Not permitted, not listed in the rules 4 classes
On a closed list an unlisted modification is not permitted. · A.2.2, J.1
IHRA · Engine
Aftermarket or swapped cylinder (2-stroke), IHRA
IHRA answers this part for 15 of its classes. 1 of those answers permit the part outright and 5 permit it with stated conditions, leaving 9 that do not. 4 of the ones that do not are classes we read as open rather than as refusing it. 9 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. Which one applies to you is decided by whoever sanctions the race you enter.
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
- 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.
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
Swappable within the same manufacturer. Aftermarket sleeves allowed but port sizes must match the OEM sleeve. · O.2.7
Legal, with conditions 1 class
Yamaha WaveBlaster may upgrade to 701 62T style cylinders; pre-1996 may update to 1996+ components; Yamaha 760 cylinders allowed subject to U.4.1 ignition restrictions. Cylinders may be machined for girdle-system heads. Limits: max overbore 1 mm. · U.2.1
Legal, with conditions 1 class
2-stroke cylinders interchangeable within the same manufacturer. May be bored to the class cc limit, which may exceed a 1 mm overbore. M.2.4 Yamaha SuperJet (2-stroke): 760 cylinder: allowed, aftermarket CDI box allowed, exhaust must remain stock. 701 cylinder: purpose-built wet pipe allowed (converting a dry pipe is NOT), CDI must remain OEM, timing may not be altered, head and base gasket OEM thickness, cylinders OEM bored max 1 mm over. · M.6.2.1.2
Legal, with conditions 1 class
Cylinders may be swapped between craft of the same manufacturer, and an aftermarket sleeve may hold the engine within 850 cc only if its ports match the original OEM sleeve, as P.2 adds nothing to O.2.7 for cylinders. · O.2.7
Legal, with conditions 1 class
Two-stroke entries: Interchangeable within the same manufacturer. Any cylinder or crankcase modification must be approved. · BB.3.5
Legal 1 class
Two-stroke entries: Port height and width changes and added cooling fittings permitted. · V.2.7
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 swapped cylinder (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.
Engine · two stroke · legal in 6 of 15 answered, 5 with conditions