Not permitted, not listed in the rules 3 classes
On a closed list an unlisted modification is not permitted. · A.2.2, J.1
IHRA · Engine
Aftermarket cylinder head (2-stroke), IHRA
IHRA answers this part for 15 of its classes. 4 of those answers permit the part outright and 3 permit it with stated conditions, leaving 8 that do not. 4 of the ones that do not are classes we read as open rather than as refusing it. 8 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
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
On the Kawasaki X2 pre-2005, the X2 2005 to 2007 and the Yamaha WaveBlaster 701 drop-down domes are prohibited, with maximum compression 190 lb and minimum squish clearance 0.04 in. On the Sea-Doo HX drop-down domes are prohibited, with maximum compression 175 lb and minimum squish clearance 0.051 in. · U.2.4
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 2 classes
Two-stroke entries: Aftermarket permitted.
- Ski Limited · P.2.2
- Runabout Limited · BB.3.5
Legal 2 classes
The cylinder head may be modified or replaced with an aftermarket one, with no dome, squish or compression limit stated.
- X2 Vintage · T.2.6
- Ski Vintage · S.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 cylinder head (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 7 of 15 answered, 3 with conditions