Carburetor vs Port Injection vs Direct Injection (Explained)
Updated: Oct 16, 2021
In this article, I'll be comparing the various types of fuel injection technology, more specifically, carburetors vs port injection vs direct injection.
There are multiple types of carburetors and they're almost exclusively used on older vehicles, essentially every modern car uses a form of direct fuel injection.
With carburetors, the fuel gets drawn into the intake by the air flowing through it, whereas with a fuel injection system, the fuel pressure and injectors are finely-controlled by a complex set of sensors and computer systems.
Though fuel injection systems are much newer, they are undoubtedly superior to the carburetor, providing more power, greater fuel efficiency, and fewer pollutants.
Read on below to learn more about the specific advantages and drawbacks of each type of fuel system and whether to upgrade from a carburetor to a fuel injection system.
Table of Contents:
A carburetor, also known as a carburettor, is a device that combines air and fuel for internal combustion engines to achieve the proper air–fuel ratio for combustion.
The word is sometimes abbreviated as carb in various countries and regions.
Carburetors have largely been replaced by computer-controlled fuel injection systems in most vehicles, such as port and direct injection.
The carburetor operates on the Bernoulli principle, which states that the quicker air flows, the lower its static pressure and the greater the dynamic pressure.
The throttle does not regulate the flow of fuel directly. Instead, the quantity of fuel pulled into the airstream is determined by the speed of this air flow.
Benefits of the Carburetor
Though modern fuel injection systems are better and more advanced, there are some advantages to a carbureted fuel system, as listed below.
Usually, carburetors are much cheaper to install than a computer-controlled fuel injection system, normally they are a simple bolt on job.
They're also cheaper to set up due to the reduced cost of additional parts compared to a fuel injection system.
Easier to Setup
A carburetor doesn't require an ECU or any computer systems or sensors.
It simply bolts onto the intake of a vehicle. Due to not needing any sensors, computers or programming, it is quicker and easier to setup.
Can Be Tuned Easily
You can still tune and modify a carburetor, usually by installing larger jets and less restrictive intake piping, etc.
It doesn't require any specific computer programming or ECU mapping compared to a fuel injected vehicle, making it easier to tune.
Drawbacks of the Carburetor
The carburetor also has some major downsides compared with fuel injection, as listed below.
Cannot Keep a Consistent A/F Ratio
Carburetors have difficulty in keeping a consistent or perfect air/fuel ratio.
Maintaining a consistent and perfect air-to-fuel ratio is essential for making power and also for fuel efficiency, an improper ratio can result in power loss and reduced fuel economy.
Because a carburetor is based on air flow it is not 100% accurate, compared with a fuel injection system which uses accurate sensors and extremely fast computer systems.
Lots of Moving Parts
A carburetor has a lot of moving parts, making it unreliable and prone to failing.
Fuel injection systems have minimal moving parts in comparison, making it much more reliable than a carburetor.
Though, spare parts for a carburetor are usually inexpensive, negating this drawback somewhat.
Reduced Fuel Economy & Power Potential
Due to a carburetors reduced air/fuel ratio consistency and accuracy, it can result in an improper ratio of air and fuel, reducing fuel efficiency and power.
Also, there is no adjustability to the air/fuel ratio, making systems like anti-lag, pop and bang maps, etc very difficult or impossible to do without fuel injection systems.
What Is Direct & Port Injection?
Direct injection is a method for forming mixtures in internal combustion engines that operate on gasoline (petrol), in which fuel is delivered directly into the combustion chamber.
Manifold fuel injection systems, on the other hand, inject fuel into the intake manifold, this is also commonly known as port injection.
Direct injection may assist improve engine efficiency and specific power production while also lowering exhaust pollutants.
The first direct injection engine went into production in 1925 for a low-compression truck engine.
Port injection has its own specific advantages and drawbacks when compared to direct injection.
Port Fuel Injection
With port fuel injection, fuel is injected into the intake manifold, where it mixes with air before being drawn into the cylinders.
Whereas direct injection injects fuel directly into the combustion chamber.
Sometimes, direct injection and port injection are combined and sometimes there can be multiple port fuel injectors, such as 1 injector, 1 per cylinder, 2 per cylinder, etc.
Their effectiveness and reduced maintenance meant port fuel-injection systems were the first to replace carburetors; nowadays, direct injection has largely replaced port injection.
Although port fuel injection systems are more efficient than carburetor systems, direct injection is even more efficient.
Advantages of Port Injection
Port fuel injection systems have some specific advantages when compared to direct injection and carburetors, as listed below.
Another advantage of port injection systems is they are cheaper to install than a direct injection system.
Better Fuel Mixing
The advantage of port injection is that it enables air to mix more evenly with the fuel being injected before being entering the combustion chamber.
When using direct injection, the fuel has less time to mix with the air entering the cylinder, which may result in hot spots forming within the engine cylinder.
Hot spots within the cylinder can be detrimental to the engines lifespan and can also increase the chance of knock.
