To people like you and me, Individual Throttle Bodies (ITBs) are very special things. They are the Mona Lisa of the car world. Pure automotive art. But other than just looking good ITBs also serve some other purposes too.
In most gasoline engines there is a single throttle body, or valve, that controls the amount of air that enters the engine. Vehicle manufacturers often use a single throttle body because it is less complex but more importantly it is also cheaper. Individual throttle body set-ups simply have a valve per cylinder that are linked to operate together.
A host of manufacturers have adopted the technology at some point but most notably perhaps is BMW, who commonly used ITBs on its famous naturally aspirated M cars.
The BMW E30 M3 was built to race and came ready equipped with ITBs
So other than the looks and the heavenly noise they generate what are the benefits? The two key ones are more power and better throttle response.
Let’s tackle throttle response first. With a single throttle body, when the driver presses the throttle pedal the valve opens and air is sucked into the plenum chamber (commonly known as the intake manifold) due to the vacuum created by the piston in the combustion chamber. The air then has to travel from the plenum chamber to the cylinder whose inlet valve is open. By replacing the main throttle body with individual throttles, the throttle can be placed much closer to the inlet valve. This means the plenum chamber, which is now upstream of the throttle body, is continuously full of air. This ultimately means the air has less distance to travel so the engine picks up sooner, which is translated to the driver as better throttle response.
Now for power. The improved airflow mentioned above helps to fill the combustion chamber more efficiently more of the time, translating to more power. The additional overall area of ITBs over a single throttle body also means there is much less restriction in the intake system.
However, a word of caution for anybody hurryingly clicking on Google to find a set of ITBs for their own car. I owned a Mk1 MX5 with ITBs, they were already fitted on the car when I bought it along with a receipt for over £3000 for the conversion. There was also a rolling road print out showing an increase of 5bhp over standard… Yep, five. The reason being is that ITBs require other supporting mods to make the most of that improved airflow. You have to make sure it enters and leaves the combustion chamber efficiently. So you will also need to port the cylinder head, use performance camshafts and run exhaust headers to get any noticeable increase in power.
ITBs on my own MX5 – its bark was far worse than its bite