This month we're drag-testing...
This month we're drag-testing three different intake manifolds, all in an attempt to make our C3 project car quicker and faster at the track. Is one of these intakes right for your Corvette?
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.
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.
We didn't think the Performer...
We didn't think the Performer intake and 650 carb on C3 Triple-Ex's 350 provided enough induction, and ordering some new parts from Summit Racing Equipment proved us right. We tested several combinations and found big gains by swapping the intake and carb.
Our preliminary trip to the...
Our preliminary trip to the track verified that our fuel system was woefully inadequate, so we installed a new Holley electric fuel pump and 3/8 fuel line from Summit.
Adding a 1-inch carb spacer...
Adding a 1-inch carb spacer helped the car a little, but the Performer intake and 750 carb didn't seem to be the best combination.
Back at the track with the...
Back at the track with the Edelbrock Performer intake and 650 carb, we tuned our combination and practiced launch technique until scoring a best eighth-mile pass of 8.94 seconds at 79 mph. When drag-testing, elapsed time is a good indicator of how the car is working, but mph indicates the horsepower of the engine. We hoped to improve both.
Feeling that our engine needed...
Feeling that our engine needed more induction volume, we switched to a 750 Holley carb. Our trap speed went up slightly, but elapsed time was down, indicating the small runners of the Performer intake weren't up to the task of delivering enough mixture.
Back at the shop, we drained...
Back at the shop, we drained the coolant and swapped on the Edelbrock Victor Jr. intake manifold. This intake is a single-plane design known for making top-end power. We knew we'd sacrifice some torque with this intake, but with a manual transmission we felt it should still run better than the Performer on our combination.
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.
The Victor Jr. intake has...
The Victor Jr. intake has an open plenum and fairly large runner volume for our warmed-over 350. We did see a big improvement in mph, and ran a quicker e.t. than we had with the Performer intake, but driveability suffered on the bottom end, making the car tricky to launch.
Launching C3 Triple-Ex with...
Launching C3 Triple-Ex with this combination was tricky, as we had to walk the fine line between bogging the motor and spinning the tires. Our best pass with the Victor Jr., the 750-cfm carb, and the 1-inch spacer was respectable-8.82 at 83 mph-but we lost some torque to gain that extra top-end horsepower.
We speculated that the Edelbrock...
We speculated that the Edelbrock Performer RPM intake would be our best option, but the vacuum fitting wasn't located correctly for our application. We drilled and tapped it for a vacuum fitting that would better accommodate our needs, then plugged the original port with a pipe plug.
Any debris or left-over gasket...
Any debris or left-over gasket material between the intake manifold and the heads can cause a coolant or vacuum leak. Always clean these areas and use new gaskets when replacing the intake.
The Edelbrock Performer RPM...
The Edelbrock Performer RPM intake is a dual-plane design, with less runner volume than the Victor Jr. single-plane but more volume than the standard Performer intake. Though dual-plane intakes are generally good for torque, the Performer RPM is also designed to flow well at high rpm, making it a good all-around choice for our 350.
Driving to the track, we could...
Driving to the track, we could tell the 350 had better throttle response and seemed to make more power. Our first pass proved it, as we ran an 8.80 at nearly 85 mph in the eighth.