THE DIFFERENT TYPES

The most straightforward solution are ‘twin bodies’. On a four-cylinder engine this will be two pairs of twin bodies, much like the older twin carburettor set-ups. In fact, most of the time the older style inlet manifolds can be retained.Twin bodies can also be direct-to-head fitment. Direct-to-head bodies are as the name suggests, and there is no manifold between the throttle body assembly and the cylinder head. Instead, the end of the throttle body is machined to directly fit the inlet face of the head.

One major advantage offered by this system is the ability to tailor the angle at which the throttle bodies sit against the head.The angle of the inlet ports within a cylinder head will vary from engine to engine, and therefore the optimum angle for the throttle bodies to be mounted at won’t be the same for all engines. By machining the mounting face to suit the application, performance can be improved over those using an older carburettor-style inlet manifold which often sits at 90 degrees to the cylinder head. However, machining the mounting face of the throttle body is notoriously tricky, and means the design is only really suited to one application at a time.

The best, no compromise, solution is a set of single, individual bodies. Each cylinder has its own, standalone throttle body, and there is a separate manifold mounted between this and the cylinder head.This allows for much greater accuracy in terms of port matching to the cylinder head, and means a specific manifold can be machined to best suit the angle of the inlet port for a specific engine.The same throttle body can be used, while the relatively inexpensive manifold can be tailored to get the best possible performance for a specific engine or application.

Also, single bodies can be tailored in terms of size, shape, and length to achieve the best mixture path for the required application. Single bodies also have the option of running multiple injectors per cylinder, too.