Performance engine tuning is largely a matter of identifying the items that restrict the power output of the standard engine, and producing simple, cost-effective solutions to overcome those weaknesses. One of the fundamental limitations of the Rover K'-series 1.8i engine, as fitted to the Lotus Elise, is the relatively small bore and convoluted shape of the pipe upstream of the air filter, which severely restricts airflow.

Raceline's Performance Engineered modified air box eliminates this restriction, as by doubling the bore of the pipe the surface area is increased four-fold, allowing a huge increase in airflow. This alone is sufficient to increase power output by some 3-5bhp when used in conjunction with the optional Pipercross foam filter element, although the standard Rover paper filter element may be retained if preferred. Furthermore, by connecting the air box directly to one of the Elise's side ducts, we also benefit from a modicum of ram air effect. Because of the difficulties of testing this under dynamic conditions any performance gain is impossible to quantify, but in back-to-back comparisons the difference can clearly be felt. Perhaps more importantly, the air drawn from outside the car is cool.

Although the standard air box draws air from the general vicinity of the side duct, it still breathes from within the engine compartment, and as we have discovered, temperatures within the Elise's fully-enclosed engine bay can become alarmingly high. For the same reason we rejected the option of using a simple cone filter, as a number of other tuners have done. A cone filter shows similar gains on the dyno, but once installed in the car the cone filter again suffers from the drawback that it draws heated air from within the engine bay, negating much of the benefit. We also felt the noise penalty inherent with a cone filter was too great for ordinary road use, especially bearing in mind the location of the engine, right behind the occupants.

The optional Pipercross foam filter element is available separately and can also be installed with the standard air box if desired. While this will produce a small gain in airflow and overall efficiency, any performance gain will inevitably be slight. For maximum gain, the filter element and modified air box should be used together. The provision of copious quantities of cool air, and the elimination of any restrictions in the inlet tract, work both theoretically and in practice to produce a benefit you can really feel.