Fuel Injection Vs Carburetor: The Biggest Pros And Cons

Anyone who has gone to school to learn how to repair engines of all types, such as myself, will have learned the fundamentals of how they work. It's crucial for troubleshooting and diagnosing engine failure. One of the most crucial fundamentals to understand is fuel delivery. With well over a century of development, many ideas have been introduced to make this process work, but, ultimately, most engines in existence use one of two options: a carburetor or fuel injection.

The basic function of both carburetors and fuel injection is to blend fuel with air in such a way that it can burn efficiently once introduced into the combustion chamber of an internal combustion engine — that includes all gasoline and diesel engines, plus a few others burning alternative fuels such as propane or natural gas. The primary goal of either system is to deliver air and fuel in a stoichiometric ratio, which is the optimum balance of fuel and air for complete combustion to occur. The secondary goal is to deliver the fuel as efficiently as possible. In modern times, a tertiary goal is to do all this with the fewest possible harmful emissions resulting from combustion. Fuel injection and carburetors go about fuel delivery using markedly different processes, and these are the biggest pros and cons of each system.

First built in 1906, the Antoinette 8V aviation engine was the first gasoline engine with a primitive forerunner of fuel injection. The technology was further refined but remained confined to aviation until the 1940s. Fuel injection systems first appeared on race cars in the '40s, but it would not be until the '50s that production automobiles received fuel injection, with the release of the Mercedes-Benz "Gullwing" 300SL.

Fuel injection systems rely on pressurized fuel delivered by a high-pressure pump in the fuel tank to valves called injectors on the engine. The fuel is delivered into the engine directly from the injector, which has several pinholes to atomize the fuel as it enters the airstream into the engine. A throttle plate controls airflow while sensor inputs control fuel flow and engine sensors control injector pulses' timing.

Early systems relied on various pumps, diaphragms, and other mechanical sensors to operate. They were complicated and expensive, and so used mostly in luxury and sports cars. Eventually, that was replaced by electronic fuel injection, which used multiple electronic sensors to monitor engine conditions to be calculated by an electronic control unit that would activate the injectors, and deliver the precise amount of fuel at the right time. 

Early throttle body systems had fuel injectors instead a carburetor but were replaced by more efficient port injection systems with individual injectors on the intake port of each cylinder, the most common system today. The newest system, which is growing in popularity, is called direct fuel injection, and its fuel injectors spray fuel directly inside the combustion chamber.

The evolution of fuel injection charted a course full of innovation and sophisticated solutions. Mercedes-Benz equipped its 1954 SL300 cars with a fuel injection system that its race cars had previously developed from the infamous Messerschmitt Bf 109 WWII fighter plane. A few years later, Chevrolet Corvettes were offered with a Rochester Ramjet mechanical fuel injection system. Although this option cost around $500 in the late '50s, it delivered a benchmark one horsepower per cubic inch and measured its fuel requirements from vacuum inputs, delivering fuel through a mechanical distributor and eight fuel lines.

In 1957, Chrysler offered the Bendix Electrojector system as an option on some models. This was the first electronic fuel injection system, although it was not digital. It used a controller made with analog circuitry and, in early iterations, vacuum tubes. All cars sold with this option were recalled, as the primitive electronics failed miserably in real-world conditions. VW improved on this with Bosch D-Jetronic fuel injection, which proved to be reliable, thanks to its solid-state circuitry. More refinement came to fuel injection systems as Cadillac introduced electronic fuel injection on the 1976 Seville. And in 1980, Bosh introduced Motronic, the first system controlled by integrated circuits.

For the last 40 years, fuel injection systems have become more advanced, precise, and efficient. With even higher-pressure secondary fuel pumps, direct injection sends highly atomized fuel directly into the cylinder with precision, to further increase efficiency and power output.

The primary reason for choosing fuel injection is clear: efficiency. A carburetor can not come close to metering the exact amount of fuel needed at exactly the right time in the way modern electronic fuel injection can. Mechanical fuel injection can also offer greater efficiency than a carburetor, but electronic systems are by far the most efficient.

The makeup of fuel injection systems at their core is relatively simple. They all use some kind of injector, a throttle, a fuel pump, and an array of sensors. However, the software and engineering of modern fuel injection systems are highly complex, contributing to the high cost of development. The components in the early days had to be designed and custom-built, but now the technology has been around long enough that individual parts are more affordable. Furthermore, with decades of production, fuel injection systems have proven to be incredibly robust and easy to diagnose with the right scan tool and a little bit of training.

For drivers, this all means you enjoy better fuel mileage, more power, and increased reliability. Electronic fuel injection requires no adjustments or tune-ups and eliminates all of the problems of cold starting and cold-weather performance.

[Featured image by OSX via Wikimedia Commons | Cropped and scaled | CC BY-SA 3.0]

For the vast majority of modern applications, fuel injection will provide more efficiency with reliable operation. It is more expensive to produce and install, but the technology has matured and proliferated enough to bring the prices down significantly from what it was during its infancy. In some limited applications, a carburetor may be the preferred choice, usually due to cost and simplicity. In remote regions with limited resources, where modern computers and testing equipment are unavailable, having a carburetor could be beneficial as repairs and adjustments can be done mostly with basic hand tools.

Fuel injection is the rational choice for all applications in which its cost does not climb to an untenable level. In small engine applications, the use of fuel injection is growing, particularly among equipment at the higher end and targeted toward professional use in particular. However, the small engine carburetor market remains huge, involving many global manufacturers who still see growth potential on the horizon. Nonetheless, battery power continues to grow in applications traditionally using small engines. Regulations coupled with consumer demand could see more small engines swapped for batteries in the years ahead.