Aftermarket air intake or cold air system, IHRA

IHRA answers this part for 24 of its classes. 4 of those answers permit the part outright and 13 permit it with stated conditions, leaving 7 that do not. 3 of the ones that do not are classes we read as open rather than as refusing it. 7 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

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 3 classes

On a closed list an unlisted modification is not permitted. · A.2.2, J.1

Not permitted, not listed in the rules 1 class

The pipes joining the turbo to the existing intake travel with the turbo under the reading of what DD.7 presupposes. An aftermarket air intake or cold air system beyond them is not in DD.7, and the DD preamble says what is not listed is not legal. · DD.7

Drag, Turbo No Nitrous

Legal, with conditions 6 classes

The ducting between the flame arrester and the throttle body may be modified or aftermarket, or only as far as the airflow sensor where one is fitted, and nothing downstream of the sensor may change. No cold air system is named, so the allowance stops at that ducting.

Runabout Lites · AA.3.1
Four-Stroke Ski Lites · N.3.1
Runabout GP2 · Y.3.1
Runabout GP3 · Z.4.1
Ski GP2 · L.3.1
Ski Limited · P.1, N.3.1

Legal, with conditions 2 classes

Where no airflow sensor is fitted, the ducting between the flame arrester and the throttle body may be modified. The clause names no aftermarket ducting, gives nothing for an engine with a sensor and names no cold air system.

Ski 1100 Modified · R.3.1
Ski 1500 Modified · Q.3.1