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Class Legality

IHRA · Engine

Cylinder head work (4-stroke), IHRA

IHRA answers this part for 24 of its classes. 3 of those answers permit the part outright and 3 permit it with stated conditions, leaving 18 that do not. 3 of the ones that do not are classes we read as open rather than as refusing it. 13 are inferred from how the class is written rather than quoted from a rule naming this part.

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.

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

Original casting required for 1101cc+. Valve count must not change. · K.2.6

OEM part required 1 class

Original casting matching the engine block must be used. · X.2.6

Not permitted, not listed in the rules 1 class

P.2.2 frees the cylinder head on two-stroke entries only, and a four-stroke entry takes the Four Stroke Ski Lites rules with no exception, which list no head work beyond a one-bank repair that brings no performance gain. · P.1, N.2.1, P.2.2, J.1

Legal, with conditions 1 class

Bead blast chambers only with valves seated. Ports must NOT be bead blasted or abrasively cleaned. · W.2.2

Legal, with conditions 1 class

On the Kawasaki 750SX, 750SXI, 750SXI Pro and SXR800 drop-down domes are not allowed and O-ring head sealing with no head gasket is permitted, with a minimum dome of 28cc. · M.6.1.1

Legal, with conditions 1 class

Model-dependent. Two-stroke entries: Aftermarket permitted. V.2.7 Four-stroke entries: Original casting required; runners, chamber, valve placement modifiable. · V.4.8

Legal 1 class

Two-stroke entries: Aftermarket permitted. · BB.3.5

No rule, this is an open class 2 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.

No rule, this is an open class 1 class

No restriction in section CC, and CC.1 permits any modification it does not restrict.

Cylinder head work (4-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 · four stroke · legal in 6 of 24 answered, 3 with conditions

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BaddJet Class Legality