If you're a typical car crafter, one of the first performance-engine parts you bought was probably a dual plane intake manifold. A well-designed dual plane intake can improve torque, add horsepower, and make that otherwise stock engine look a little more aggressive. But it wasn't until we started counting did we realize the incredible variety of choices when it comes to choosing a dual plane intake manifold for a small block Chevy. We collected a 23-deep pile of dual plane intakes to continue with our small block Chevy dual plane intake comparison. The collection of manifolds could have been even larger, but we limited our test to the'55–'86-style bolt pattern. We bypassed both the Vortec intake and the '87 to mid-'90s intakes, on which the four center-bolt angles were altered. We mentioned that this intake comparison is part of a series of small block Chevy components testing we've completed. The first was a budget cylinder head-test in the Sept. '12 issue ("Eight-Budget-SBC-Head Shootout"), in which we wrestled eight less-than-$1,000 heads on our Slayer 350 small block Chevy. The following month, we looked at a bunch of inexpensive four-barrel carburetors ("The Great $299 Carburetor Shootout," Oct. '12). Most recently, in our June '13 issue, we completed our massive single-plane comparison ("The Great Intake Flog"), testing 19 intakes on our 406ci small block that is this month's test mule. A little teaser: If you were to combine the "winners" of these previous tests, you would have a fairly powerful combination—and that's exactly what you can expect us to do in an upcoming issue. That's our not-so-subtle way to keep you reading Car Craft.
Dual Plane Intake Test Engine
As we did with our single plane intake comparison, we are using the 406ci small block Chevy first introduced in the May '11 issue ("Build a 400ci Torque Monster For $2,500") and later rebuilt as "Build Big-Hammer Power" in the Dec. '11 issue. We've decided to call this engine Rodney Dangerfield because it gets no respect— only abuse. By the time we were done with this test, the 406 had slogged through more than 150 dyno runs with nary a whimper. The engine is basically the same as the one used in the June '13 single plane intake test, with a change to a milder Crane camshaft that is more in line with what would be used in a dual plane intake application. We've retained the same Crane Gold 1.6:1 roller rockers and 0.080-inch-wall pushrods. We also retained the TFS 215cc heads used in the previous test to ensure we could flow enough air to evaluate the intake manifolds and not the cylinder heads. Because we didn't expect to exceed 500 hp, we chose a more compatible 750-cfm Holley HP mechanical-secondary carburetor that worked well out of the box, needing only minor jet and air-bleed changes from time to time to ensure the air/fuel (A/F) ratio curve remained between 12.5 and 13.1:1. Finally, Westech's 13⁄4-inch dyno headers and 3-inch Flowmaster mufflers directed the exhaust.
Dual Plane Intake Test Procedure
With this many intake manifolds, we expected the competition would be very close. This demanded a very accurate test procedure to achieve best results. This meant that Westech dyno guru Steve Brulé had to control several variables, the most important of which was A/F ratio. Because we were using a carburetor, the A/F ratio is subject to significant swings based on manifold design. Carburetors also don't produce the same A/F ratio throughout the entire power curve. We made sure each test maintained an A/F ratio range within 12.5:1 and 13.1:1. That was the best we could do without custom-tuning the carburetor for each manifold. We also made sure the oil temperature was consistent for each test because cold oil can cost upwards of 5–10-lb-ft of torque and similar horsepower numbers. These requirements eventually dictated a test procedure in which we would subject each manifold to anywhere from three to five test runs until we had two curves within 0.5 percent. Then we averaged those two runs into a single curve. This eliminates an individual "hero" run from tweaking our results. In order to maintain timing accuracy, we used an MSD crank trigger with total timing set to 34 degrees, removing the variable of resetting the timing each time we changed manifolds. We also re-ran the first intake manifold tested at the end of the test to ensure that our 406 was still producing the same power. When the re-test gave us nearly identical results from the first run three days earlier, we knew our tests were as accurate as we could produce.
Overall, the dual plane intake test required the better part of three days, but we think accurate results were well worth the effort. Also, the TFS aluminum 215cc heads now have had nearly 50 intakes bolted to them, and those intake threads in the heads have held up just fine. Hero status is awarded to whomever does the heat-treating on those TFS heads! A big thank you to Fel-Pro for all the intake gaskets we blew through in this test and to Permatex for the big tubes of The Right Stuff RTV we used to keep the oil inside the engine. We've also used the Ultra Grey and Ultra Black with great results. Finally, thanks to Summit Racing for supplying a large pile of 3⁄8- and 1⁄2-inch Allen pipe plugs to seal up many of these manifolds. The Holley intakes came with plugs, though most of the other intakes do not.
Short Manifolds (Less Than 5.00 Inch Carb Pad Height)
|| TQ at 3,000
|Edelbrock Air Gap
|Weiand Street Warrior
|Weiand Street Warrior
|Summit Stage 1
While small-block Chevys are renowned for their interchangeability, Bow Tie engineers toss
There are two different carburetor bolt patterns for dual-plane intakes. The standard, squ
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