UIM · Exhaust

Aftermarket waterbox, UIM

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

This page is UIM only, and the bodies do not agree. The same part under IHRA and IJSBA. Which one applies to you is decided by whoever sanctions the race you enter.

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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. If you race more than one series, build to the stricter answer. The differences are set out in the rulebook comparison.

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

Where it stands, class by class

24 classes, grouped where the same rule gives the same answer rather than listed one by one, because an answer that holds for a class usually holds for every class that borrows its rules. 8 of them borrow another class’s rules and are marked below; for those, the link to the parent class is read from the categories table rather than stated in the rulebook. 8 publish no rule for this part and name no parent to borrow one from, and are grouped together at the end.

What each answer below means

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.

No rule, this is an open class

Probably keep it. The class carries no stock clause at all, so anything unlisted appears to be open. The rulebook does not say so in terms, and this is our reading rather than a permission anybody wrote down.

No rule published for this class

Unanswerable here. This class publishes no rule for the part and names no parent class to borrow one from, which is an absence in the rulebook and not a permission.

OEM part required 3 classes

The exhaust system must remain entirely of origin as delivered by the manufacturer, so the original water box is required under 501.02.03.03. · 501.02.03.03

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

OEM part required 2 classes

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.

• Runabout GP2 · 502.03.03-07, 502.03.04
• Ski Division GP2 · 501.03.03.07, 501.03.04

OEM part required 1 class

Two-stroke: the exhaust system must remain entirely of origin, so the original water box is required. Four-stroke: Runabout GP3 has no exhaust article, so the water box stays stock under the class's own stock clause. · 502.02-02, 502.02.03-03

• Runabout GP3

Not permitted, not listed in the rules 5 classes

The class is four-stroke only and prints no exhaust article, so the original water box stays fitted under its own stock clause.

• Runabout GP4 · 502.01-02
• Ski Division GP4 · 501.01-02
• Runabout Juniors GP4 · 502.01-02 · borrows another class
• Runabout Ladies GP4 · 502.01-02 · borrows another class
• Ski Juniors GP4 · 501.01-02 · borrows another class

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

No rule published for this 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

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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.

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