Class rules

What is legal in UIM Ski GP3, and what the rulebook does not say

GP3 is the strictest exhaust rule in the UIM Ski Division and one of the plainest closed lists in the sport. The harder half is what the class leaves unstated, including a power ceiling with no stated way to measure it.

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The exhaust must remain entirely of origin

Article 501.02.03.03 requires the system as delivered by the manufacturer. There is no stinger allowance, no insert, no waterbox substitution and no through-hull change; the flap may not even be removed. Our data records this as the strictest exhaust rule in the UIM Ski Division, and it is stricter than the equivalent stock class rule in the American rulebooks, which at least permit an insert.

Nothing inside the engine may be touched

Article 501.02.03.02 refuses internal modification of any kind and names the methods: grinding, surfacing, polishing, machining and shot peening. Full porting is therefore out, an aftermarket head has no allowance, and the intake manifold has no article at all. What the class does permit at the top end is narrow and specific, which is the pattern throughout.

The carburettor list is five items long

Article 501.02.04.01 permits replaceable type jets, needle valves and needle valve springs, removal of the choke, and an aftermarket primer. It then says no other carburettor modifications, which removes the usual argument about what silence implies. Fuel injection has no allowance in this class, so an injection conversion is not a grey area here.

The two things the rulebook leaves genuinely open

The class states a maximum original engine power of 85 horsepower and never says how that figure is measured or verified, which makes it a ceiling nobody can check at the ramp. Separately, no reed valve article exists for GP3 at all. Under the closed list that reads as aftermarket reeds being illegal here while they are expressly legal one class up, and the rulebook never states the refusal in terms. We record both as uncertainties rather than answering them, because answering them would mean inventing the sentence the document is missing.

What we cannot tell you, and why we are saying so

This site has never checked a single product against a UIM class document. Every signed legality record here is against the American bodies, so we can tell you what the GP3 rulebook says and we cannot tell you whether anything in our catalogue passes it. That is why no parts are linked from this page. A shop that answered a UIM question with an American check would be giving you a confident answer to a different question, and the difference only shows up at inspection.

The numbers that decide eligibility before any part does

A two stroke atmospheric ceiling on displacement, a minimum dry weight of 135 kilograms, a sound limit of 86 decibels taken at 24 metres, a minimum rider age of 15, and at least 75 degrees of handle pole movement with the pole mounted ahead of the engine compartment. Homologation runs on 50 specimens with a conformity certificate. No model list is published, so eligibility is argued from those figures rather than read off a roster.

Before you act on this. Read from the 2026 rulebook as extracted into this site's data, and not checked by anybody who has raced the class. No product on this site has been verified against any UIM class document. Two of the answers above are recorded as open questions in the rulebook itself rather than as findings.

Symptoms this addresses: Racing UIM rather than a domestic series · Not sure whether aftermarket reeds are legal in GP3 · Told the exhaust must be entirely original · Need to know what a closed list means for parts nobody mentions. All symptoms.