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ManifoldsJuly - August 2002 Motor State Performance Report Article By Jim Kaekel, Jr.

A QUICK LOOK AT THE INTAKE MANIFOLD

What's in a name, anyway? With names like Street Dominator, Performer, Stealth, X-Celerator and Torker, an enthusiast would likely think he was ordering up the latest action/adventure movie on DVD rather than an intake manifold. Design nomenclature aside, Edelbrock offers over fifty different street and racing manifolds for carbureted small block Chevrolets alone. Add intakes for other GM, Ford and Chrysler applications, and then add other manufacturers like Holley, Weiand and Offenhauser to the mix and it's easy to see why choosing a manifold is an involved process. The fact that there are lots of choices should be a solid indication of one thing: a good intake manifold will definitely improve performance.

Manifolds are generally manufactured in two basic styles: SINGLE PLANE and DUAL PLANE. Each design has a distinctive appearance and yields different performance characteristics.

DUAL PLANE MANIFOLDS provide maximum low- and mid-range power by using two separate plenum chambers to feed two different induction paths. Dual plane runners are long, but relatively small in diameter to enhance low- and mid-range power. Because of their small diameters, dual plane runners limit the amount of top end horsepower that can be produced. Dual plane intakes shine on the street, though, where they can provide plenty of usable horsepower all the way up to 6,000 RPM.

SINGLE PLANE MANIFOLDS, with large diameter, relatively short runners, provide outstanding high RPM horses, but at the sacrifice of low-end power. Single plane runners can each draw air/fuel mixture from all four of the carburetor venturii, so a greater volume is drawn into each of them. A single plane manifold produces excellent top-end power and works best on race cars. Use on a street vehicle should generally be avoided unless the car in question is lighter than 2,500 pounds and is fitted with a suitable camshaft, lower rear end gears and a higher stall speed torque converter. Single plane intakes are quite popular on lightweight street rod coupes and roadsters with open engine compartments because of their more competition-oriented appearance.

SELLING THE INTAKE MANIFOLD

The first inclination on the part of most potential intake manifold customers is to apply "More's Law"... if some is good, MORE's better, and too much is just enough. While this theory may garner some merit in certain quarters, it just won't work for intake manifold selection. A tunnel ram sporting two beefy four-barrels may look really "bitchin" standing tall above the cowl on the old '32 three-window, but unless the owner can figure out a way to buzz better than five grand in city traffic, looks are the only benefit he'll experience. For the best driveability, we suggest strongly recommending the single carb approach, with an appropriate intake matched to the car's potential.

A point worth of consideration is that even most drag racers have changed their thinking in recent years with regard to intakes and carbs. Most strong running bracket cars are turning in very impressive elapsed times with single carb, high-rise manifolds with large runners and carbs in the 900-1100 cfm range. By way of an example, consider the single carb, single plane equipped Mopar wedge that can consistently outrun its dual-quad, crossram equipped counterpart. It's tough to fault modern technology where intake design is concerned.

Keep in mind that what we are primarily trying to avoid here is sending a hot rodder out into the real world with a hopelessly mismatched setup like a 850 cfm carburetor and a single plane intake bolted to his 305 small block-powered Caprice. For stock applications, the "bread and butter" dual plane, small carb treatment will yield outstanding results with no other modifications. Beyond this, bigger carbs and more exotic intakes are only going to benefit the engine if a "package" approach is used. By packaging a larger carb and intake with other suitably matched performance enhancing components like cams, lifters, rocker arms, and timing kits, a much stouter output can be realized. Isn't this what hot rodding is all about? Good luck... and GREAT SELLING!

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