Not permitted, not listed in the rules 5 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 answers this part for 14 of its classes. 5 of those answers are permissions, with or without limits attached, and 9 are not. 9 are inferred from how the class is written rather than quoted from a rule naming this part.
Where it stands, class by class
14 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.
Not permitted, not listed in the rules Our reading, not a rule we can quote at you. This class requires the craft to stay stock except where the rules allow otherwise, and this part is not on the list.
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.
Legal, within limits 1 class
Swappable within the same manufacturer. Aftermarket sleeves allowed but port sizes must match the OEM sleeve. · O.2.7
Legal, within limits 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, within limits 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, within limits 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 · signed checks on parts the shop sells.
Engine · two stroke · legal outright in 5 of 14