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| Holley #4777 650 |
This carburetor was developed specifically for the DIRT Sportsman Modified series. While this carburetor is not as restrictive as many of the other “straight leg” booster carburetors, it is power limiting. When the rules were written, the intent of the restrictive carburetor was (1) to slow the cars down and (2) to equalize the performance of the engines. They did accomplish slowing the cars down but VDL Fuel Systems has done a superior job of keeping the performance unequal!
Whenever a carburetor is improperly sized to the engine there are a variety of problems that arise. The air/fuel circuitry was not designed for the air speed and booster signal of this application. What results is a fuel curve that is too lean on the bottom and too rich on the top. This is exactly the opposite from what the fuel curve should look like. VDL Fuel Systems has done extensive dyno and track testing to recalibrate the air/fuel circuitry, accelerator pump circuit, and idle circuit, producing optimum torque, horsepower, and drivability. |
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Airflow is of the essence with this carburetor. VDL Fuel Systems takes each part of this carburetor and maximizes the potential airflow while still operating within the tech parameters. VDL Fuel Systems has purchased tech tools so as to be able to take each dimension to the limit. From booster dimensions, booster location, and venturi diameter to the throttle shaft width, this carburetor must be custom fit to the tech tools. The performance gains from these modifications are significant and not something you can afford to leave on the table.
After the parts are machined to the minimum/maximum sizing, they are vibratory polished and recoated. Assembly is done to tolerances unobtainable in high volume production. Boosters are installed to within .001’’ on height, twist, and pitch. The base plate is matched to the main body. All gaskets are properly matched to the main body to prevent overhang. And finally, the throttle plates are adjusted for optimum position angle on the flow bench. VDL Fuel Systems produces the absolute best custom-built 650 CFM carburetor available. Think “outside the box” and put yourself out front with a VDL Fuel Systems carburetor. |
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| Application |
Description |
| DIRT Sportsman |
Venturis blueprinted to maximum sizing
Air/fuel circuitry recalibrated
Idle circuit calibrated
Accelerator pump circuit tailored to application
Welded throttle shaft
Base plate matched to main body
Boosters calibrated, sized, and precision installed
All parts vibratory polished for enhanced airflow |
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