Budget R53 Cooper S Airbox Modifications
There are several affordable modifications that can improve airflow on the standard R53 Cooper S airbox. This is a write-up of the budget-friendly modifications performed by @r53budgetbuild and @R53HomeBrew.
Modification Overview
- Open rear of airbox for scuttle panel air intake
- K&N filter adapter installation
- Enlarged intake opening with stainless reducer
- Filter – K&N RU-3190 Universal Air Filter Rubber 2-3/4″ 20 Degree Flange 4″OD 6″H
Stage 1: Rear Opening & K&N Filter
The first modification opens up the rear of the airbox to draw air from the scuttle area, similar to the JCW airbox (although the JCW version includes a valve). This was achieved using 3D printed parts:
- Rear opening parts: Thingiverse – Airbox Rear Opening
- K&N filter adapter: Thingiverse – K&N Filter Adapter
📸 View the initial build on Instagram
Stage 2: Removing the Restriction
We couldnt help but think that the 3D printed K&N adapter was creating a restriction.
Stage 3: Stainless Steel Reducer Installation
Keeping with the budget theme, a stainless steel reducer (OD 63mm to 70mm) was sourced and installed to provide a smooth, unrestricted intake opening.
Installation Process
- Remove the airbox from the vehicle
- Use a Dremel with a cutting disc to enlarge the airbox opening (Or an angle grinder like we did being impatient)
- If you can swag the ends of the pipe
- Test-fit the stainless steel reducer
- Bond the reducer in place using Gorilla Epoxy glue
- Allow to cure fully before reinstallation
Parts Required
| Item | Specification / Source |
|---|---|
| 3D Printed Rear Opening | Thingiverse STL files |
| 3D Printed K&N Adapter | Thingiverse STL files (optional – later removed) |
| Stainless Steel Reducer | OD 63mm → 70mm |
| Adhesive | Gorilla Epoxy Glue |
| K&N Filter | Standard K&N cone filter – K&N RU-3190 |
Benefits
- Improved airflow: Larger, smoother intake path reduces restriction
- Scuttle panel air source: Draws cooler air from outside the engine bay
- Budget-friendly: Uses affordable materials and 3D printed parts – now for the rear part only
💡 Tip: If you don’t have access to a 3D printer, The box can be purchased with a K&N Kit (unsure about the open back) from the regular mini performance part retailers
💭 Summary: A cost-effective airbox modification that improves airflow through a combination of 3D printed parts and a stainless steel reducer done on a budget
