The engine compartment of the Protege as it was delivered to Mazda. An intake duct utilizing a K&N cone filter was produced for the car, and it got close to production when Mazda discovered that, due to it's narrow range of operation, the engine management system could not tolerate drawing warm air from the engine compartment. It was not possible to design a filter system that drew truly cool air in the time available. This aside, obtaining measurable improvement with this type of intake was proving to be a challenge.

A prototype header was also produced for the Protege. The Protege is equipped with a catalytic converter located directly under the stock exhaust manifold, which makes the production of a conventional design header rather difficult. In an attempt to discover if the 2.0 engine responded to a "conventional" header design, a rather unorthodox looking header was fabricated to test this premise. In order to extend the header primary tubing to the desired length, the primary tubing on the prototype header was wrapped around the upper radiator hose, then routed down to the catalytic converter. This design stood little chance of making it to production, but subsequent testing confirmed our beliefs that the catalytic converter was a "power-robbing" source. This header was not included on the prototype delivered to Mazda.