Just like racing around a circle track requires much more skill than the average fan can appreciate, properly fueling a circle track engine requires a far more specialized carburetor than the average racer may realize. Putting the power down efficiently when exiting a corner involves perfectly balancing the on-again-off-again relationship between the driver’s right foot and the gas pedal. Likewise, running in high gear lap after lap forces circle track engines to operate over a much broader rpm range than a drag car or road race machine, placing a premium on consistent fuel delivery at wide-open throttle. Consequently, meeting the performance demands specific to the circle track environment racing requires building a carburetor designed specifically for circle track racing from the ground up.
While modifying a street carburetor for race duty can work reasonably well, Quick Fuel Technology’s Q-Series circle track carbs offer substantial advantages in adjustability, consistency, and predictability. Since maximizing corner exit speed also increases straightaway speed, the driver that can hit the throttle the soonest can rocket past the competition. However, most circle track classes attempt to level the playing field by limiting tire size, which places the burden of putting the power down directly in the hands, or feet, of the driver.
In a standard street carburetor, the secondaries open up at a 1:1 rate. In other words, if the primaries open 50 percent, the secondaries open 50 percent as well. Depending on track conditions and chassis setup, an aggressive 1:1 opening rate can often lead to tires spin despite a driver’s best efforts to gradually roll into the throttle. To help remedy this problem, all Q-Series carburetors feature an adjustable QuickLink system. By simply swapping out the secondary links, the opening rate of the secondaries can be adjusted to 40-, 60-, or 100 percent of the primaries.
Very Different Fuel Curve RequirementsWhile providing a sufficient quantity of fuel is important in any race engine, delivering that fuel in a consistent and burnable fashion is equally as important. This is particularly difficult in a circle track engine that experience large changes in engine load and rpm lap after lap. Once a circle track car gets up to speed, it remains in high gear. As such, the difference in engine rpm at the end of the straightaways compared to engine rpm at corner exit can vary as much as 3,000- to 4,000 rpm. Since street carbs are designed to provide a margin of safety at high rpm by richening up the air/fuel mixture, they struggle to maintain a consistent fuel curve in these rigorous conditions. This can lead to lean or rich spikes in this critical 3,000- to 4,000 rpm operating window, which can then result in a lean hesitation or over-rich power loss.
In order to maintain a consistent fuel curve throughout the entire rpm range, QFT has optimized the cross-section of the fuel passages in the Q-Series carburetors. To assist in flattening out the fuel curve even more precisely, Q-Series carbs utilize metering blocks with five emulsion bleeds. Many street carbs only have three. Furthermore, screw-in air bleeds enable fine-tuning of both the low- and high-speed systems, while a proprietary booster design enhances carb signal without restricting high-rpm airflow. Since no two engines, tracks or cars are the same, this infinite level of adjustability allows dialing in a flat, consistent fuel curve throughout the rpm range in any racing environment.
Of course, precise metering isn’t possible unless there’s a steady supply of fuel flowing to the metering blocks in the first place. Simple physics dictates that racing around a banked oval pushes fuel to the passenger side of the car. To counter this, Q-Series circle track carburetors feature die-cast aluminum fuel bowls with internal baffles that eliminate slosh. The bowls also feature an integrated fuel chute that substantially reduces aeration, and directs fuel toward the main jet pickup area.
Precise fuel delivery aside, the Q-Series circle track carburetors boast a long list of features that distinguish them from a standard street carb. A vacuum-drawn, die-cast aluminum main body enhances strength and allows holding critical casting dimensions to much tighter tolerances. This simply isn’t possible with standard sand-cast bodies. Likewise, billet metering blocks eliminate porosity and internal leaks. CNC-machined throttle-body utilizes strengthening ribs for enhanced durability, thicker mating surfaces for improved sealing, and integral throttle-stops to prevent shaft over-centering at wide-open throttle. QFT’s circle track Q-Series are also equipped with sealed roller bearings on the throttle shafts for precise throttle “feel” and extreme durability, even on gritty dirt tracks.
Quick Fuel Technology’s Q-Series circle track carburetors are available in 750-, 850-, 950-, and 1,050 cfm configurations for both gasoline and alcohol applications. They not only take all the guesswork out of attempting to modify a street carb for circle track duty, they offer far superior performance as well.