OK, we rodders are "tinker junkies" just itching to make this winter's mod to our street rod powerplant. Those of you with a recent GM Performance Parts crate motor with the late-model Vortec heads or those of you who have retrofitted your small-block with this excellent street-performing cylinder head have some intake manifold options that were heretofore minimal at best. What can we do in the off-season before this year's rod run season is upon us?
Well, if one carburetor is cool, then two must be rodding heaven-or something along those lines. The dual-quad setup has always found a willing home on a street rod engine; it not only looks good, but the performance can be one visceral seat-of-the-pants experience in your street rod.
We are going to take a look at the manifold and carburetors coming in either as-cast finish or the EnduraShine Finish. (Five-digit part numbers ending in "4" signify EnduraShine Finish, while the absence of the number 4 is as-cast.) The EnduraShine Finish is something Edelbrock is very proud of, and when you see it in person, you too will understand. The bright silver coat chrome finish has powdercoated durability and will resist discoloration from heat while the clear topcoat enhances the polished aluminum look. It is a three-step vacuum metalizing process that includes a basecoat, aluminum coat, and a clear topcoat to ward off abrasion and features chemical resistance. Oh yes, did we mention that it gives a maintenance-free polished aluminum appearance? Well, you do have to wipe it off for it to achieve the optimal look!
The carburetor of choice for the RPM Air-Gap manifold is the Edelbrock Thunder Series AVS carb. They are designed and calibrated with the street in mind, which means you will get the performance, tuneability, and drivability that you must have in a dual-quad setup that is to "live" on the street. This carb features the Qwik-Tune secondary air valve and is based on a two-piece body. They are unaffected by engine backfires, which means there are no power valves to blow out, and the rods can be changed in seconds without carburetor removal or fuel draining. Edelbrock has found in testing that these carburetors have the ability to "hold a tune"; once they're tuned, they stay tuned.
The Qwik-Tune adjustable valve secondary allows you to adjust the secondaries with common handtools and no springs are required. It doesn't matter whether your street rod tips the scales in the "sumo" category or you have a "lightweight" roadster, you can tune easily and quickly. According to Edelbrock, "Counterweighted secondary carburetors utilize a heavy, non-adjustable 'counterweight' that relies solely on the velocity of the air coming through the secondary venturis to roll open the secondary air door. Under certain conditions, a delay or stumble can occur when transitioning between the primary and secondary circuit at wide-open throttle (WOT). This is due to the velocity not being able to roll the air door open fast enough. This condition is virtually eliminated with the AVS feature."
The carbs also feature float levels set at Edelbrock, and are reported to rarely need adjustments, thereby creating a simple "bolt on and run" performance carburetor; they also feature two-step metering rods for independent tuning of cruise and power circuits; change jets, adjust floats, or replace needles and seats without draining fuel. An optional single- or dual-fuel inlet allows for flexibility when plumbing the fuel line.
Before you tear into your engine, here are a few tidbits to take note of: You should round up some Gasgacinch (#9300), sold through Edelbrock, which comes in a 4.0oz container. Now the Edelbrock RPM Air-Gap Dual Quad manifold and carburetor kit comes with gaskets, but should you piece one of these kits together on your own, you will need intake manifold gaskets for Vortec cylinder heads and they can be obtained from either Edelbrock (#7235) or from GMPP (#89017465). It should also be noted that GMPP recommends GM intake manifold bolts (#12550027) for the Vortec-design cylinder heads-four-bolt attachment per side-because the bolt has a ball design on the end that seats in the head so it will not crush the intake manifold gasket. It should also be noted that you should tighten these bolts from the inside out, alternating sides and crisscrossing front to back. You will perform the torque sequence in two passes, with the first pass at 9 lb-ft and the second pass at 11 lb-ft. Please take note, it is 11 lb-ft and not a pound higher! These intake manifold gaskets are designed to seal at low clamp loads; excessive bolt torque may damage the gasket(s). You will also want to use an RTV sealant (3/16-inch bead) at the corners at the front and the rear of the block surface where the intake rests.
The steps to installing an intake and carburetor haven't changed much over the years. Having said that, you might want to pay close attention as we follow Jason Hooker of the Edelbrock engine department while he gives us a primer on how to install a dual-quad setup for your Vortec (or traditional) equipped small-block Chevy.