In the last segment we looked at the very basics of an Individual Throttle Body setup, and the very basics by which it works. This time around I wanted to go a bit more in depth and explore the different types of setups out there. I’m also going to attempt to give some insight into various technical features of each type as well.
Trumpet type – this is the image that most people have in their head when they thing of an Individual Throttle Body. Each airhorn, or trumpet is responsible for feeding an individual cylinder. However simple it may seem, the design of the trumpet itself has a tremendous amount to do with the performance that can be extracted from it. First, there is the length of the trumpet. Just like in a sealed intake manifold, the shorter the runner, the more top end power the engine will have, and the longer the runner, the more low and midrange power it will have. Altering the design of the bell also has alot to do with the overall powerband as well. These are the most simple type out there, as they use a simple butterfly valve to ingest air to the combustion chamber. There are several key elements in the design one chooses for their trumpet style. These will vary from engine to engine based on many factors, such as combustion chamber design, valve placement and diameter, cam lobe profile, etc. The proper taper of the trumpet will give you the best of all worlds – sufficient low speed volume so the car doesn’t become peaky, but providing significant velocity when the valve is fully opened, to mid and top end power. The trumpet design as mentioned, is highly interdependant on many other aspects of the engine. If anyone is interested in some helpful math formulas, let me know and I’d be happy to post them.
The above pictures shows a typical trumpet style ITB setup on a modern V6 engine. Note the taper of the trumpet that continues to the intake runner itself, providing a balance of low, mid and top end performance.
Slider ITB – Slider style throttle bodies were born out of logical belief that with the traditional butterfly valve style, you are giving up prescious air volume and velocity by having a shaft in the center of the bore. In a slider ITB, there is no throttle shaft. Instead, there is a door that slides open and closed to ingest air. As you can imagine, the packaging requirements tend to make these more space hungry and more expensive to produce. These are also said to give non linear throttle response, making them difficult to drive at lower speeds, and difficult to maintain a steady state speed.
Typical Slider Type
Roller Style – the roller style throttle body is the third type of individual setup out there. In this type, you have two barrels, one that rotates inside another. These are essentially combining the linear throttle progression of a traditional butterfly setup, with the pure flow of the slider type. As you can imagine, these are the post costly to produce, and leave the least margin for error, as you no longer have the ability to alter runner length, taper, etc for a given application. Each component has to be machined on it’s own, meaning it’s got to be perfect out of the gate. The inner roller uses ball bearings for smooth and linear actuation.
Get your math right, your patience high, and a bunch of buddies to chip in on a CNC machine, and the roller is clearly the way to go from a packaging and performance standpoint. But there really is no margin for error.
Here is a very neat video showing a roller throttle body in action on an STi
So, now we’ve seen the different styles of ITB’s out there. In the next segment, we’ll get a bit more into design considerations of the most popular version, the butterfly style. This will include injector placement, trumpet location, and what all is needed to actually make one of these setups run a car.
Stay tuned!!!
Kwame
Z1 Performance
Jonathan
Corner Balance 