17.2 of the prepared rules
B. Chassis, frame, or subframe may be reinforced, provided components
and attachments are not relocated except where specifically
permitted. Reinforcing does not authorize the use of belly
pans forward of the firewall, or aft of the front edge of the rear
wheel opening. It is permitted to have jack points recessed into
the rocker panels, or to have one tube per side extending downward
through the bottom of the door, provided they do not
extend beyond the overall width of the car or in an unsafe or
dangerous manner. No part of the bodywork or chassis, to the
rear of the front wheel opening, shall touch the ground when
both tires on the same side of the car are deflated.
C. The chassis, frame, or subframe may be notched or cut and
brackets may be added for the purpose of attaching alternate
suspension or drivetrain components, except that the firewall may
not be modified for engine block or cylinder head clearance.
Holes may be cut to provide clearance for authorized suspension
and drivetrain components, through their entire range of travel.
Additional structure may be added in order to attach allowed
components to the chassis.
D. Replacement of any chassis component (e.g. subframe) in its
entirety by one of alternate construction, unless specifically
permitted, shall result in the vehicle being “in excess” of these
rules and weight penalties and/or competitive adjustments may
apply.
17.11 OTHER
A. Vehicles prepared in excess of Solo allowances and prepared up
to either the current GTCS or PCS are permitted to compete in
their respective Prepared classes. Section 17.8.B.7 minimum
track requirements apply. Minimum weight will be 110% of the
Solo minimum weight from Appendix A plus any Solo weight penalties
(wheel size penalties, etc.). Vehicles taking advantage of this
allowance may use Solo or GTCS/PCS allowances in whole, in part
or in combination. Cars which are not listed in the GTCS or PCS
may not use this allowance, and are limited to the modifications
allowed in Section 17. For those cars which have been de-listed
from the current year GTCS/PCS, upon member request the
appropriate specifications will be developed and added to Appendix
A. An exception to the GTCS will be that open cars are
permitted, provided they comply with all provisions of Section
17 pertaining specifically to open cars.
Prepared Class X
XP vehicles must conform to the rules in Section 17 except as noted
herein. This class is for almost any production car using almost any automotive
drivetrain. Any vehicle meeting the requirements of 17.A.2, listed
in another Prepared class in Appendix A, specifically listed in CP, DP, EP, FP
or GP that is not required to run at 17.11.A specified weights, or listed
below is eligible for XP. 17.11.A does not apply. “In-excess” cars are not
eligible for XP.
8. OTHER
Vehicles exceeding these rules and prepared to the GCR/GTCS or
GCR/PCS are not eligible for this class.
You can not have a tube frame car. The original frame and structure must remain. You can notch it, ad brackets to it, reinforce it, etc., but your suspension and body have to attach to factory structure. You cannot replace structural components in XP and simply take a weight penalty like you can in the other prepared classes.