Carb Class: Fuel Bowl Basics
In past issues we have discussed that horsepower can be found in the individual components of carburetors - one often neglected component that is integral to the performance of your race car is the fuel bowl. While no one component is more important than another, the fuel bowl is integral to the performance of your engine and the way your race car goes down the track. All carburetors (no matter the size or brand) will have some type of system that controls fuel delivery to the carburetor. For the purposes of this article we will assume that most people use the same style of carburetor and have a removable "modular" style fuel bowl. Fuel bowls, for those that might not know, are the pieces of the carburetor that you would have to drain and remove to change the jets of your carburetor. If a fuel bowl is incorrect for the application or built with improper components the performance of your race car will ultimately suffer.
Fuel bowls come in different shapes, sizes, materials, and even colors. The choices a racer has when it comes to a carburetor can be overwhelming but with a little research and some good communication racers can ensure they will be satisfied with the combination and hopefully go some rounds. The first question you should consider when discussing fuel bowls is what type of fuel does your car use? E85, E98, race gas, and methanol all have a different BTU output and require varied amounts of flow to make best horsepower - ultimately you must determine if the fuel bowls can support the flow your engine requires. Another issue to be aware of is that certain fuels are corrosive, with that said, fuel bowls should be outfitted with components to resist any damage; if there is corrosion then one can assume there will be some particulate matter getting into the fuel system which will cause issues elsewhere in the carburetor. One of the last things we usually consider when outfitting a carburetor is the footprint of the carburetor (is there enough space between other components or another carburetor that you need to account for when choosing the size or type of fuel bowl?). With this information laid out one can now see that there is some considerable importance in the selection of a proper fuel bowl.
Modern race carburetor fuel bowls come in two basic configurations each with their own type of float. The first we will go over is the side hung bowl - named due to the nature of the way the float is situated inside the bowl itself. This type of fuel bowl is generally used in situations where a 2x4 set of carburetors must be mounted inline or on certain class carburetors where the rules require its use due to it being factory equipped. The side-hung bowl is compact, and because of that characteristic, has some limitations. One major drawback of side-hung bowls is that they do not offer much float drop - this compromises fuel flow by not allowing the needle to fully open. Another drawback to the use of the side-hung bowl is the float design itself. The float design of a side-hung float does not produce a high amount of leverage and therefore it cannot withstand much fuel pressure (the float has difficulty overcoming the fuel flow and shutting the needle). The other main configuration of fuel bowl is the center-hung style. Center-hung bowls are generally dual inlet (or dual feed) and unlike their side-hung brethren, you can opt to plumb them from either side. Named for the way the float is mounted within the bowl, a center-hung float offers more drop, flow, and leverage. A center-hung bowl is physically larger than a side-hung bowl and will have more capacity (something required on methanol and E85/98 race cars) which decreases the chance of running out of fuel and going lean down the track. Widely adapted and seen on the majority of carbureted race cars in the pits, the center-hung fuel bowl was the one of these two mentioned fuel bowls that was designed with performance in mind.
The last thing to consider when reviewing your fuel bowl setup are the specific components inside the fuel bowl. There are several brands and types out there for each little component so finding a quality piece is never an issue. Diaphragms, floats, and needle valves come in all shapes and sizes in a wide variety of materials to suit your application and should be selected with the help of a specialist. The right combination of components are what add up to a winning race car and your carburetor components play an integral part.