OEM part required 1 class
Two-stroke entries: the exhaust system must remain stock, and an insert may reduce the inside diameter of the stinger. Four-stroke entries carry no expansion chamber. · Z.3.3
IHRA · Exhaust
Aftermarket expansion chamber / tuned pipe (2-stroke), IHRA
The highest-value two-stroke part and the one IHRA splits hardest by class.
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.
Ski Lites and Runabout GP3 two-stroke forbid it outright. Ski Limited permits it on the same machine. Never answer without naming the class.
Where it stands, class by class
15 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.
- 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
Must remain OEM. Stinger-diameter reducing insert allowed; cooling lines may be added to the insert. · O.2.5
Not permitted, not listed in the rules 1 class
Y.2.5 opens previously drilled manifolds if sealed, flange removal, removal of the resonator, sensor mounts and the external outlet, keeps the water box OEM, and names no expansion chamber; two-strokes may enter under Y.1, and under J.1 and A.2.2 an unlisted modification is not permitted. · Y.2.5
Not permitted, not listed in the rules 1 class
DD.7 states no engine type, so a two-stroke entry cannot be ruled out, and DD.7 does not list this part, so under the DD preamble it is not legal on either engine. · DD.7
Legal, with conditions 1 class
Model-dependent. On the Kawasaki X2 pre-2005, the X2 2005 to 2007 and the Yamaha WaveBlaster 701, WET-STYLE SYSTEMS ONLY, with dry-type systems and water-jacketed chambers prohibited and no tuned portion outside the hull. Electronic water injection is prohibited on all models. On the Sea-Doo HX the stock exhaust and water box must be unmodified, with no spray bars, stinger sprayers or water injectors, factory water routing and no bypass systems, and larger bolts or studs allowed. · U.2.3
Legal, with conditions 1 class
An aftermarket pipe enters Ski GP3 through the model clauses, not the exhaust rule: the Kawasaki SX-R 800 may run an aftermarket wet pipe (M.6.1.4), and a Yamaha SuperJet on the 701 cylinder may run a manufactured, designed and sold wet pipe that functions as one, a dry pipe converted being barred (M.6.2.1.2); on the 760 cylinder the exhaust must remain stock. Other machines and any dry pipe stay at M.4.1, stock pipe plus the reducer and fitting. · M.6.1.4, M.6.2.1.2
Legal, with conditions 1 class
Two-stroke entries: Manifold, head pipe, expansion chamber, gaskets, and hose to the OEM water box. Exit location and original opening size must be maintained. · P.2.1
Legal, with conditions 1 class
Model-dependent. On four-stroke entries removal of the plastic resonator is permitted (BB.2.6). On two-stroke entries the manifold, head pipe, expansion chamber, gaskets and the hose to the OEM water box may be aftermarket, the exhaust gas location may not be relocated, the original opening size must be kept, THE ORIGINAL WATER BOX IS REQUIRED AND UNMODIFIED, and no tuned portion may sit outside the hull. · BB.3.4
Legal, with conditions 1 class
Exit may relocate below the transom bond flange. No tuned components may protrude outside the hull. · T.2.5
Legal, with conditions 1 class
Manifold, head pipe, water box, expansion chamber, muffler. Exit may relocate to the transom but must not extend beyond the hull. · S.2.5
Legal, with conditions 1 class
No tuned portion may extend outside the hull. · CC.2.2
Legal, with conditions 1 class
Four-stroke (V.4.4): no tuned portion may protrude beyond the hull; exit may relocate to the transom below the bond flange. · V.2.5
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
What we corrected here, and when
- Runabout GP2. Corrected 2026-09-30: this cell repeated the through-hull outlet note.
- Runabout GP3. Corrected 2026-09-30: this cell read allowed with limits on a note about drilled four-stroke manifolds and a stinger insert, neither of which is an aftermarket chamber, so the row contradicted its own lead sentence.
- Ski GP3. Corrected 2026-09-30: this cell cited M.4.1 alone, which allows only a stinger reducer and a water fitting on the stock pipe, the same allowance Ski Lites carries under O.2.5, so the two classes read opposite verdicts from one rule.
Aftermarket expansion chamber / tuned pipe (2-stroke): 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 stroke · legal in 8 of 15 answered, all with conditions