Penske Racing Shocks 7800 Series - Manual (Page 9)

9
Dyno Graph Overview
An easy way to help picture what is going on here is to relate the graph’s shape to
what the dyno is doing to the shock. The dyno uses a scotch yoke system (shown
above), where the motor turns a crank and the sliding yoke allows the main dyno
shaft to make the up and down movement at the preset stroke. The dyno software
takes thousands of measurements throughout a single revolution of the crank. The
sampled points are connected to form the graph. By relating the crank’s position to
the corresponding graph quadrant and the circular crank movement may help in
reading the graphs.
QUADRANT #4
This quadrant begins
with the rebound valve
stack open. Where the
graph crosses the zero
line (inches) in quadrant
#
4
is the maximum force
produced by the rebound
valving. As the shock
approaches the full ex-
tension point, the re-
bound valve stack begins
to close as it approaches
the compression move-
ment. At this point the
cycle starts over again in
quadrant #1.
QUADRANT #1
This is the beginning of
the compression stroke.
Where the graph crosses
the zero line (pounds) in
quadrant #1 begins the
compression stroke.
Approximately the first
1/2" of displacement is
formed with relation to the
low speed bleed holes.
When the shaft reaches
a certain velocity, the
low speed bleed holes
shut off and the compres-
sion valve stack begins
to react.
QUADRANT #2
This quadrant begins with
the compression valve
stack open. Where the
graph crosses the zero
line (inches) in quadrant
#2 is the maximum force
produced by the com-
pression valving. As the
shock approaches the full
compression point, the
compression valve stack
begins to close as it ap-
proaches the rebound
movement.
QUADRANT #3
This quadrant begins with
the shock at full compres-
sion and the compression
valve stack closed.
Where the graph crosses
the zero line (pounds) in
quadrant #3 begins the
rebound stroke. Approxi-
mately the first 1/2" of
displacement is formed
with relation to the re-
bound bleed through the
piston. When the shaft
reaches a certain veloc-
ity, the bleed shuts off and
the rebound valve stack
begins to react.
REBOUND SHIMS
CLOSE AND
COMPRESSION SHIMS
BEGIN TO REACT
Low Speed
Bleed Holes
Through
Piston
Low Speed
Bleed Holes
Through
Piston
COMPRESSION SHIMS
REACT
REBOUND SHIMS
REACT
COMPRESSION SHIMS
CLOSE AND
REBOUND SHIMS
BEGIN TO REACT
P P P P P
O O O O O