Honda Fit Exhaust Header Removal and Aftermarket Header Installation

Work only on a fully cooled engine so the manifold and pipes are safe to touch; doing the job first thing in the morning after an overnight rest guarantees this. Raise the passenger side of the car and set it on a jack stand so you can reach the manifold and its lower fasteners from underneath. Before wrenching on anything, coat the two upper studs and nuts and the three lower bolts with penetrating oil and give it five to ten minutes to work into the threads. Reapply penetrant to any seized fastener as you go.

Take off the metal heat shield that covers the manifold. It is held by three bolts, sized either 8mm or 10mm. Use hand tools rather than an impact driver, since these small fasteners can shear off if forced. Removing the shield also opens up the gap you will later feed a pipe or breaker bar through to reach the header nuts.

Freeing the header fasteners is the hardest part of the job because clearance is minimal and the threads corrode. Seat a ratchet with a 14mm deep socket on each fastener, then slip a one- to two-foot steel pipe over the ratchet handle to multiply your leverage. Apply smooth, progressive force instead of jerking, so you do not strip or snap anything; you will feel each nut suddenly break free. As an alternative reported by other builders, a 1/2-inch drive breaker bar with a deep socket worked from the top also does the job well.

The manifold is secured by two upper nuts on studs plus three lower bolts. Crack all five loose, but at this stage fully back off only the two upper nuts. Leave the three lower bolts threaded in place: removing them now would let the header's weight hang on the spring bolts that join it to the catalytic converter, and those spring bolts can bend under that load.

Follow the O2 sensor lead to its connector, which sits next to an engine-mount clip. Depress the release tab on the connector and slide the plug sideways toward the passenger side to part it; a hidden tab underneath is what stops it from simply pulling straight off. The lead also snaps into a bracket, so press the small tab beneath that clip and draw the plug toward the manifold to free it entirely.

From above, wet the two spring bolts and the header support bolt with penetrant and let it soak in. Then unthread the spring bolts a little at a time, alternating between the two so the flange separates squarely. Because the three lower manifold bolts are still holding the header, there is almost no load on the springs while you do this.

Go back to the lower fasteners and take out the three remaining bolts, then lift the manifold off the two upper studs. If you have already pulled those studs out, keep one hand under the header as the last bolt releases so it cannot drop. Recover the exhaust gasket and the donut gasket for inspection.

Move the oxygen sensor from the stock manifold onto the new header, using a crescent wrench and a dab of penetrant to break it loose. Be aware of a fitment quirk of the Weapon R street header: it is about half an inch shorter than the OEM part, so the factory support bracket no longer reaches it. Some owners flatten the bracket's mounting plate in a vise to bridge the gap; others leave the bracket off and rely on the header bolts and cat pipe for support. For reference, the stock header pipe measures under one inch of inner diameter while the Weapon R piping is roughly 1.5 inches.

Clean the exhaust gasket and the donut gasket and reuse them if they are in good shape. Inspect the donut closely, since a loose or poorly seated donut is the most common cause of an exhaust rasp after this job. If it is worn or fits loosely, install a new one; a donut gasket is cheap insurance against having to tear the exhaust apart again.

Slide the exhaust gasket onto the two upper studs in the correct orientation, then raise the new header into position. Start the two upper nuts and the three lower bolts by hand and leave them all loose for now. Keep a hand on the donut as you lift the header so it does not slip out of place.

Support the cat pipe and push it forward toward the header so the spring bolt holes line up, then start each spring bolt by hand. Turn them in alternately, drawing the flange together a little at a time until both are fully seated.

Plug the oxygen sensor connector back together and reseat it in its bracket. Tighten the header fasteners to the factory value of 33 lb-ft. Because the space is so tight, a compact or stubby torque wrench reaches the bolts far more easily than a full-length one.

Confirm everything is tight: the two upper nuts, the three lower bolts, both spring bolts, and the O2 sensor along with its connector and bracket clip. Start the engine and listen for exhaust leaks. If a rasp or buzz appears under throttle, suspect the donut gasket seating first; repositioning it has cured that noise for others rather than any fault in the header itself.