Technical Articles
Individual Throttle Bodies FAQ
Q: What are individual throttle bodies (ITBs)?
A: Individual throttle bodies (ITBs) are a type of intake system used in internal combustion engines. Instead of a single throttle body, ITBs feature individual throttle valves for each cylinder. This setup allows for better airflow control and improved engine response.
Q: What are the benefits of using individual throttle bodies?
A: Individual throttle bodies offer several advantages. They enhance throttle response, increase engine power, and improve engine efficiency. ITBs also provide better cylinder-to-cylinder airflow balance and can enable higher RPM capabilities. Additionally, they can enhance the engine’s intake sound, giving it a more aggressive tone.
Q: Are individual throttle bodies suitable for all engines?
A: Individual throttle bodies can be used on various types of engines, including both naturally aspirated (N/A) and forced induction (turbocharged or supercharged) setups. However, the feasibility of ITBs depends on factors such as engine configuration, space constraints.
Q: Do individual throttle bodies require any modifications to the engine?
A: Installing individual throttle bodies usually requires modifications to the intake manifold and fuel delivery system. The intake manifold needs to be replaced or modified to accommodate the separate throttle bodies, and the fuel injectors may need to be relocated or upgraded. Additionally, the engine control unit (ECU) may need to be reprogrammed or replaced to properly manage the ITBs.
Q: Can I install individual throttle bodies myself, or should I seek professional help?
A: Installing individual throttle bodies can be a complex task that requires a good understanding of engine systems and tuning. If you have the necessary knowledge, experience, and tools, it is possible to install ITBs yourself. However, it is generally recommended to seek professional help from a qualified mechanic or engine tuner to ensure proper installation, calibration, and optimization for optimal performance and reliability.
Q: What engine control unit (ECU) do I need for throttle bodies?
A: Our throttle bodies will work with all aftermarket ECU’s, we would suggest discussing ECU options with your selection mapping provider as most tuners have a preferred brand which they are most confident with mapping. Some factory ECU’s can be re-mapped to run ITB’s, however re-mapping of the factory ECU requires special software so speak to an ECU specialist to find out if your ECU is mappable.
In this article, we will explain the benefits and limitations of the different types of inlet systems.
Single Throttle Bodies
A single throttle body is the most common setup found on production engines. The whole engine is feed air through the one throttle body mounted to an air chamber or plenum at is common to all the engine cylinders. Each cylinder draws air from the plenum during its induction cycle. This system is simple and reliable as there is only one moving part. An Idle valve or bypass valve can be used to allow a small amount of air to bypass the throttle body and feed air into the plenum so that engine will continue to run when the throttle plate is closed.
Individual throttle bodies
The use of individual throttle bodies is commonly found on motorsport engines and high-performance road vehicles. Adding throttle bodies is a popular modification for performance car enthusiasts on their road cars due to its improvements in engine performance & throttle response.
Unlike a single throttle body arrangement an individual throttle body setup has a throttle body for each cylinder of the engine, therefore a 6 cylinder engine would have 6 throttles.
The advantages of having a throttle body per cylinder are that it improves throttle response and allows for a larger inlet diameter. The improvement in throttle response is achieved by the shorter distance and reduced volume between the throttle plate and inlet valve, meaning less air is required to fill the space and get to the cylinder.
The increase in inlet diameter allows more air to flow into the cylinder. The size of inlet diameter does have an effect on the performance as explained in this article throttle bore and length
Direct to Head Individual throttle bodies
Originally many throttle body installations were based on DCOE carburetors arrangements but instead of using a pair of carburetors, a pair of throttle bodies would be used which have a fuel injector as the method of delivering fuel. This method worked well and allowed the fueling to be mapped to provide the ideal amount of fuel over the whole rev range.
Direct to head throttle bodies are individual throttle bodies that have been designed for a particular engine. This method of installation removes the need for an intermediate manifold and therefore allows the throttle plates to be moved closer to the head to further increase the throttle response as well as allowing the larger diameter inlet tract to be closer to the head reducing frictional loses and therefore providing more potential for power improvements.
