UIM · Exhaust

Aftermarket waterbox

Where the chamber is legal, the waterbox usually is not.

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This is one body's answer, not the sport's. You are bound by whichever body sanctions the event you enter, and where both govern you, you are held to the stricter of the two. The differences are set out in the rulebook comparison.

GP2 in both divisions is the trap: chamber yes, waterbox no. Split the SKUs.

Where it stands, class by class

19 classes, grouped by the answer rather than listed one by one, because an answer that holds for a class usually holds for every class that borrows its rules. 5 of them publish no component rules of their own and are marked below; for those, the link to the parent class is read from the categories table rather than stated in the rulebook.

No rule, this is an open class Our reading, not a rule we can quote at you. This class carries no stock clause at all, so anything unlisted appears to be open. The rulebook does not say so in terms.

Not legal 3 classes

Entire exhaust system of origin.

• Ski Division GP3 · 501.02
• Ski Juniors GP3.2 · 302.01 · borrows another class
• Ski Juniors GP3.3 · 302.01 · borrows another class

Not legal 1 class

Entire two-stroke exhaust of origin.

• Runabout GP3 · 502.02

OEM part required 1 class

OEM waterbox must be used and may not be modified. · 502.03.03-07

• Runabout GP2

OEM part required 1 class

THE OEM WATERBOX MUST BE USED AND MAY NOT BE MODIFIED, even though the chamber may be aftermarket. · 501.03.03.07

• Ski Division GP2

Governed by the parent class 8 classes

No component rules are published for this class and no single parent class is named, so this part cannot be answered for it. That is an absence in the rulebook, not a permission.

• Endurance · 317.03
• Freestyle Amateur · 312
• Freestyle Free · 312
• Jet Raid · 317.01
• Offshore · 317.02
• Parallel Slalom · 313
• Ski Future Electric (SFE) · 302.01
• UIM Hydro-Fly · 900

No rule, this is an open class 5 classes

No article.

• Ski Division GP1 · 501.04
• Runabout GP1 · 502.04
• Runabout Veterans GP1 · 302.01.05 · borrows another class
• Ski Ladies GP1 · 314 · borrows another class
• Ski Veterans GP1 · 302.01.05 · borrows another class

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Aftermarket waterbox: if the rule your class applies reads differently to you, or the rulebook has changed since this was read, ask. We answer with the section we read it from, or that we have not read it. Ask a rules question.

Every UIM class · where the rulebooks differ · signed checks on parts the shop sells.