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A stock cam is on the left, a 268
degree duration cam with a .600" lift is
on the right. |
Selecting the correct camshaft
for
you bike can be confusing and frustrating. The
more popular cams available may not be the right
cam for the way you ride or the type of bike you
have. A cam that is installed in a show bike
featured by the 'biker' magazines may not be
part of a proven engine performance combination.
When it comes to improving your bike's
performance by installing a cam, you should deal
with a reputable performance shop and a proven
record on improving power.
In order to get the best performance,
the camshaft must be matched to all the other
engine components. The combination of
carburetor, intake manifold, head design, flow
characteristics, valve size, bore, stroke,
compression ratio, ignition system, exhaust
system and the way you are going to ride the
bike all have an impact upon the best cam to
select. If head work or pistons are not in your
budget, then your choices are limited to bolt-in
cams. Even limiting your cam selection to a
bolt-in cam provides you with a wide choice of
options. Most bolt-in camshafts are intended for
use with bikes and engines that have few
modifications. The minimum requirements for a
bolt-in cam is usually a re-jetted carburetor, a
high-flow air cleaner and a less restrictive
exhaust system.
Make sure you match your riding style
or needs to the the horse power and torque
characteristics of the cam. The biggest mistake
made in cam selection is getting to much cam for
the bike, the way it is ridden or the components
on the bike. A good set of pipes, some minor
upgrades to the CV carburetor, a good ignition
system and the right cam can produce around 75
HP when properly tuned.
If you ride a heavy bike
like a Road King or always ride two up, you
should place more emphasis on having the engine
produce good low end torque. If you have a light
bike like an FXR or Dyna, and you want a lot of
top end power, a mid-range power cam can be
used. If you usually ride your bike in town,
choose a camshaft for low end torque. If you
have your choice between horsepower or torque
for engine characteristics, the best decision is
to go for the torque cam.
As a general rule,
cams with 220-235 degrees of duration tend to
produce good low end torque. Cams with 235-250
degrees of duration tend to work best in the
mid-ranges and cams over 260 degrees work best
for top end power. Camshaft overlap duration
less than 30 degrees tends to produce good low
end power. Lobe Separation Angles (LSA) of
100-103 degrees tend to produce power at the low
end.
Cams
with valve lifts .500 inches and under, with a
duration under 250 degrees are generally
considered bolt-in. Cams over .500 inches lift
and 250 degrees duration require increased
compression and head work to work best.
Don't think you are going to take your
stock bike
and
turn it into a 100 HP monster by adding a cam,
replacing the carburetor and putting on straight
pipes. Getting an 80 inch Big Twin engine to
produce 100 horsepower at the rear wheel is
difficult, time consuming and quite expensive.
You are much better off bolting in a Crane
Fireball 310, an Andrews EV-27 or a V-Thunder
EVL-3010 in your street bike than trying to find
a long duration cam because you have been told
'bigger' cams makes more horsepower. A well
designed and tuned engine combination, using a
mild bolt-in cam is quite capable of
embarrassing most other Harley's between
stoplights. 100 horsepower is not very useful if
the engine does not make power until 6000 RPM.
Harley-Davidson Big Twin engines were not
designed to take that kind of abuse. An engine
with 70 HP at 4800 RPM and 85 foot pounds of
torque at 3200 RPM can be a real thrill compared
to a stock EVO motors. |