OK, so lets build a Top fuel bike

Over 3 years ago now - around July 2019, i made a start on designing a top fuel bike. I knew roughly what i wanted to do, and so set about gathering information and finding out if it was possible. 

The brief was simple - to build a relatively light and simple fuel bike that makes the most of the latest technology - and to get away from the ever increasing trend of bigger, heavier and more.

I did a lot of research into power and weight ratios, bore and stroke ratios, fuel calculations, parts availability, and sketched page after page of ideas for several weeks, and slowly but surely a plan came together. As with anything bespoke, if you want it to be the way you really want it then it's bound to be the option that requires the most work, and also be the one thats the most challenging to build. Mostly because practically none of the parts are out there to just buy off the shelf (not like i had the budget to do that anyway). 

But i thought hey - i've got the shed of dreams, I've waited my whole life to have a workshop like this, think big!

And so - in order to keep it to the breif - Light - simple - trick i made the following decisions:

• To keep it light - no blower, no jackshaft, no gearbox, no huge rear wheel and tyre, no enormous clutch with weights, arms, and release bearings/cannons.

• To keep it simple - no blower, no jackshaft, no primary drive and belt, no gearbox, and no horrendously complicated mechanical fuel injection.

• To make it trick - It would use the latest and most powerful electronic ignition i could find, it would use electronic fuel injection with huge injectors, and use a 100% pneumatic - CO2 clutch, all controlled by the most suitable and adaptable ECU i could find. 

Without a blower the engine would need to have a large capacity, and to do away with a primary drive it would need to be narrow enough to mount a clutch and drive sprocket directly on the crankshaft. A v- twin was a possibility, but to rev high at 3000cc+ would need a bore so big that pistons aren't commonly available. A v-four however works out nicely at common bore sizes and relatively short stroke, and would still end up narrow enough to fit a cluch on the end. Cylinder head layout and valve components would be based on the V&H 2v suzuki prostock head fitted to my funnybike, but with roughly the same valve sizes it would be possible to fit 4 valves per cylinder.

I went for a 360 degree crank design, as 180 cranks can be prone to a 'rocking couple affect' across the length of the shaft, and with such huge pistons and counterweights i thought i'd steer clear. 90degree vee - 360 crank also has a nice even firing sequence of 90-270-90-270.

 

 

The engine would be a 90 degree V4 with 3023cc displacement and a bore of 111,125mm, and stroke of 78mm.Would use DOHC and 4 valves per cylinder 38mm exhaust and 45mm Intake.  Pistons and sleeves being common big block top fuel and top methanol sizes. 

With those decisions made and drawings done, all that was left was to figure out was how to actually make it - as you can't buy an off the shelf 3000cc V4 top fuel bike!