Carburetor vs Fuel Injection: Understanding the Pros and Cons

Which offers the best performance, carburetor vs fuel injection, is highly debated question among car enthusiasts. Many believe that performance is best with a carburetor while others insist that the only way to go is with fuel injected gasoline. To determine which is best for your vehicle, it is important to understand how both components work.

To start any conversation on carburetor vs fuel injection, one has to think back to the very beginning of the internal combustion engine. Since the dawn of the internal combustion engine, we have needed a way to get air and fuel into the cylinder, where it could be ignited and thus give us usable mechanical energy. Some of the first engines relied on a simple fuel drip, but better ways of introducing fuel into the cylinder would eventually come along.

HISTORICAL PERSPECTIVE

Early carburetors relied on air flowing over liquid fuel or a wick, gathering fuel vapors for ignition. Later versions would utilize the Bernoulli principle to better meter the amount of fuel going into the cylinders, that is, the air flowing through a venturi would deliver fuel in proportion to the amount of air going into the intake. By the time the last carbureted vehicles in the US died out, in the early 1990s, fuel injection was already in full force.

Fuel injection as we know it actually has its roots as far back as the first engines, back in the 1880s; however, its complexity prevented it from being utilized on any scale until the 1920s, and it was still limited to compression-ignition diesel engines. Later, in the mid-1950s fuel injection systems would appear on both diesel and gasoline engines, in both mechanical and electronic versions.

The first electronic fuel injection systems, using a throttle-body injector, simply replaced the carburetor. Port fuel injection placed individual fuel injectors closer to each intake valve, which powers most modern automobiles. Later, like diesel engines, some gasoline engines would be fitted with direct fuel injection, which puts fuel directly into the cylinder. Some direct fuel injection systems co-exist with port fuel injection systems.

Engine Performance

The carburetor vs fuel injection performance is mainly due to the amount of air and gasoline that can enter the engine cylinders. The cylinders contain the pistons and combustion chambers where energy is released from the combustion of gasoline. The carburetor and fuel injection system will both feed fuel and air into the engine.

The Carburetor

The carburetor contains jets that will push the gas into the combustion chambers. The amount of fuel that can flow through these jets depends completely on the amount of air that can be pulled into the carburetor venture. The main issue with obtaining the best performance using a carburetor is that it cannot monitor the air to fuel ratio for each individual cylinder. If there was a carburetor for each cylinder, then this would not be an issue. So, with a carburetor, the best fuel to air ratio for each cylinder is approximated for the best performance. However, carburetors do last longer than fuel injection systems and are favored in motor sports. Carburetors are also much simpler to install than fuel injection systems because there are no electrical components or return lines to the fuel tank. The carburetor is currently much less expensive than the electronic fuel injection systems.

Carburetors meter fuel into the engine by using a physic phenomenon called the Vacuum Venturi Effect. When you give the vehicle more throttle, more air is forced through the venturi tube (a tube design that become narrow, increasing the speed of the air flowing through it) in the carburetor.  This draws additional fuel into the engine.

As a vehicle ages it may develop vacuum air leaks from the many vacuum lines used in the engine compartment. These leaks cause additional air to be drawn into the intake manifold, changing the fuel/air mixture from the right blend of fuel and air to more of a lean mixture – too much air, not enough fuel.  Any time you add additional air to the intake system with the same amount of fuel as before, it results in an extremely high combustion chamber temperature – a temperature increase, if you will.

Now, for several years before the industry went predominantly to fuel injection, they did have what is called “feedback carburetors” which were computer controlled. These carburetors had the same ability to control the air/fuel ratio but were not as efficient as fuel injection. But carburetors traditionally have had the issues listed above.

 Fuel Injection Systems

Fuel injection systems are becoming more popular for those wanting the best performance from their engines. There are two different versions of fuel injection – port fuel injection and direct injection. Port fuel injection is the most used and direct fuel injection is the latest developed fuel injection system. This system was designed specifically for four or two stoke engines. The main benefits to using direct injection is that the amount of fuel and air can be perfectly released and then injected into the cylinder according to the engine load conditions. The electronics used in the system will calculate this information and constantly adjust. This type of controlled fuel injection results in a higher power output, greater fuel efficiency and much lower emissions. One of the main issues is that these systems are sophisticated and will cost much more than a carburetor. Installation is more complicated as it uses an electrical component and custom cylinder head configuration.