Has a Cleaning Effect
Port injection can also have a cleaning effect on the intake valves and intake port, the cleaning of the intake valves and ports can help improve efficiency and power.
This is an advantage specific to port injection and is one of the reasons why some manufacturers decided to incorporate both direct and port injection into some vehicles.
More Efficient Than Carburetors
Port injection is more efficient than a carburetor but less so than direct injection.
Carburetors are reliant on air flow and are not completely accurate, port injection is determined by the ECU and is much more accurate, providing better efficiency.
Can Be Added Aftermarket
Unlike direct injection which requires a port to be in cylinder head for the injector, port injection can be added as an aftermarket part on essentially every vehicle.
It can be incorporated into the intake manifold, throttle body, intake piping, etc.
Drawbacks of Port Injection
There are many advantages to port injection over carburetor systems, but there are also some disadvantages of port injection systems, especially compared to direct injection.
Less Efficient Than Direct Injection
Gains in efficiency when switching from port injection to direct injection can be up to 15%.
Direct injection is much more efficient than port injection systems. It's likely due to direct injections ability to atomise the fuel better, resulting in a more complete combustion.
Atomises Less Than Direct Injection
Port injection doesn't atomise as well as direct injection does. Atomisation is the process of splitting larger fuel droplets into a very fine mist.
This enhanced from direct injection atomisation provides a much more complete combustion process when compared to the fuel droplets found with port injection.
Although port fuel injection mixes the air and fuel well, the droplets are larger, resulting in a less complete combustion and not as efficient.
Direct injection engines generate the air and fuel mixture directly in the combustion chamber.
Through the open intake valve, only fresh air enters the intake port. High-pressure fuel injectors deliver the fuel directly into the combustion chamber.
This is unlike carburetors and port injection systems, in which both have fuel travelling through the intake piping.
Advantages of Direct Injection
There are a couple advantages of using direct injection compared to port injection, such as those listed below.
Better Fuel Efficiency
Because the fuel is atomised instantly, it causes a more complete combustion, resulting in more power generated with the same amount of fuel injected.
It's not uncommon to see improvements in fuel efficiency of 15% just by switching from a port injection system to direct injection fuel system, this efficiency improvement is even greater when switching from a carburetor fuel system.
As mentioned above, the fuel injected from a direct injection system is almost instantly atomised, resulting in a more complete combustion event.
This also has a cooling effect on the piston at high rpms, though at low rpms the port injection system seems to be more effective.
Drawbacks of Direct Injection
Although direct injection has its benefits, there are also some disadvantages associated with its usage, as follows.
Direct injection systems require more components and more expensive components, such as a high pressure fuel rail, very strong injector tips, etc.
These expensive parts add up in cost, resulting in a much higher cost fuel system, especially when compare with port injection and carburetors.
More Difficult to Control Emissions
Because the fuel is sprayed directly into the combustion chambers, it may not mix as well as port injection does, resulting in air escaping the combustion chamber.
Although a more complete combustion event occurs, the air that escapes can increase the emissions of a vehicle.
Some advancements have been made in this regard, such as various piston crown designs, turbocharging, multiple-hole injectors and injector pulsing, all of which can improve the mixture of air and fuel, helping to reduce harmful emissions and further improve efficiency.
Which is Better?
Simply put, direct injection is the single best type of fuel injection system. It has enhanced efficiency and performance when compared to port injection and carburetor systems.
That said, the combination of port injection and direct injection can be a very powerful and very efficient method of fuel injection.
Port injection has the unique advantages of cleaning the intake valves and port, as well providing low-speed efficiency boosts, it also mixes the air and fuel very well.
Whereas direct injection atomises instantly, providing a very complete combustion, leaving minimal fuel unburnt, providing very high efficiency.
Combining the two can create an almost fully complete combustion, leaving no air or fuel left in the combustion chamber, providing the highest efficiency and lowest emissions.
It is also excellent for usage in high-performance and tuner cars, as this combination has a cooling effect on the cylinder and piston, reducing the chance of engine knock.
Though this type of fuel system can become very expensive and complicate to set up.
Overall, the combination of port and direct injection is best, but direct injection is best if just one type of fuel injection system is being used.
Should You Upgrade to Fuel Injection?
If you have a carburetor, should you upgrade to port injection or direct injection? Maybe, it could increase performance, efficiency and reliability significantly.
What about if you have port injection, is it worth upgrading to direct injection or adding it to your current port injection system? It's probably not worth it, you would have to reprogram the ECU, spend a lot of money on a new or custom cylinder head, and a lot more.
But is it worth adding port injection to a direct injection vehicle? Possibly, but probably not. It would require a custom manifold with ports for the injectors, a new fuel pump, a repogrommed ECU, etc.
It would be expensive for little gains, unless you want a highly-tuned, extremely-efficient or a racing car, it is likely not worth upgrading, unless you have a carburetor system.