Game Boy Road Engine

1992 The Code Monkeys

Platform: Nintendo Game Boy

Back in 1992, The Code Monkeys already had official Game Boy dev kits and experience from writing Missile Command and Centipede for Accolade. Towards the end of the year between projects, developer Mark Kirkby began experimenting during downtime. A massive fan of Stunt Car Racer on the Atari ST and Amiga, he wondered whether something similar could be achieved on the Game Boy.

Mark therefore developed an early prototype road engine, designed to simulate elevation, jumps and gaps – something rare on the Game Boy due to hardware limitations.

“Most existing Game Boy racing games relied on modifying the X-scroll register on each scanline to show turns in the road which produced a very flat-looking track.” explained Mark. “I realised that by instead manipulating the Y-scroll register per line, skipping or repeating VRAM lines, I could create the illusion of elevation, making the road rise and fall.

After some experimentation, the approach worked well enough to continue with. I began prototyping the demo you see here. I chose motorcycles over cars because of the Game Boy’s scan line sprite limitations; bikes, being narrower, fit better on a scanline. I also added features inspired by Stunt Car Racer, such as jumps and pits.”

The demo was never intended as a full game – just a proof of concept to secure a publishing contract. To protect their engine from being copied, Mark and his team went to quite some extreme lengths:

“We purchased three new Game Boys, disassembled them, hardwired in 64K ROM chips, and filled the cartridge slots with epoxy resin so they couldn’t be opened or dumped. These modified systems were then sent directly to publishers… The unit we sent to Ocean ended up sitting on Gary Bracey’s desk for about two weeks while he was on holiday. When he returned, he powered it on, saw the demo running, and contacted us right away to offer a deal.”

The rest his history, and Mark would create Road Rash on the Game Boy for Ocean Software. Unfortunately, Mark confirms that the engine never got used anywhere else – they continued to try and pitch it, but had no takers.

Decades later in 2025, Mark got in touch after seeing a video we posted about a Game Boy Road Rash prototype by Tuna Technologies and mentioned about having done his own road routine which was extremely similar. Weeks later in September 2025, Mark got in touch again with Games That Weren’t to share the prototype with the wider community:

“I managed to drag out the final floppy I had with that code on it and it read fine, so I managed to get it uploaded to GitHub. It contains the original source code (dated Oct 1992 in the DMG files) which I managed to get assembling using the original Nintendo assembler through DosBOX and managed to recreate a ROM which can be run in the emulator or (hopefully), original Game Boy.

I also included an original design document with the quote for the work and a readme that covers the background, instructions and details for the engine and how we got the Game Boy Road Rash contract.”

Thanks to Mark’s efforts, the prototype is now preserved and accessible. You can play the demo in an emulator – or even on original Game Boy hardware. The bonus is the complete source code, including assembler files, design documents, and batch files needed to recreate the ROM – meaning that potentially further games could be created with it!

With thanks to Mark Kirkby for sharing both his story and his work!