With any car we build, restore, or modify, there are certain temptations we must avoid to ensure that the end product conforms to the performance and aesthetic standards we set at the beginning of the project. So while it may be tempting to install a high-powered engine in our '71 C3 at the outset, the fact is that the car itself won't be ready for a big-inch powerplant until we perform some basic upgrades. Adding incredible power to an otherwise factory Stingray is usually a recipe for disaster-since the engine will outperform the other parts of the automobile-so, as you've likely noticed, we're improving various portions of our car's systems to ready them for an upgraded powerplant. Last month we installed an aluminum radiator and other cooling system components to ensure our C3 doesn't run too warm, and this month we'll be upgrading the fuel system with some high-performance components from Summit Racing Equipment.
In stock form, a properly maintained C3 fuel system is generally adequate if your engine isn't making more than 300 horsepower or so. Start adding components like a longer-duration camshaft, an aluminum intake, headers, and a big carburetor, however, and the system's shortcomings quickly become apparent. Although the previous owner of our project car had replaced the fuel tank and sending unit, and added an electric fuel pump, there were other issues with the car's fuel system that needed to be addressed before we could rely on our Stingray to perform like it should. A couple of issues ago, as we readied our car for the road, we fixed a couple of fuel-related problems and replaced some leaking lines. This month we'll go through the car's entire fuel system, greatly increasing its capacity to deliver fuel while making it more reliable as well.
Since our engine didn't have...
Since our engine didn't have a mechanical pump, we ordered this Holley high-volume unit from Summit. This pump provides 110 gallons per hour at a pressure of 6.5 to 8 psi and doesn't require an external regulator.
Carbureted C3 Corvettes like ours came with an engine-driven fuel pump that draws gasoline through a line to the pump and then provides pressurized fuel to the carburetor. The main problem with this style of system is the difficulty it has sucking gasoline the six or so feet from the fuel tank to the pump. If the pump can't pull enough fuel, it can't provide a pressurized fuel supply to the carburetor. Once the carb's float bowls run dry, the engine will run lean, and eventually stop running altogether. Though commonly called "vapor lock," the real name for this problem is fuel starvation, and it can have many causes, including clogged fuel filters or lines, corroded pick-up units, trash in the tank, or inadequate supply-line diameter.
Of course, the most common cause of fuel starvation is a fuel pump that's not rated to provide as much gasoline as the engine is using. This is generally what happens when you add a more powerful engine to a car without upgrading the stock pump. The car will run fine during normal driving, but once the throttle is opened, the pump simply won't be able to keep up with the engine's fueling demands. You can get away with this for a while if you don't drive too aggressively, as the carburetor's float bowls provide a buffer for the fuel system. As you apply full throttle, the bowls will drain, and assuming you let off the gas before they drain completely, they'll refill while the car is idling or cruising normally. Since Corvettes were made for aggressive driving, however, it pays to upgrade the fuel-delivery system, especially if you plan to increase the engine's output like we do.
During the initial inspection...
During the initial inspection of our Stingray, we noticed that the fuel tank and sending unit had been replaced with new parts. Working our way forward, however, revealed the inadequacies of the car's existing fuel system.
A previous owner had installed...
A previous owner had installed an electric fuel pump in the car and removed the stock mechanical unit. Although this aftermarket pump did allow the car to run and drive, it couldn't keep up with the needs of our mild 350 during full-throttle acceleration.