The XJ-S is a heavy
beast. Let's face it, it's a luxury car, not a performer. The best
way to aggravate the Corvettes would be to pull about 800 pounds out
of this car. If you can do without the electric windows, electric
door locks, stereo system, 5 mph bumpers (see below), air
conditioning, back seat, spare tire, carpeting, sound insulation,
etc., etc., then go for it.
Light Weight Components
Another popular way to reduce weight is to replace components with
lighter versions. Chad
Bolles has replaced the radiator with an aluminum model, the
bonnet with a fiberglass one, the A/C compressor with a smaller
model, and other mods. Effective but expensive.
When making weight reduction modifications, bear in mind that such
mods will affect acceleration in the non-wheelspin realm by the
proportion of total weight of the car; removal of 200 pounds will
improve acceleration by 5% in a 4000-lb car. In conditions where the
wheels spin, weight reduction in the front of the car will help
slightly, weight reduction in the rear will hurt slightly. Weight
reduction has almost no effect on top speed (other than how long it
takes to get there). Weight reduction has a similar effect on
maneuverability as installing bigger tires; it may be negligible if
the present tires are adequate. Although it might feel different (and
that alone may justify the modification), the actual timed
performance may be insignificantly changed.
Spring Changes
Also bear in mind that the springs, shocks and other components
are designed for a 4000-lb car. If the weight reduction is
significant, the car will effectively be sprung more stiffly and will
ride higher. If the stock springs are cut shorter to bring the ride
back down, it will increase the stiffness even more. All of this may
be considered desirable in a car as soft as the XJ-S.
Weight Balance
Weight reduction from points high on the car is preferable, since
it will lower the center of gravity and make the car lean less in
corners. It is even beneficial to relocate components lower on the
car.
Weight reduction at the extreme ends of the car is also
preferable, because it reduces the moment of inertia of the car. In
other words, it reduces the car's tendency to resist beginning to
turn when going straight, and its tendency to keep turning when
beginning to straighten out. It is beneficial to relocate components
from the ends of the car to more centralized locations.
If weight is removed entirely from one end, it can change the
balance of the car. Since the XJ-S is obviously nose-heavy, it would
be helpful to either remove weight from the nose or relocate
components to the rear of the car.
Weight reduction on rotating parts, such as engine/drivetrain
moving parts, wheels and tires, brake rotors, etc., can have a much
greater effect on performance than general weight reduction
throughout the car.
On to Body
Modifications