Question: What is the difference between a fuel injected car and a carbureted car and which is better?

Answer: The carb and fuel injection do the same job on an engine. Both technologies introduce fuel particles to the air entering the engine intake to support the internal combustion which ultimately gives us power at the driving wheels. I think in a previous article we talked about a thing called an air fuel mixture where the engine needs about 14 pounds of air for every pound of fuel that it consumes, well the carb and the fuel injection supply the fuel part of the mixture by "atomizing " or breaking a fuel stream into a bunch of droplets and introducing the droplets into the air as it is ingested by the engine. 

The carburetor is a cast metal component that has a myriad of channels through it with "jets " or little controlled sized orifices at the entrances to the channels that allows the fuel to flow from an interim little internal storage reservoir There is at least one large hole in the middle someplace that the engine takes in all its air through this hole has some sort of flap or gate that allows the operator to control or throttle the amount of air that the engine gets and there fore control the engines operating speed. Just before this throttle plate there is a restricted area called a venturi that all the air that gets to the throttle plate has to go through to get into the engine . The operation principal is fairly simple the air entering the engine through the venturi has to speed up because the diameter is smaller than the tube before the venturi and after the venturi restriction - - the venturi (vena contracta) is shaped in such that the air speed increase makes a vacuum at a certain point along the restriction.  There is a small capillary hole in the vacuum area that is connected to the fuel reservoir and the vacuum sucks some fuel out of the reservoir and it mixes into the air that is blasting through the venturi on its way into the engine. The small capillary channel is plugged by a little screw in "jet" or orifice that has a appropriately sized hole in it that only allows a measured amount of fuel through the hole on its way to the venturi.

If you have heard of someone "jetting a carburetor " what they are doing is changing the fuel orifice size to get it just right for the amount of oxygen that is present in the air. There is a complication - -- the throttle is not always in the completely open position - - not even in racing - - so there are additional jets and correction jets in order to handle idle and mid range running conditions and a device called an accelerator pump that squirts extra fuel down the throat to get the engine to react when we want it to speed up. The other factor is cold start and running conditions -- when an engine is cold it doesn't run very efficiently because it is designed and all the parts are sized to run at an operating temperature -- so the mixture or air and fuel has to be substantially different (more fuel less air) and we have things like chokes that restrict the air volume until the engine gets warm on carbureted street cars and on race cars they just plain run rough until they warm up.

The start of fuel injection: 
The more modern street car carburetor is a mass of hoses and levers to try and meet the emission standards and driving conditions - - a simple device that has become over complicated but does work . In racing the carburetor was the state of the art at one time but it started to become the limiting factor in horsepower development. Most of the internal combustion engine technology in the 1930's and 1940's really came from the aircraft engines developed for the 2nd war and it was realized that better performance could be gained from more precise fuel delivery to the cylinders. The carbureted aircraft had some operating difficulties when the aircraft was in an inverted attitude as it relies on gravity to keep the fuel in it's storage bowl. On race cars when the cars went around corners there were only certain carb manufactures that more or less mastered nullifying the effects of cornering "G's". The merits of a system that would not be affected by gravity was therefore a big motivator in developing a different system for fuel delivery. So "fuel injection" made its debut on gasoline engines in aviation during the war and on some cars just after.

Fuel injection is simply a nozzle that sprays fuel into the airstream going into the engine - -it therefore does not have to rely on any natural phenomena like gravity or engine vacuum and in fact it goes one step better as it is unaffected by gravity . when introduced on aircraft it was an advantage as the engine kept running no matter what the aircraft's adopted attitude was in car racing no matter what kind of cornering forces were present the engine could now be immune. The early simple fuel injections were pretty straight forward (like the early carb). The early systems consisted of some sort of fuel pump to create pressure in the "hoses" that carried the fuel to the individual cylinders and some sort of nozzle on the end of the hose would spray the fuel into a mist. sort of like putting your thumb over the end of a garden hose to spray water on the lawn or to rinse your car during its weekly bath. even these early systems had the advantage of delivering more or less equal fuel to each cylinder over the carb and manifold system that had to hope that the airflow with the fuel droplets in it would treat each cylinder the same. Piston aircraft engines today that have fuel injection use still a derivative of these early simple systems because the simplicity means that there is less to go wrong. 

It was soon realized that if you could time or synchronize when the engine got the fuel delivered, a performance enhancement was possible so mechanically timed injection emerged on some race cars in the 1950's and by the 1970's most front line race cars had injection. Carburetors were mostly retained by amateur classes of racing where there was a mandate to restrict cost and performance. One big advantage to the injection was when the driver wanted engine response coming out of a corner for instance and he gave the engine more open throttle the engine response was immediate - - the engine would get the fuel for the amount of gas pedal whether it wanted it or not. These early mechanically injected cars were a lot of fun to drive.

With the advent of modern technologies that allow for very precise metering of fuel and very precise methods of measuring how much fuel the engine needs to run at peak performance and electronics that can react fast enough to control all of this, the fuel injection systems of today are far ahead of those of the past and fuel injection has emerged as the state of the art. We now spray the fuel through highly sophisticated electronic nozzles that are located in key positions along the intake of the engine to get optimum mixing of the fuel and air. We have things like manifold pressure sensors that tell the electronic brain exactly how much oxygen is in the air charge that the engine is ingesting so it knows how much fuel to give the engine, We have oxygen sensors in the exhaust system to verify the mixture for the computer etc etc.  The manufacturers would probably never meet any of the emission standards of today without the level of sophistication that is possible with today's fuel injection systems. 

Today fuel injection is definitely the superior way to deliver fuel to the cylinders and makes the kind of horse power development of the modern race car possible.