I've been looking for a way to affordably install quad throttle bodies onto my 206 GTi. After seeing prices on professional systems, I decided I would have to build my own. Butterfly type ITBs would be very difficult to design and build, due to the tricky axle which needs to run between each body. I thought of a way around this, and it turns out so did many racing teams through the years. The slide throttle. BMW used these for racing on their e30 M3. Here is a picture:
Why aren't these stock?
The reason they aren't used for road vehicles very often is that the overlap of the two circular cutouts as they move changes area in a very non-linear pattern. This gives the accelerator an "on or off" feel. This makes taking off WITHOUT frying the tyres difficult.
Why use a circle?
Throttle bodies and intake systems are always circular to allow a vortex to be formed. In the days of carburettors, a vortex was created by having a perfectly circular tube before the carburettor to mix the fuel into the air more effectively. With fuel injectors, the fuel is sprayed in tiny particles, so mixing is not an issue. The use of a vortex actually impedes the flow of air, since centrifugal force increases the density of the air on the outside of the tube, where there is surface friction. A vortex also creates turbulence when it turns a corner, such as in the engine head. That is the reason PSA intakes such as the one in my car change between circles and ovals for the cross section of piping, to stop vortexes and allow laminar flow. The only advantage to circular piping with fuel injection is that it has the smallest possible ratio of surface area to volume, to decrease friction.
My idea is simply using a square pattern for my throttle plate's cutouts, which has the advantage of creating laminar flow, the disadvantage of a slight increase in friction against the sides of the duct, and the huge advantage that the throttle response will be almost perfectly linear, even more so than the stock butterfly valve. Here's my current design, almost ready to send to the CNC machine (which I have yet to find one to borrow, maybe my uni has one I don't know of...)
Let me know what you guys think, and please tell me if I'm mistaken about something and will destroy my engine by trying this