Almost ten years ago I started designing a custom airbox for my R53 track Minis. It has been through a lot of revisions since then — different filter sizes, rear-port layouts, mounting schemes — but I have finally settled on this one.
I run JCW-style dry cone filters (3.5” ID flange) instead of the factory paper element. The box is shaped like a JCW unit without the rear noise port. More air, less restriction, and a lot more supercharger whine than stock.
The factory snorkel problem
The OEM cold-air snorkel never stayed clipped to the radiator shroud. Even when these cars were new — twenty-five years ago now — those tabs would pop loose. Both of my R53s had broken mount points at the shroud before I ever touched them.
Worse, the factory snorkel has a built-in NVH reducer — a resonator/silencer box that shrinks the air tract and kills intake noise. Fine for a quiet commuter. Wrong for a supercharged track car where you want every CFM you can get and you actually want to hear the blower.
I designed a replacement snorkel that enlarges the tube, removes the silencer, and adds a front section that snaps onto the core support so it stays put. I am thinking about opening the core-support hole further since the factory clip tabs are not used anymore anyway.
Early black prototype
The black airbox was one of my first working designs — printed in ASA, JCW-style blue dry filter, rear port that glued on separately. It worked, but the shape was a compromise and the snorkel connection was still a fight.
First-generation black ASA box with a JCW-style cone filter — MINI rocker cover visible behind.
Same era — circular outlet port and a side mounting tab. Lots of room left on the table.
Installed in the bay with an early red intake tube routed to the airbox.
Current airbox — v4
The current design is jcw_airbox_v4 in Fusion 360, printed in red ASA-CF. It takes a 3.5” ID cone filter — I run an Injen X-1021-BB (3.50” flange, 6” base, ~6.875” media height). Any filter with a 3.5” ID flange, ~5” base, and ~4” top works.
v4 in CAD — open rear, snap tabs on the lower factory airbox section, no rear noise port.
Printed shell — outlet tube and mounting tabs modeled in.
Filter clamped in — same JCW-style dry cone the box was designed around.
Interior bowl and filter flange — no factory silencing baffles.
3.5” ID flange opening — tape measure sanity check before committing filament.
v3 tapered the rear to clear cars with the plastic partition around the master cylinder and added rear tabs that hook the lower factory airbox section. v4 opens the rear completely and keeps those snap tabs — fits both partitioned and non-partitioned cars.
Cold-air snorkel
The snorkel is a separate print in red ASA-CF — three-piece tube plus a shroud cap that snaps into the core-support opening and connects to the airbox, not the throttle body. Same goals as the airbox side: bigger tract, no resonator, stays connected.
Snorkel shroud in CAD — wide mouth, no factory NVH box.
Tube split into printable sections — airbox side, middle, and shroud-side joints.
Front shroud seated in the radiator core-support cutout — no more popped clips.
Wide oval inlet behind the shroud gasket — room to open the hole further.
Front shroud flange at the airbox mouth — positive retention instead of hoping the OEM tabs hold.
Red tube mated to the factory rubber accordion boot at the airbox.
Can be run with the OEM shroud cap if you want to keep the factory look at the grille opening.
Installed
Both cars run the red v4 airbox and matching snorkel now. The whole air intake from the core support to throttle body tube is larger and straighter than stock — you hear it immediately.
Red airbox, red snorkel, JCW intercooler cover — the whole intake path in one shot.
Tube routed from the core support back to the airbox — no resonator box in the way.
On track at VIR North last year — you can hear the extra intake and supercharger noise through the helmet mic.
How to print it
| Setting | Notes |
|---|---|
| Material | PETG minimum — I used ASA for the black prototype and ASA-CF for the red parts |
| Airbox | Add manual supports around the filter lip on v3/v4 |
| Snorkel | Print with supports — four STLs (shroud, cold-air side, airbox side, cap) |
| Filter | 3.5” ID dry cone — Injen X-1021-BB or equivalent |
Download the STLs
| Part | Cults3D | Price |
|---|---|---|
| R53 airbox (v3 + v4 + early prototype) | R53 airbox | $50 |
| Cold-air intake tube / snorkel | R53 cold air intake tube | $40 |
Both fit R53 Mini and R52 Cooper S. The airbox download includes the original rear-port prototype (jcw_airbox_v1old), v3, v4, rear port, and battery support bracket STLs.