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1971 Chevy Corvette - Airspeed Indicators

Drag-Testing Induction Combinations On C3 Triple-Ex

Dave Young May 5, 2010
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With powerful engine choices, agile handling, and excellent stopping power, Corvettes of any vintage offer plenty to be happy with in terms of automotive performance. And while the Corvette is arguably one of the most enjoyable cars on the road to drive, some of us just can't leave well enough alone, and strive to optimize our vehicles through aftermarket modifications. One of the most common upgrades, and one we faced on Project C3 Triple-Ex, was choosing the proper induction system for our combination. Wanting to test different real-world combinations, we ordered several intake manifolds from Summit Racing Equipment, then drag-tested them to see which performed the best.

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There are many ways to choose an induction system for the engine in your Corvette. If you're building the engine yourself, you or your engine builder can decide which intake manifold and carburetor are the best match, considering your car's weight, chassis, engine displacement, operating-rpm range, and power level. If you're fortunate, you'll also be able to test and tune different combinations on an engine dyno, putting real numbers to the different intake and carb setups. Since the small-block in our '71 project car was already built when we got the car, an engine dyno wasn't an option, so we decided to test different induction systems in a fun way: at the dragstrip.

While the engine in your Vette is likely different from the 350 in our car, testing parts at the track can still be accomplished in the same manner. Just like dyno testing, however, consistency is the key. Weather and track conditions must be accounted for, and driving and staging techniques must be consistent for the data to be valid. With many years of drag-racing experience under our belt, we felt we were up to the task, so we evaluated our combination to decide which parts made the most sense for our car.

Though the previous owner of our Stingray did inform us that the engine was a fresh 0.030-inch-over 350 with about 9.5:1 compression, a fairly stout (nearly 0.500-inch lift) hydraulic cam, and roller rocker arms, that's about all we knew about the internals. On top of the motor were an Edelbrock Performer intake manifold and 650-cfm Edelbrock Performer carb, while a set of long-tube 15/8-inch headers and free-flowing dual exhaust handled the outflow of gas. While the engine ran well, with strong torque and power, it seemed to "lay over" above 4,500 rpm, which told us the small dual-plane intake and relatively small carb were likely restricting flow at higher rpm.

Not knowing our exact cam specs, we didn't know if our engine would like a higher-flowing dual-plane intake, or the additional plenum volume of a single-plane. In the end, we asked Summit Racing to supply an Edelbrock Performer RPM dual-plane and an Edelbrock Victor Jr. single-plane to test against the Performer intake that was on the car. C3 Triple-Ex was already equipped with a 650-cfm Edelbrock carb, and we chose a Holley 750 double-pumper along with a 1-inch carb spacer to test as well. We've found that these carburetors can make comparable power with proper tuning, but we chose the Holley for our article because it's arguably easier to tune at the track, and we already had a wide assortment of jets and tuning parts for Holley carbs.

With our parts on the way, we headed to the track for some baseline passes before making our changes. Unfortunately the fuel system couldn't keep up, and the float bowls ran dry at about 500 feet down-track, so we had to address that issue first. After installing a new fuel-delivery system from Summit, we were back at the track, where we recorded a best e.t. of 8.94 seconds at 79 mph (in the eighth-mile) with the Performer intake and 650-cfm carb. After establishing that baseline, we headed back to the shop to install the Victor Jr. intake and 750 carb.

As you'll notice, our testing was performed over a period of several weeks, during which time we had the car painted and installed different wheels and tires. While the paintjob likely won't affect our elapsed times much, we should note that the tests of the Performer RPM intake and 750 carb were performed with lighter SLP aluminum wheels and somewhat stickier Nitto Invo tires in place. Follow along as we test these different combinations and show you which one worked best on our C3.

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Lakeland Dragstrip
Lakeland, FL



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