True direct to head throttle setups have a detachable mounting plate that allows the head flange to be mounted to the head without the throttle bodies attached so that it can be ported to perfectly match the cylinder head inlet ports.
Normally aspirated
Individual throttle bodies are a common upgrade on normally aspirated engines as they increase the amount of air to the engine, which in turn allows more fuel to be injected and therefore more power. With a normally aspirated system, there does not need to be any plenum chamber or other restriction.
In some applications due to the location of the engine or noise limits, a plenum chamber can be used to feed cooler air to the throttle bodies and stifle the noise. The plenum and associated pipework feeding it would be normally be over sized so that it does not restrict the air flow.
Forced Induction
Individual throttle bodies work with turbo charged and supercharged applications and provide the same benefits to the engine and driver as normally aspirated.
A forced induction engine will still require a plenum chamber to feed the pressured air from the turbo to the cylinder with the throttle bodies sittin between the plenum and the head.
To monitor boost pressures to the engine a take off is required after the throttle plate, this is
It is possible to run Anti-lag with individual throttle bodies by using an air bypass valve which feeds air into the runner behind the throttle valve.
Throttle bore
The bore of the throttle body makes a significant difference to the way the engine performs. If the throttle bore is too small then this will restrict airflow at high RPM but if the bore is too large then this will lose torque in the lower to mid-range RPM. Therefore it is critical to consider what the engine will be used for and what sort of performance characteristics are wanted from the engine.
When sizing your throttle bodies we would recommend as a guide the following is used as a starting point, however, engine characteristics, intended use and rev range etc will all play a part in determining the ideal throttle diameter for an engine. Even the same basic engine tuned using different parts may require different throttle sizes to get the best performance. Also, remember that bigger is not always better.
| Engine Size | Throttle Size |
| 1.6 Litre | 42 mm or 45mm |
| 1.8 Litre | 45 mm |
| 2.0 Litre | 45mm or 48 mm |
| 2.5 Litre | 50 mm |
| 3.0 Litre (Straight 4) | 55 mm |
| 3.0 Litre (v6) | 48mm or 50mm |
The following table is guide based on cylinder capacity. Again there are other engine characteristics that could affect the best throttle size for a given engine.
| Cylinder Volume | Throttle Size |
| 400cc | 42 mm |
| 450cc | 45 mm |
| 500cc | 48 mm |
| 0.655 | 50 mm |
Runner Length
The length of the inlet tract also plays a large part in the performance characteristics of an engine. If the inlet is too long then this has the same effect as having to small a throttle. This is due to the buildup of friction between the inlet walls and the air slowing the air down and restricting its flow.
If the inlet is to short then the engine will suffer from poor low to mid-range torque due to the lack of airspeed and dynamic filling of the cylinder.
The overall inlet length from the inlet valve to the start of the inlet tract also plays a part in maximising performance, this is due to a pressure wave that is created when the inlet valve is closed but the air in the inlet tract, the momentum of the air hitting the shut valve starts a pressure wave that travels up and down the inlet tract. The intention of a tuned inlet length is to have the pressure wave arrive back at the inlet valve as it starts to open, this then provided a dynamic fill and increased the engine volumetric efficiency.
It is import to note that the tuned inlet length is based around a given engine speed, therefore, the inlet length should be determined based on the same parameters as the exhaust and camshaft so that it creates a tuned system to maximise the performance benefits at the given RPM.
Injector Position
The general rule with the injector position is the higher the revs the further from the inlet valve is should be. This is to allow the air and fuel more time to mix prior to it getting to the cylinder.
There are of cause some limitations with this rule and this is at low engine speeds. If the injector is too far from the inlet valve then the fuel can condense against the walls of the inlet before it reaches the cylinder. If the application is for a race engine that will always be used at high RPM then this is less of a problem, but with road cars that need good mid-range drivability then the injector positioned closer to the head would improve the drivability.
In extreme cases, injectors can be installed outside of the inlet tract altogether and set to inject straight down the runner.
The interaction between the injector and the throttle plate can also be beneficial. As the air passes over the throttle plate it is disturbed and causes turbulence which helps with the mixing of the air and fuel.