Chris Fairbrother has an idea for an all new sportbike, something very fast and easy to maintain, that doesn’t have to rev high to produce major power; hence large displacement (2300cc).
Oldsmobile, with assistance from Jim Feuling, developed an engine in 1988, the 2.3 liter, iron-block, four-valve DOHC aluminum-head Quad 4, putting out about 180 horsepower and tunable for much more. It was a popular race engine in the early 1990s and AJ Foyt had one up to 266 mph. Chris thought, hmm … sounds like a Quad 4 might do it.
Actually, Chris has plans to build his own engine, too, but the Quad 4 seems like a nice proof of concept before going off in that direction. He took a Quad 4, replaced the fuel injection and reversed the engine so the four 50mm flat slide carbs face forward (ram air). With raised compression, worked heads and race cams it will produce approximately 300hp. The bike itself is very small. Wheelbase 57.5″, seat height 30″, fork rake 26 degrees, weight approximately 360lbs, lean angle 55 degrees.
One of the biggest problems with the prototype was to build a frame that was very light and very strong. I opted for a backbone type frame, and used both the engine and gearbox as stressed members. The torque produced by the Quad 4 is substantial and I wanted to come up with a steering head capable of taking the forces, plus a stirrup unit that would hold the rear swingarm tight and prevent shearing. A mechanical engineer friend of mine modeled my frame on a computer and determined that, if anything, it was overbuilt.
What you see in these photos is the prototype, wooden forms show the shape of the tank and fairings which will be fiberglass and aluminum.
I knew from day one that I would have to design my own engine (which I have done) to use for production purposes, the Quad 4 application was simply a way of testing. My engine is an in-line four, four valve per cylinder, oval port, twin overhead cam, 1900cc with 30 degree valve banks, straight induction (between the cam banks) with studs anchored in the cylinder head passing through the block and oil pan, (ie. nuts torqued from below). This changes the usual approach somewhat, but adds rigidity to the whole motor. Assembling and disassembling is also simpler.
Looks like we have a modern Munch Mammut in sportbike form, though the engine size is hardly out of bounds in today’s ever growing motorcycle engine displacement race. I like Chris’ idea. He’s currently lining up financing to complete the project and take it to the next level but he’s already done quite a lot. I’ll be interested in following this as it progresses. Very cool project.