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CCS’ Holley Carburetors

CCS’ Holley carburetors are used specifically by racers in all types racing. This article isn’t meant to be a do-it-yourself guide but rather a walkthrough of the changes needed to make 2 bbl carburetors competitive in oval track racing. Make no mistake: in oval track racing at any level, there are very few truly stock 2-barrel carburetors.
Because the Holley 4412 and 7448 are the most commonly used carburetors today, they are the main emphasis of this article. At three inches of vacuum, they are rated at 500 and 350 cfm, respectively. The 350 carb is more common in the South, whereas the 500 carb is more common in the North. The Rochester and Motorcraft carbs have the same issues, but they are handled differently.
Carburetors with two barrels have a vacuum rating of 3 (40.80)inches. Meanwhile, 4 bbl carbs measure 1.5 (20.40) inches. A 650 carb on a 358 cubic inch engine will seldom encounter 1.5 inches, but a 350 carb on the same engine can regularly see 5 to 8 inches. The 350 carb is really running around 430-440 cfm at 7 inches of vacuum.
The tendency of these carbs to run extremely rich at high rpm is their defining feature. Fuel pours from every hole of the carburetor at high rpm, whether it should or not. As a result, while jetting for high rpm, the idle and middle are extremely lean. As the vacuum builds at higher rpm, most carb builders adjust by shutting the power valve to lean out the mixture.
It's risky to do this with a standard carb since the power valve circuit flows a lot of fuel, and losing all of it when the valve closes would result in a lean state. Internal changes are used to lower the quantity of fuel delivered through the power valve so that there is still enough flow when it shuts to maintain the correct air to fuel ratio. The main circuit raises the flow rate.
The changes won’t end there. Because fuel runs through every orifice, all circuits must be altered to ensure correct fuel management at all rpms.
Because carburetor changes are engine specific, carbs from one engine may or may not work on another. The key distinction is that the port velocity and camshaft selection significantly impact the signal to the booster. The rod length, track size, and driver choice all play a role in cam selection. When a builder tries a new cam, they may pick it depending on the carb they were using at the time.
At maximum torque, the air-fuel ratio should be the highest. This is where the engine performs best. The car should be geared to exit the turn at a speed of 2-300 rpm above maximum torque, never below maximum torque. At maximum HP, the fuel mixture should be a little thinner. An excessively rich carb will have a smaller power band.

A Summary of Holley Carburetor Modifications

Each carburetor may be customized to meet the demands of individual customers. Here are some of the modifications we can make:
  • Plug all unnecessary vacuum ports, as well as the throttle shaft end hole.
  • Screw-in air bleeds are installed and sized in concealed or standard areas.
  • Channel restrictors for power valves are installed and sized (either press-in or screw-in).
  • Power valve channel restriction holes are sometimes moved by plugging existing ones and machining new ones. Where necessary, install PV blowout protection.
  • A custom-sized squirter or a larger pump system is installed, and the linkage geometry is enhanced. The right pump cam for the job is chosen.
  • Shafts are thinned, deburred, straightened, and, if legal, re-plated for corrosion resistance. Where permitted, special stainless screws are utilized.
  • The throttle bores on alcohol carbs are made larger by about 0.010" to minimize stuck butterflies.
  • Teflon or bronze bushings are used whenever shafts are re-bushed. Base plates are frequently extended, and bespoke butterflies are utilized when rules allow.
  • The taper angle in the venturi is altered, and the whole bore is polished. If regulations allow, the casting line is eliminated from standard diameter venturi as well as custom-sized ones.
  • Professional tooling is used to install boosters, which are then tightened, tested, and aligned to ensure an appropriate booster signal. Where rules allow, custom-sized and machined "stepped" boosters are frequently employed.
  • To rectify casting faults and attain gasket seal, all gasket surfaces are flat milled and then re-plated.
  • Idle feed restrictors are put in the main body or the metering block, depending on the demands. Where rules allow, the choke horn is machined off, the carb's entrance region is rounded and deburred, and a new vent tube is placed on regular body carbs. On HP bodies, all small casting imperfections are removed.
  • To prevent unfiltered air/dirt from entering, the choke rod hole is permanently closed and not shut with epoxy.
  • The main wells are enlarged to meet the requirements of the application. Emulsion channels are increased, and the emulsion bleed system is completely rebuilt. Up to 5-7 bleeds are placed. Removable and adjustable screw-in bleeds are frequently used.
  • Depending on the application, the appropriate jets, PV, and restrictors are placed. Instead of cork seals, stainless idle mixture screws are used with O-rings. Baffles for the vents are fitted.
  • Completely unique metering blocks are created from scratch in alcohol applications utilizing bare unfinished blank castings.
  • For corrosion protection, all machined surfaces are re-plated.
  • Where appropriate, oval track floats are added, or new brass floats are utilized in alky carbs. Large stainless steel alky needle/seat assemblies or high flow Viton-tipped needle/seat assemblies are employed.
  • Instead of paper, all screw washers are constructed of re-usable Nylon, which allows for limitless adjustments or removal and doesn’t leak.
  • Nylon is also used for fuel intake washers. Special pump diaphragms that tolerate methanol corrosion are employed in alcohol applications.
  • Dry float settings with a standard jig eliminate human error from "eyeballing."
  • Carbs are flowed on a flow bench after assembly with all top-quality gaskets, and the correct final tuning of the "real world" fuel curve is plotted out and double-checked. This mostly produces "advertised" cfm statistics; however, the figures for wet and dry flow are unrelated. Lower wet flow statistics may result from an increase in dry flow. Many carburetors are also tested in the engine test cell.
  • Finally, we'll look after your carburetor. To avoid damage to the throttle shaft and bushings, always use a positive throttle stop. For added safety, numerous throttle return springs should be utilized. To get the most out of them, make sure they're in line with the linkage at the right angle. Finally, remove the carburetor from the engine and dump all the fuel during long-term storage.
  • Via the vent tube, spray a generous amount of WD-40 or equivalent oil into the bowl and crank the throttle a few times to get it into the accelerator pump passageways. Spray the exterior of the carb and place it in a plastic bag. It's astonishing what can get inside a carburetor that has been left on the vehicle for an extended period.

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