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Q: I
don't understand what you mean by a "gas assist."
A: Lets look at some simple principles regarding
this part of the shock function. When the shaft travels into
the body of the shock there has to space to occupy the cubic
centimeters of displacement which the shaft will occupy. Otherwise
it would hydraulic lock. A standard hydraulic shock will not
be completely filled with fluid, leaving an air pocket in the
reservoir area to contract and expand as the shaft travels in
and out of the body. Most racing shocks use one of the two methods
of gas-assist to occupy this space for contracting and expanding.
Q: Why
bother with gas; wouldn't the air pocket function just as well
without it?
A: The advantage of using gas is simply to stop aeration
of the fluid and air. The aeration would reduce fluid viscosity,
causing the shock to fade, weakening damping capability and building
heat. This would also reduce viscosity and further diminish damping
capabilities.
Q: What
are the two types of gas shocks and how does each function?
A: The two types of gas shocks are high gas pressure
and low gas pressure, which incorporates a gas cell. The high
gas-pressure system uses a mono-tube design, which means the
piston uses the shock body as its cylinder wall. Any dent in
the shock body and the shock will not function, because the piston
will be pinched by the cylinder wall.
This design requires a second piston which
floats in the cylinder to separate the gas from the fluid. Some
high-pressure shocks don't use the second piston and the gas
and fluid are not separated, leading to aeration. In these cases,
the shock can be run with the shaft-end down only.
All mono-tube gas shocks use a high gas
pressure which creates some problems for the race car. First,
there's a false spring rate that causes problems. An example:
When shock has 150 pounds of pressure at ride height, the pressure
change is small when compressed or extended. When a spring with
a 150-pound rate is compressed 3 inches from the ride height,
the pressure resistance will increase by 450 pounds. What this
means is that the 150 pounds of pressure in the high-pressure
gas shock is a false spring, because it doesn't increase 150
pounds per inch as would a normal spring.
Additional, this gas pressure raises the
center of gravity of the car while it is cornering. Here's what
happens as you car goes through a corner: the outside of the
car has 300 pounds of additional fixed-pressure resistance preventing
it form compressing the spring as far as normal. The result is
that the outside of the car goes down less and the inside of
the car is raised higher, creating an unbalanced center of gravity.
The lighter the race car, the more dramatic the change in the
center of gravity will be from the high gas pressure.
The High gas pressure thus raises ride
height and also makes scaling the race car difficult due to the
gas pressure acting as a false spring. If it is this difficult
to scale you car, imagine what difficulties might occur to your
car on the track.
Q: Okay,
that explains high gas pressure. Now explain low gas pressure
and its advantage or disadvantages.
A: Low gas-pressure shocks are twin-tube design, which
incorporates an inner cylinder inside the shock body. The piston
functions in the inner cylinder, thus preventing dents and dings
from hampering shock performance. This design uses a gas cell
located in the reservoir area of the shock. The gas cell appears
to be a relatively simple device that contracts and expands as
the shaft moves in and out of the shock.
Now for the unique function of this cell.
The gas which is used in the cell has very large molecules, much
larger than the molecules in the cell wall, which are no larger
than the molecules in air. The gas inside the cell attracts any
available air which can pass through the cell wall due to the
size differential. The air and gas molecules combine and for
a new molecule that's too big to pass back out of the cell. The
result is that any air which could possibly have been trapped
in the shock during assembly will collect into the cell, preventing
any possible aeration. This is a great problem because, however
hard you might try some minute of air is going to get into every
shock that is built.
The pressure is so low on the low gas-pressure
shock that it does not show even a pound of resistance. Therefore,
it doesn't change the center of gravity or ride height, nor create
problems while scaling the car.
Q: Which gas-pressure system
is used by Pro-Shocks?
A: The low gas-pressure system is used by Pro-Shocks,
because it offers all advantages without experiencing any of
the disadvantages found in the high gas-pressure system.
Q: Do
the two types of gas-pressure shock use the same valving system?
A: No, the high gas-pressure shocks use the blow-off
plate system instead of the more sophisticated coil-spring system
due to compact length. The floating piston adds so much dead
length to the shock that it is imperative to use the shorter,
less desirable system. Even with the shorter blow-off plate system,
the compressed length is almost an inch longer.
Q: Explain why the Pro-Shock
coil-spring is better than the blow-off plate system.
A: First, we need to explain the blow-off plate system.
This is a six-stage system consisting of three stages for compression
control and three stages for rebound control. Both the compression-
and rebound- control stages are the same. Stage one involves
a low-speed bleed or a predetermined leak in the blow-off plate
valve. In stage two a blow-off plate or plates allow fluid to
flow to stage three, which is the high-speed jet. Now this sounds
simple enough, and it is. The problem is the acceleration ramp
is very linear. Sounds good, but it's not. A race car needs two
primary things from the shock. Number one is low-speed control
(0 to 10-12 inches) which controls body roll and weight transfer.
Number two is high-speed control (10-12 to 30 inches) which controls
the tires and wheel through bumps, holes and waves in the race
trace. So, where's the problem? A linear ramp is fixed, so when
you need more body-roll control it will also give you more high-speed
resistance, or vice versa. In almost all cases the shock needs
two different acceleration ramps, one for low-speed functions,
a second for high-speed functions. This blow-off plate system
always forces compromise when designing a valve code for a particular
application.
Now for the coil-spring system. Pro-Shocks
uses an 11-stage coil-spring system which incorporates four coil
springs, four low-speed bleeds and three high-speed jets to operate
this hi-tech valving system.
What's the big deal about coil springs? Lets look at a simple comparison between coil springs and blow-off plates. The common automotive oil pump, which incorporates a coil-spring design, has approximately 20 pounds of pressure at 600-800 rpm, yet when you increase the rpm to 6000 the pressure will only increase to approximately 50 pounds of pressure. If we used a blow-off plate system, which is an easier and cheaper method, the 20 pounds of pressure would increase to several hundred pounds of pressure, a disaster for the engine. The beauty of our system is that we can pick the desirable low-speed ramp and the desirable high-speed ramp without compromise. This system is complex, making it impossible for the user to revalve. Simple return the shock to Pro-Shocks for revalving or rebuilding.
Q: How does Pro-Shocks write
a valve code to determine the desired acceleration ramps?
A: The valve code is a combination of valving components
it takes to create the desired low-speed and high-speed ramps.
We look at three key elements in determining codes: the race
track, the shock dyno and previous experience. This starting
point is generally very good because of the highly experienced
Pro-Shocks staff.
We know you can't race a dyno, so we spend
a lot of time at race tracks working with new products and concepts.
We bring our findings back to the dyno to simply look at what's
good and what's bad. From these findings we can determine which
acceleration ramps and valve codes will make the best new products.
Q: Can the low gas-pressure cell Pro-Shock be run upside down?
A: Yes, with the gas cell shock, you can run the shock in any direction, including horizontal.
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