2 inches in diameter. This can be followed by a length of
2
inch pipe a couple of feet long.
also listed. More ratios will be added to the list as they
become available.
GEAR RATIOS
TRANSMISSION,
FINAL DRIVE,
CLUTCH AND FLYWHEEL
The 1500 5-speed transmission is allowed on both the
G- and F-production
XI19
cars. However, a great number
of changes were made to the cars when the 5-speed was
incorporated. This makes installing a 5-speed in an earlier
car rather difficult. Regardless of whether the 5-speed or
4-speed transmission is used, the gear ratios, including the
final drive ratio, must be optimized for racing. Some form
of locked or limited-slip differential will improve corner-
ing speeds in general. The clutch and flywheel must be
modified to handle high-speed down-shifting as well as
the extra power and abuse of the race car application.
Changes Associated With
The 5-Speed Gearbox
There are numerous changes, besides the addition of a
5th gear, associated with the 1500 5-speed gearbox.
The gearbox has been lengthened with a cover over
the extra gear set. This requires an indentation in the
frame and one in the left rear suspension control arm for
clearance.
The universal joints have been changed to identical
constant velocity joints on each end of each half shaft.
These bolt onto flanges, so the two half shafts and their
C-V joints can be removed by taking out the 24 bolts
(6
per C-V joint). This change requires a completely new
final drive setup with new stub axles, bearings and seals.
Also, the stub axles in the wheels have been changed and
larger wheel bearings are incorporated.
The flywheel and clutch have been changed in order
to use a larger diameter clutch disc. The ring gear on the
flywheel has a larger pitch diameter, and a new starter is
incorporated in a different location than on the earlier
cars.
Inside the gearbox, reverse gear has been relocated
and the shift mechanism has been changed to select the
5th speed.
From the above list of changes, it can readily be seen
that adding the 5th gear to the 4-speed car is not a simple
job. In fact, it is probably more trouble than it is worth
for G-production racing. There are 5-speed conversions
(such as Colotti) available from Italy, but these are not
legal for G-production racing, since the rules specify the
same transmission as is homologated for the F-production
car.
Close Ratio Gears
Following is a list of available close ratios for the 4-speed
and for the 5-speed transmission. Final drive ratios are
FINAL DRIVE RATIOS
Bearing Sleeves
For racing, the bearing sleeves on the driven gears must
be modified to allow more oil to flow through the bear-
ing. If this is not done, the gears have a tendency to sieze
onto the bearing sleeves. This typically results in the
transmission effectively locking in two gears at once. This
modification is easily accomplished by cutting spiral
grooves in the bearing surface with an abrasive disc.
Modifying Transmission Bearing Sleeves For Oil
Flow
Differential
The differential should be modified to prevent loss of
traction during hard cornering. Either a limited-slip can
be installed, or the differential can be locked completely,
such as by welding.
Flywheel and Clutch
The flywheel and the clutch must be modified so that
downshifting at high speed will not damage the clutch
pressure plate. If this is not done, the reversed loads when
the engine is used for braking (either intentionally or in-
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