IHRA answers this part for 24 of its classes. 2 of those answers are permissions, with or without limits attached, and 22 are not. 22 are inferred from how the class is written rather than quoted from a rule naming this part.
This is one body's answer, not the sport's. You are bound
by whichever body sanctions the event you enter, and where both govern you,
you are held to the stricter of the two. The differences are set out in
the rulebook comparison.
Where it stands, class by class
24 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.
Not permitted, not listed in the rules 19 classes
On a closed list an unlisted modification is not permitted. · A.2.2, J.1
Aftermarket boost sensor: 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.