The Fuel Injection about Carburetor (1)
For the last few decades, fuel injection has morphed from a curiosity into an essential part of our daily transportation. Driven largely by the need to maximize fuel economy as well as the need to minimize emissions, EFI has also given us levels of reliability unfathomable with carbureted vehicles of yore.
Making the choice that’s right for your project.
For the last few decades, fuel injection has morphed from a curiosity into an essential part of our daily transportation. Driven largely by the need to maximize fuel economy as well as the need to minimize emissions, EFI has also given us levels of reliability unfathomable with carbureted vehicles of yore. On the hobby side of things, fuel injection has become increasingly popular as well. This has allowed us to pursue even greater levels of performance without the need for ultra-aggressive cam profiles and monster carburetors. It’s not surprising that more and more project builds center around electronically fuel-injected engines. But, in hot rod circles, the decision to choose EFI over traditional carburetors isn’t always so clear-cut.
In the last decade or so, we’ve seen a healthy growth in the traditional hot rod movement. This focuses on the back to basics approach, building cars that generally adopt the look and feel of rods built during the genre’s golden age, the late 1940s through the early 1960s. Although some cars adopt fairly radical profiles (extreme channeling and chopped tops), the emphasis here is using period parts or faithful reproductions to achieve the classic look. When it comes to engines and fuel systems, that pretty much means sticking with carburetors.
Besides tradition, another reason for sticking with carburetors is simplicity. Even the most basic of fuel injection systems are fairly complex, requiring specific intake manifolds, high pressure fuel lines, injectors and a high-volume pump to feed the system. With a carburetor, you don’t have these issues to contend with. Look at any small engine and, chances are, it will use a carburetor. From leaf blowers to lawn mowers to chain saws, carburetors are used because all they essentially need to do is provide enough air and fuel to start the engine, allow it idle and permit it to operate at wide open throttle. In automobiles, carbs are required to cope with more variables, such as change in engine speed, acceleration, and deceleration as well as extended idling, but the basic principles are the same.
In automobiles, different sized jets at different locations on the venturi are employed to handle different operating conditions. Most automotive carburetors also employ an emulsion tube, a length of pipe with small holes which is designed to pre-mix the air/fuel mixture before it enters the main venturi to achieve optimum combustion. By changing the size of these jets, specifically the main and air-bleed jets, along with the diameter of the emulsion tube and the number of holes, it is fairly straightforward to improve the engine’s performance. In order to reduce the risk of detonation but prevent flooding or fouling, many carb tuners aim for an optimal air/fuel ratio of 13:1. Airflow in carburetors is rated at CFM (cubic-feet per minute) – the greater the airflow, the more fuel required (via larger jet sizes).
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