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…
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