Computer-controlled, electronic fuel injection systems consist of a computer, an oxygen sensor, a set of fuel injectors, a fuel pressure regulator, and an electric fuel pump. The oxygen sensor reads the air/fuel mixture in the exhaust and produces a voltage reading. Keep in mind that a rich air/fuel mixture (too much fuel, not enough air) has a lower combustion temperature and a lean air/fuel mixture (not enough fuel, too much air) has a hotter combustion temperature.  The oxygen sensor can generate voltage from 0 to 1,000 millivolts.  Anything over 500 millivolts is a rich mixture and anything below 500 millivolts is a lean mixture, whereas 500 milli bolts is “just right”. The computer’s mission is to keep the voltage around 500 millivolts – the reading you get when the air/fuel mixture is equal to the idea mix of a 14.7 to 1 air/fuel ratio. This is called the stoichiometric ratio and is what the catalytic converter needs to perform its job at peak efficiency.

What does the computer do to keep the ratios at their best? The computer does this by extending or shortening the length of time fuel injectors are held open. If the computer sees voltage below 500 millivolts (remember, lean mixture) it will hold the injector open longer to richen the air/fuel mixture to get back to the 500-millivolt reading. If the computer sees a voltage reading above the 500 millivolts (remember, rich mixture) it will shorten the time injectors are held open to again get back to the 500 millivolts. 

The questions that were presented at the beginning of this article can be explained now that we know this information. Carburetors have no mechanical ability to correct lean or rich fuel mixtures. If air leaks develop in vacuum lines, there will be excessive heat in the combustion chamber (too much air makes it hotter). This excessive heat can damage or melt spark plug electrodes, burn valves, and take the tension out of piston rings, resulting in excess oil consumption and a shorter engine life. If a rich mixture is present, possibly due to carburetor float problems or a sticking choke, you will get poor fuel mileage, bad emissions, and carbon build up on spark plugs and pistons. This will shorten spark plug life and raise the compression, causing the engine to require higher octane fuel to prevent pre-ignition problems.

Modern engines last longer because they have electronic fuel injection that simply corrects the air/fuel ratio, so you never have an excessively rich or lean condition. This is the main reason spark plugs last longer, valves are not burned, and piston rings do not lose their tension resulting in shorter engine life. If the problem is too great for the computer to correct, it will turn on the check engine light located on the dash which is your clue to take the vehicle to a mechanic to correct the problem.

Which Is Best?

It is obvious that most automobiles will be changing to fuel injection systems due to the lower emissions. However, unless the cost of these systems decreases significantly then there will still be a massive following that will stick to carburetors. When looking at pure horsepower, the fuel injection system only delivers about 10 extra horsepower at peak. It is the ability to constantly be tuning the fuel and air intake for each cylinder that benefits the performance. The fuel injection systems are the best as they will decrease vibration and help to overcome steep grades that are traditional terrain for off-roading. Again, which one is best completely depends on where and how you are driving.

CARBURETOR VS FUEL INJECTION: PROS AND CONS

  • Emissions and fuel economy. Fuel injection, because it can be more precisely controlled, results in more efficient use of fuel, reduced fuel consumption and fewer emissions, which is the main reason it began to replace the carburetor in the 1970s.
  • Power and performance. Again, because fuel injection and modern electronic controls are more accurate, fuel delivery can be tuned to match driver demand. Carburetors are precise, but not accurate, in that they cannot account for changes in air or fuel temperature or atmospheric pressure.
  • Cost and complexity. Being purely mechanical devices, carburetors have it hands down over fuel injection regarding cost and complexity. With a can of carburetor cleaner, simple hand tools and maybe a couple of spare parts, you can rebuild a carburetor on your porch or at a rest stop. Whereas with fuel injection, even with years of training and experience and a few thousand dollars in diagnostics gear, you will still need a tow truck to get you off the road should your system burn out on you. Most small engines, such as those on motorcycles, lawn mowers and snow-blowers, are still equipped with carburetors, simply because they are not emissions-regulated, inexpensive, simple, and reliable.

While the carburetor may have been around for over a century, fuel injection is a clearly superior alternative, delivering better power, fuel economy and lower emissions. For the modern driver, this is all you could ask for.

There are plenty of options out there for both carburetors and fuel injection systems, so you do have choices with fuel injection systems usually costing much more than a comparable carburetor system.

So do your homework and understand what you are getting for your money when making you decision on carburetor vs fuel injection.

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