GoogleCustom Search

Goldmember Custom Bike

The concept of this bike was to further merge the performance and custom worlds; to build a bike which could compete in both venues. The challenge was to find a balance between a functional race bike , which should be powerful, durable, aerodynamic, with everything accessible and easily serviced … and a full custom bike, which must be visually stimulating, unique and possibly risky in design.

I was determined to push the single cylinder (from a modified V Twin ) concept to it`s limit, still using the rather privative air cooled two valve push rod design . Adequate cylinder filling is a major issue in producing substantial horsepower in single cylinders, which do not have the aid of air flow into through and out of other cylinders to help .

Trying to do more with less was definitely a big factor in the design of this bike. The engine was rotated backwards 15*as well as rearwards , closer to the transmission to keep things compact. A rear head was fit to the front cylinder, allowing the induction system to transfer up and over , to allow adequate plenum chamber volume. Pushrod angles were changed and a special camshaft were required to accomplish this. Exhaust port angle was changed as well as raised to aid flow.A three step pipe gets rid of exhaust, built to have great top end power without sacrificing much bottom.

The belt driven Rotrex supercharger feeds an intercooler before a 54mm throttle body, manifold and forward facing intake port, where the single high volume injector is located. Boost is produced in the 22 to 23 psi range, a relief valve controlled it somewhat and protects against excessive levels when throttle closes. The main fuel pump is in the tail section mounted fuel tank, a boost sensitive regulator increases fuel pressure one to one with boost pressure. A similar pump and regulator do the same thing for the fuel side of the nitrous oxide system. A Thundermax ECU is specially configured for this combination, and a Dobec boost sensitive module is patched in to supplement fuel under boost Cylinder bore is 4.125” and stroke is 4.4 “. Intake valve size is 2.020” , exhaust 1.75”.

A Baker six speed transmission has a low first gear , and close top gears. A pingle electric shifter is used , allowing rear foot pegs to be mounted far rearwards. The transmissions mainshaft was shortened as well as clutch pack and primary belt narrowed to bring it down to 2” wide from Primo/Rivera 3”system.
A chromolly frame encircles the engine and transmission, largely 1” diameter. Double top rails/backbone allow room for induction system. A slightly larger diameter neck houses a hidden shock for the front end inside it`s stem.The girder style fork was cut and machined from 1” steel plate . The top link rocks on a pivot and works the shock assembly.

Partly for visual reasons , a large 23” rim and tire are used in the rear, but also I found that land speed race bikes prefer a large diameter, narrow wheel… makes for a longer , narrower footprint and catches less air inside the rim. A 19 “ rim sits in front , still a large size, yet dwarfed by the 23” in the rear.

Both rims surround “drum hubs” which were inspired by the large hubs of the pre disc era race bikes. A 12” unit is in the front and a 13.75 “ out back .Both house a stainless disc and a four piston brake caliper. The hubs and outer plates were manually machined, the rear hub itself was turned from 98lbs of 14” 6061-T6 aluminum, down to a 18 lb part.

Bodywork on the bike is all hand formed aluminum. Under the transmission sits a belly tank which stacks the engine oil and supercharger traction oil reservoirs.

The bike was brought to Bonneville with less than a mile on it, where we spend days working out clutch, shifter and fuel injection issues. On the last day of the event(BUB Speed Trials) , it made it`s best run. After hitting a false neutral about half way into my two mile run in and almost coasting to a stop, I got back on it and had to run through my timed mile still accelerating… not really the idea in land speed racing, but this was my last chance. The bike averaged 154.8 mph through the mile, exiting 10 mph faster than that, shooting ducks the whole way as the nitrous system was still running far richer than ideal. The fun part is doing it with half of an old air cooled pushrod design, make something go fast that really isn’t supposed to Racing at Bonneville is all about dealing with all the many challenges as they come up, and there are many with a new bike, as well as the salt was very wet and the weather unpredictable in `07.

While the first chapter in this bikes story is complete, it will again race at Bonneville, but not before a few repairs and upgrades .In between though, it will surface as a street legal custom… headlights, tail lights, mirrors etc .The bike will compete at this years World Championships of Custom Bike Building, it likely will be a little mis-understood in the largely ornamental world of custom bikes… but at least it will have a story to tell…