Subaru never set out to build a motorcycle, let alone a boat, but its turbocharged folklore has a way of leaking into other garages. The company chased glory on the Isle of Man with the WRX STI, while fans stared at that flat-four and thought, what if this thing powered something else entirely. Out of that gap between factory intent and backyard imagination came a one-off machine that started as a motorcycle-only stunt and ended up looking suspiciously like a tiny Subaru-powered ship.
From TT heroics to garage fever dreams
The modern myth starts with a blue sedan howling around the Isle of Man, not a custom bike on a stand. Subaru sent a Subaru WRX STI to chase the motorcycle-dominated TT course, with Higgins threading the car between stone walls and front doors on the Isle of Man. That factory-backed run, with Jun and Still buried in the fine print of development and logistics, turned a rally-bred four-door into a cult object for people who usually only cared about superbikes.
The spectacle was not just about lap times, it was about control at the edge. In one widely shared clip, rally driver Mark Higgins is seen calmly correcting a wild slide at roughly 150 mph, a moment that lives on in a thread where Apr user Talidel, tagged as Top 1% Commenter, jokes that There are people who watch the onboard and immediately want to go vroom themselves. That mix of terror and inspiration is exactly what pushed some fans to imagine the Subaru WRX STI engine not just in rally stages, but in anything with wheels, or maybe even without them.
The WRX engine that tried to be a bike
One of the wildest expressions of that obsession is the Madboxer, a custom build that stuffs a full Subaru WRX car engine into a motorcycle chassis. The builder did what Subaru never did, lifting the flat-four out of a sedan and hanging it between two wheels, then discovering that the sheer bulk of the boxer turned the project into something closer to a sculpted pod than a lithe bike. From some angles it looks like a minimalist dragster, from others it resembles a compact hull perched on tires, the sort of thing you half expect to float away if the road floods.
Design-focused coverage leans into that surreal profile, describing how the Madboxer, sometimes styled as the ‘mad boxer’, takes a Subaru WRX engine and pairs it with a Kawasaki fuel tank inside a bespoke shell. The result is one of the most outrageous custom motorcycles on record, a machine that visually blurs the line between bike, land-speed record car and, with its broad, flat bodywork, a tiny powerboat that never quite made it to the water. It is the logical endpoint of the motorcycle-only stunt teased in the headline, a fan-built answer to Subaru’s own refusal to stray from four wheels.
How Subaru’s TT weapon fed the “boat” joke
To understand why anyone would go to such lengths for a car engine, it helps to look back at how hard Subaru leaned into the Isle of Man. In one official onboard, recorded in Jun, the Isle of Man run is narrated in real time as the driver talks through the risk of having a massive accident, then getting back on power as soon as the car settles. Another factory video, also framed around Jun, walks through the STI used for the challenge, introducing the all-new 2015 WX STI and stressing that the Isle of Man is a bit of a special STI, built to soak up bumps that would terrify most road cars.
Subaru and the AC authority on the island did not treat it as a casual joyride. The company detailed how the speed limiter was removed from the car and how Subaru and the carried out a comprehensive risk assessment before letting the sedan loose on public roads. Later coverage of the record effort highlighted that Three-time British Rally Champion averaged 116.4 mph in a Subaru WRX STI Just Broke The Isle Of Man TT Record For Cars, a figure that put the four-door in the same whispered conversations as full race machinery that once crossed the Pond in a Rover SD1.
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