OEM part required 1 class
N.2.5 allows no modification to the water box, which stays as supplied while aftermarket piping runs from it to the outlet pipe. · N.2.5
IHRA · Exhaust
Aftermarket or modified waterbox, IHRA
IHRA answers this part for 29 of its classes. 1 of those answers permit the part outright and 8 permit it with stated conditions, leaving 20 that do not. 4 of the ones that do not are classes we read as open rather than as refusing it. 17 are inferred from how the class is written rather than quoted from a rule naming this part.
This page is IHRA only, and the bodies do not agree. The same part under IJSBA and UIM. Which one applies to you is decided by whoever sanctions the race you enter.
Where it stands, class by class
29 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.
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.
- 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.
- 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.
OEM part required 1 class
O.2.5 keeps the whole exhaust system stock, water box included, with only a stinger-diameter insert allowed. · O.2.5
OEM part required 1 class
The water box stays OEM on either engine type: N.2.5 bars any change to it on a four-stroke entry, and P.2.1 frees the two-stroke exhaust only as far as the hose to the OEM water box. · N.2.5, P.2.1
Not permitted, not listed in the rules 13 classes
On a closed list an unlisted modification is not permitted. · A.2.2, J.1
Legal, with conditions 3 classes
Waterbox must be retained; aftermarket permitted with a through-hull exhaust pipe. STRAIGHT PIPES NOT PERMITTED.
- Drag, Yamaha Pro Stock · DD.1
- Drag, Yamaha Spec · DD.3
- Drag, Sea-Doo Spec · DD.4
Legal, with conditions 1 class
Must be retained; aftermarket with through-hull pipe. No straight pipes. · DD.2
Legal, with conditions 1 class
Model-dependent. The Kawasaki SXR800 may fit an aftermarket wet pipe exhaust system under M.6.1.4, and the water box, the muffler of a two-stroke wet exhaust, is read as part of that system. Every other Ski GP3 model may only repair its water box, keeping the original internal configuration. · M.4.3, M.6.1.4
Legal, with conditions 1 class
Part of the exhaust system, which "including the manifold, pipes, hoses, and mufflers, may be modified or replaced with aftermarket parts"; the exhaust exit may be relocated to the transom. Section K never keeps the water box OEM, as the restrictive classes do in terms. · K.2.5, K.3.5
Legal, with conditions 1 class
Part of the exhaust system, which may be modified or replaced ("including head pipes and mufflers", V.2.5; "manifold, connecting pipes, hoses, muffler(s), etc.", V.4.4). Through-hull exhaust may be aftermarket if it creates no hazard, no tuned portion may protrude beyond the hull, and the exit may relocate to the transom below the bond flange. · V.2.5, V.4.4
Legal, with conditions 1 class
Part of the exhaust system, which "including the manifold, connecting pipes, hoses, and mufflers, may be modified or replaced with aftermarket parts". Through-hull exhaust may be replaced if it creates no safety hazard, the tuned portion must not extend beyond the hull, and the exit may move to the transom below the bond flange. · X.2.5
Legal 1 class
Aftermarket exhaust systems are permitted, the water box with them, and straight pipes are allowed. · DD.5
No rule, this is an open class 3 classes
The class states only what it bans and calls itself run what you brung, against a section DD preamble that says anything unlisted is illegal.
- Drag, 2 Stroke Unlimited · DD.12
- Drag, Stand Up Unlimited · DD.10
- Drag, Unlimited · DD.6
No rule, this is an open class 1 class
No restriction in section CC, and CC.1 permits any modification it does not restrict.
- Freestyle · CC
Aftermarket or modified 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 IHRA class · where the rulebooks differ · checks on parts the shop sells · how this site reads a rulebook.
Exhaust · two and four stroke · legal in 9 of 29 answered, 8 with conditions