "best." We believe choosing an intake manifold, or any high-performance engine component, is a complex decision based on a multitude of important factors, so we tried to cover all those factors with this test—as with all of Car Craft's most recent comparison tests, such as the small block Chevy (Sept. '12) and small block Ford (Feb. '13) head tests.
For this latest adventure, we assembled 19 small block Chevy single-plane intake manifolds and ran them all across a 550hp, 406ci small block Chevy. But that was just the start. We measured carb pad height because the manifold has to be able to fit under your hood. We measured plenum depth because that's important for making good power. We've also calculated average torque between 3,500 and 6,500 because that is the rpm band where these engines will spend the majority of their time during a quarter-mile run. We think average torque is the most important factor that we measured in this test. You will get tired of hearing that in this story because that's the hammer we're bringing. Apply a higher average torque, and it will accelerate any vehicle quicker. You might have a manifold that makes good peak horsepower, but if it loses torque in the middle rpm band, the peak-horsepower number is not nearly as important as the average power. The only instance where peak horsepower is really critical is if you have a close-ratio, eight-speed trans that can keep the engine within 1,000 rpm of its peak-horsepower rpm, but since we're not talking about Formula 1 here, that isn't really relevant to the average car crafter's car. So if you only take one thing away from this story, burn average torque into your memory bank.
The Test Engine
We wanted a stout engine capable of making good power to ensure that each manifold would be pushed to give its best. We decided to resurrect our 400ci small block Chevy that first appeared in the May '11 issue ("Build a 400ci Torque Monster for $2,500"), followed by its redemption story "Build Big-Hammer Power" in the Dec. '11 issue. We like to name our engines because it's easier keep them all straight, so this 406 is now dubbed Rodney, as in Dangerfield, because until now it has never received any respect. But after this marathon flogging, Rodney has earned his walkin' papers, as he endured us beating the snot out of him for more than 100 power pulls over four days, with never a whimper.
You may recall that Rodney spins an internally balanced 4340 Scat steel crank, Scat I-beam rods, and a set of Icon forged pistons. We upgraded the heads to a pair of TFS Super 23 aluminum castings to ensure we got the most out of each intake. The heads feature a 215cc intake port with 2.08/1.60-inch stainless-steel valves and roller springs capable of controlling the mechanical roller cam. The cam we chose is a Crane with sufficient specs to push the peak-rpm point up to 6,500 rpm but is still suitable for the street. We also added a set of Crane Gold 1.5:1 roller rockers and proper-length Crane pushrods to ensure a stable valvetrain. The point was to make the engine dead-reliable. Compression ended up at 10.1:1, which allowed us to run this engine on pump gas, though we ran Rockett Racing fuel to ensure consistent performance. We also wanted a big enough carburetor that it would not be a restriction, so we selected one of Holley's new Ultra HP 850-cfm carburetors that offered reliable fuel mixing and excellent consistency throughout the test. Only a few intake manifolds required mixture adjustments, and using an MSD crank trigger unit and distributor, we kept the timing rock-solid at 36 degrees so we wouldn't have to worry about resetting ignition timing each time we removed the distributor to swap an intake.
The 72cc as-cast chamber contains 2.08/1.60-inch stainless valves and is sealed with Viton
As we used new heads, we decided to also use a Fel-Pro MLS (multilayer steel) head gasket
We wanted to maintain the exact same ignition timing while swapping intakes, so we opted f