Honda Fit (GE8) Stock Airbox Intake Restriction Mod

With the engine off and cool, remove the resonator cover and trace where fresh air feeds the primary filter chamber. On the GE8 the inlet passes below the resonance chamber and chokes down to a square throat measuring a little under 2 inches per side, which is the bottleneck this mod targets. Note where the molded internal divider sits, since it partially blocks a clean path to the wall you will open up.

Unclip the lid, release the intake ducting, and unbolt the box from its brackets, keeping every mount and fastener for reassembly. The box lifts out with the factory bracketing intact, so you are only modifying the box itself, not replacing any mounting hardware. Move it to a bench where the cutting stays clean and plastic shavings never reach the engine bay.

On the bench, identify the flat wall just past the internal divider, where enlarging the passage gives the straightest shot into the primary filter box. Fit a hole saw to a drill and cut a fresh opening at that spot. Work slowly so the bit does not grab and crack the plastic, and start the cut from the smooth outer face where you can.

The molded divider inside the tube still obstructs the new route, so cut it back with a fine-tooth saw blade to open the airflow path. Deburr and smooth the cut edges with a hobby knife followed by progressively finer sandpaper. The leading edge of the divider is awkward to reach; clean it up as much as practical and accept a slightly rough finish there rather than thinning the wall.

Wash every shaving and all sanding dust out of the box so nothing can be pulled into the filter. Once it is dry, coat the reworked interior with Krylon Fusion, a paint formulated to bond to bare plastic, to hide the sanding marks and seal the cut surfaces. Let it cure fully before going any further.

Cover the underside of the box, the face closest to hot engine components, with two layers of aviation-grade heat-reflective aluminum tape to keep radiant heat out of the intake charge. Use genuine heat-reflective foil tape rather than kitchen aluminum foil, and press it down so it conforms tightly with no lifting edges.

Bolt the box back to its mounts, reconnect the ducting, and clip the lid into place. With the enlarged inlet, the factory underhood scoop that draws air from behind the front bumper now feeds directly into the new opening instead of the general area around the box. To keep the mod hidden, refit the resonator chamber lid and the engine bay looks stock.

Rather than enlarging the box, several owners cut the MAF/MAP tube out of the stock airbox lid and joined it straight to the throttle body with a 2.5-inch silicone coupler, since the outlets measure 2.5 inches; some add a 90-degree elbow and a second coupler in place of the built-in bend. Reusing the factory tube is deliberate, because it preserves the exact inside diameter the sensor expects. Keep the original mounts bolted in, and once the lid clips on and the coupler is clamped the assembly sits solid.