The exhaust manifold on a the 2.3L four-cylinder engine used in the Mazdaspeed3 sits at the back of the engine bay, as the motor is mounted sideways (transverse) due to the vehicle's front wheel drive configuration. The removal process is complicated by the fact that the stock exhaust manifold assembly will not easily come out of the engine bay, and thus requires removal of a few initial components in order to gain the necessary clearance.
Park your Mazda3 on flat ground, and remove the negative terminal on the battery. Use wheel chocks to block the rear wheels, and then using a hydraulic jack, raise your vehicle and set the front end on jackstands (refer to your owners manual to locate the factory designated jack points).
Use a 10mm socket to remove the factory heat shield over the exhaust manifold. Liberally spray the five 14mm bolts that secure the factory downpipe to the exhaust manifold, along with both O2 sensors with penetrating oil. It is highly advisable to repeat this process a few times, particularly if your vehicle is exposed to snow and salt in the winter.
Remove the windshield wipers and the wiper cowl. To do this remove the cap at the pivot of the wiper arm with a flathead screwdriver, then the single securing bolt holding the wiper arm to the wiper motor. Remove both wiper arms and set them aside. Remove the wiper cowl by removing the three top bolts, and the two side bolts alongside the ends in the engine bay.
Remove the 10mm nuts securing the heat shields on the lower side of the downpipe, and remove, followed by the 12mm bolts securing the downpipe brace to the exhaust tunnel of the car. Remove the O2 sensor which sits at the exhaust manifold collector with a crescent wrench.
Remove the four bolts securing the turbocharger to the exhaust manifold, and then remove the ten 14mm bolts which secure the exhaust manifold to the engine head. Slide the exhaust manifold off the manifold studs on the engine head, and then remove from the engine bay.
