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Class Legality

UIM · ski

Ski Division GP2

UIM 2026, 501.03. A closed-list class. The craft must stay stock except where the rules allow otherwise, so anything unlisted is not permitted.

  • 4Not legal
  • 7OEM part required
  • 6Not permitted, not listed in the rules
  • 1The rules do not say
  • 29Legal, with conditions
  • 22Legal

Read out of the published UIM rulebook on 2026-09-08, so confirm anything that decides a purchase. The full note is at the foot of the page.

Running the class

Displacement limit
750cc turbocharged, 850cc two-stroke atmospheric and 1620cc four-stroke atmospheric (501.03.01.01). The 2-stroke engine section permits the engine to be bored and requires the displacement not to exceed the class designation, so the figure is a ceiling on the engine as raced. The class also runs four-strokes, whose own section carries no boring allowance. 501.03.03.
Minimum weight
135 kg dry for a two-stroke, 165 kg dry for a four-stroke.

Read from the same class section as the part answers. The rider side of the sport, tiers, ages, licences and what gets inspected, is set out across the bodies at Racing.

Open questions on this class (4)

Places where the rulebook contradicts itself, or where a figure could not be settled. Nothing in this list is decided, and it sits here rather than in a footnote because it is what you would want before spending money.

  • The 750 cc turbo limit is not cross-confirmed against the 302.01 table.
  • The HSR-Benelli "limited to 10-14 psi" phrasing is odd for a limit - permitted band or maximum is unresolved.
  • No ballast article, so whether ballast may be used to reach the 135/165 kg minima is not stated.
  • No separate four-stroke exhaust rule was found (501.03.03.07 sits under the two-stroke engine article).

What the rules say (69 parts)

22 permitted outright, 29 permitted with stated conditions, 4 refused by a rule we can quote, 7 held to the original part by a rule we can quote, 6 refused by our reading of the class rather than by a quoted rule and 1 the rules do not settle. Grouped where the same rule gives the same answer, so two "Not legal" groups can sit side by side under different rules.

What each answer below means

Not legal
This comes off. The rules refuse it in this class.
OEM part required
This comes off. Only the part the manufacturer fitted is allowed here.
Not permitted, not listed in the rules
Treat it as coming off. The class requires the craft to stay stock except where the rules allow otherwise, and this part is not on the list, so this is our reading rather than a rule we can quote at you.
The rules do not say
Unanswered. The rules do not settle this, so ask the club before you rely on it.
Legal, with conditions
Keep it, but measure it: the rules permit this part only inside stated limits.
Legal
Keep it. The rules permit this part in this class.

Read the refusals as a list of work. Anything below marked Not legal, OEM part required, or Not permitted has to come off the machine, or go back to the standard part, before it races in this class.

Not legal1 part

Sensors and actuators must remain original; no aftermarket ECU allowance. 501.03.08

Not legal1 part

Homologated production craft only - 50 specimens, marketed, conformity certificate. 500.02.01

OEM part required1 part

Two-stroke: the OEM water box must be used unmodified even though the chamber may be aftermarket. Four-stroke: the engine article prints no exhaust allowance, so the original water box stays. 501.03.03.07, 501.03.04

OEM part required1 part

Camshaft and crankshaft must remain stock. 501.03.04

OEM part required1 part

The valves themselves must remain original. 501.03.04

OEM part required1 part

The hull may be repaired but not otherwise modified, and a repair may not alter the original configuration by more than 5 mm. 501.03-02, 501.02.02-02

Not permitted, not listed in the rules1 part

Ski GP2 lists atmospheric engines and turbocharged ones to 750 cc but no supercharged configuration, so there is no supercharger to rebuild. 501.03-02, 501.03.01-01

Legal, with conditions1 part

Manifold, head pipe, expansion chamber, gaskets and the chamber-to-waterbox hose may be modified or aftermarket. The OEM WATERBOX must be used unmodified, the exit opening size and position must be maintained, and no tuned portion may protrude outside the hull. 501.03.03.07

Legal, with conditions1 part

Permitted subject to SAE J30R9 high-pressure hose, A.N. threaded fittings or equivalent with non-removable crimped clamps, metal-type filters only on the high-pressure side, and a fuel pump that stops automatically when the engine shuts off. 501.03.05.03

Legal, with conditions1 part

Two-stroke: flame arresters meeting the USCG, SAE J-1928 Marine or UL-1111 Marine backfire standard must be fitted, aftermarket ones included, and the intake silencer may be removed. Four-stroke: equivalent aftermarket air filters or flame arresters available on the market. 501.03.05.05, 501.03.06.01

Legal, with conditions1 part

Aftermarket or modified electric fuel pumps not exceeding 4 psi, stopping automatically when the engine shuts off. Manually operated on/off pumps prohibited. 501.03.05

Legal, with conditions1 part

Two-stroke: a modified or aftermarket filler cap is allowed if no hazard results. Four-stroke: the four-stroke fuel article has no filler cap clause, so the original cap stays. 501.03.05.04, 501.03.06

Legal, with conditions1 part

Modified or aftermarket, not exceeding 5 cm x 15 cm, with a return line to the tank open at all times. 501.03.05

Legal, with conditions1 part

Must fit the OEM battery box and be securely fastened. GP2 additionally allows relocation of the battery, box or housing limited to the strict minimum needed to fit an aftermarket exhaust.

