5.1.2 Class limits are set as follows:
a. GTU (as applied to all GTU classes except Lightweight Superbike)
i. Up to 430cc two- or more-cylinder, two-stroke, unlimited origin
ii. Up to 550cc two- or more-cylinder, two-stroke, if frame is from a motorcycle manufactured for street use in North America
iii. Up to 550cc single-cylinder, two-stroke, unlimited origin
iv. Up to 675cc three-cylinder, four-stroke, liquid cooled
v. Up to 640cc four-cylinder, four-stroke, liquid cooled
vi. Up to 850cc two-cylinder, four-stroke four or more valves per cylinder, liquid cooled
vii. Up to 900cc three- or more-cylinder, four-stroke, air cooled
viii. Unlimited displacement air cooled two-cylinder, four-stroke two or three valves per cylinder
ix. Unlimited displacement single-cylinder, four-stroke, unlimited origin
x. Forced induction (e.g., turbo- or supercharging) is not allowed
xi. Exception: Ducati 899 and 959 are permitted to race in this class