INLET AND INJECTORS
On the other side of the engine, the inlet manifold choice has also improved drastically over the years.To start with the RS500 eight-injector manifold was a must, then the Swedish-style inlet was everyone’s fancy, and now nearly all big-bhp YB builds feature a Hart inlet. There are slight differences in performance between them, but all that really matters is that they all perform much better than the standard inlet which becomes a restriction at around 500 bhp. Roller barrel throttles have also been used to good effect in many applications, but as they were only ever designed to work on 300 bhp WRC cars when you start to push enough air for over 500 bhp through them they don’t like it. Another option is to fit a set of individual throttle bodies which can be used with a plenum chamber – these will have performance advantages but considering a single throttle body gives such good results they are only used when people are looking to squeeze out every last bhp possible.
The traditional route of replacing injectors was to go for the next size up in the Bosch range. The first step is dark greens or 803s, capable of 300-330 bhp, costing around £100 each from trusted sellers such as Burton Power. Continuing up the colour-coded Bosch items are ‘light-blues’ or 400s, which are good for up to 400 bhp, then ‘greys’ or 403s, which supply the juice for 400-450 bhp.
Sticking with the Bosch injectors but wanting more than 450 bhp involves simply adding more of them, another four in fact. This utilises the RS500’s or WRC-style eight injector set-up. Eight ‘greens’ will provide enough fuel for over 500 bhp, but the for ultimate power eight ‘greys’ will be needed.
However, more sophisticated modern engine management systems and improved injector designs means that you can buy items that will deliver over twice as much fuel as a set of ‘greys’, so there’s no need to add the complexity and expense of an eight-injector set-up. Traditionally larger injectors were more difficult to control at lower engine speeds, so two sets of smaller injectors were the preferred method of ensuring low-speed driveability coupled with peak power potential, but modern injectors are much more capable of delivering at both ends of the scale so offer a neat and simple-to-install alternative.