Legal, with conditions1 part

Cylinders may be machined to accept girdle-system cylinder heads. If OEM cylinders do not give displacement within 10% of the maximum allowable, an aftermarket cylinder SLEEVE may be used, keeping the same port sizes and specifications as the original OEM sleeve. 501.03.03.14

Legal, with conditions1 part

Must retain original port timing, compression ratio, dome profile, skirt length/shape and material type, and weigh within +/-25.00% of OEM. 501.03.03.01

Legal, with conditions1 part

Rebuild allowed. Stroke and rod length may NOT change. Bearings must keep original type and dimensions. Counterweights must resemble the original with no new holes or pockets. Total assembly weight within +/-5.00% of OEM. Non-ferrous counterweights, crank pins and connecting rods are prohibited. 501.03.03.02

Legal, with conditions1 part

Chamfering of NON-ORIGINAL cylinder ports up to 1.00 mm at a maximum 30 degree angle. 501.03-02, 501.02.03.04

Legal, with conditions1 part

Two-stroke: a replacement starter motor and bendix may be used. Four-stroke: no starter clause appears for four-strokes, so the original stays. 501.03.03.09

Legal, with conditions1 part

Turbocharged permitted, capped at 750 cc. The only named boost figure in the whole rulebook is 10-14 psi for the HSR-Benelli S4 (501.03.04-09), and that phrasing is ambiguous.

Legal, with conditions1 part

Permitted for the HSR-Benelli S4 specifically - intercooler and lines may be replaced or aftermarket. 501.03.04-09

Legal, with conditions1 part

Permitted, subject to the limits UIM applies to every class, namely the sound ceiling, the hull repair tolerance, the fuel specification, and the intake grate, sponson and pump dimensions.

Legal, with conditions1 part

Modified or aftermarket. The complete pump and nozzle assembly may be no more than 50.00 mm longer than OEM, and a 1:1 drive ratio must be maintained. 501.03.09/.10

Legal, with conditions1 part

Modified or aftermarket provided a 1:1 drive ratio is maintained. TITANIUM driveshafts, impeller housings and stator vane assemblies are PROHIBITED. 501.03.09

Legal, with conditions1 part

Two-stroke: aftermarket nozzle-trim systems may be used. Four-stroke: no trim allowance appears, and no transmission component may be modified. 501.03.09.01, 501.03.10.02

Legal, with conditions1 part

Full-length type with at least one bar parallel to the drive shaft, all leading edges radiused, extending no more than 12.00 mm below the flat plane of the pump intake area. GP1 adds that the projecting member must be filed so as not to create a hazard.

Legal, with conditions1 part

Max 153 cm each, 210 cm total, via the Kawasaki SXR1500 derogation. 501.03.02

Legal, with conditions1 part

The pole and its mounting bracket may be modified or aftermarket if they work as originally designed, the attaching point may be reinforced and the spring changed, and the pole must sit in front of the engine compartment with at least 75 degrees of movement. 501.03.01.06, 501.03.02, 501.02.02.10

Legal, with conditions1 part

Handlebar, throttle, throttle cable and grips may be modified or aftermarket, with padding at the mounting bracket or on the crossbar if one is fitted. 501.03.02, 501.02.02.09

Legal, with conditions1 part

The clause first says original switches must be used and then that aftermarket switches and switch housings may be used; housings may be aftermarket and switch positions changed under either reading. 501.03.02, 501.02.02.09

Legal, with conditions1 part

Replacement bumpers allowed. A soft flexible water-spray deflector may attach to the hull sides or bond flange, not exceeding the perimeter of the original bumpers or the external hull edge measured with a plumb line. SAFETY BUMPERS ARE COMPULSORY in both GP1 classes.

Legal, with conditions1 part

All cooling system valves must be of FIXED OR AUTOMATIC type - thermostats, pressure regulators, solenoids. Manually controlled devices that alter cooling water flow while under way are prohibited in every class, as are electronic water injection systems unless of origin.

Legal1 part

Carburetors may be modified or aftermarket, so jets, needle valves and their springs may be changed, provided the carburetor does not vent or spill fuel, has no more venturis than cylinders and is not a slide type. 501.03.05.01

Legal1 part

Two-stroke: the GP3 allowance for the ducting, support and adapter between flame arrester and carburettor carries over. Four-stroke: ducting from the flame arrester to the throttle body, intake manifold inlet or compressor may be modified or aftermarket. 501.03-02, 501.02.04.01, 501.03.06.02

Legal1 part

CDI unit may be modified or aftermarket; RPM limiter bypassed or eliminated; ignition timing may be changed. OEM charging system required. 501.03.07.01

Legal1 part

Two-stroke cylinder head AND GASKET may be modified or aftermarket. 501.03.03

Legal1 part

Diameter constraint lifted for two-stroke; impeller, housing, stator, plate and shoe all modifiable. 501.03.09

Legal1 part

Aftermarket hoods may be used and OEM hoods may be modified. 501.03.02

Legal1 part

Padding and mat kits may be added and custom painting is allowed. Metal components above the bond flange may be polished, shot peened or painted.

Legal1 part

The original bilge pump may be modified, disconnected or removed and aftermarket bilge draining systems are allowed if no hazard is created. 501.03-02, 501.02.02.12

UIM 2026, 501.03, read from the rulebook on 2026-09-08. Read the rule yourself. Every UIM class · where the rulebooks differ · how this site reads a rulebook.

This is one class. Every part below also has a page of its own showing where it stands across every class this body runs, and legality by part is the index of them.

Cite this page

“Ski Division GP2, UIM class rules”, BaddJet archive, https://baddjetarchive.com/legality/uim/ski-gp2/

Add the date you read it.

69 parts read · 22 permitted, 29 with conditions · 2026 rulebook

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