IHRA answers this part for 29 of its classes. 29 of those answers are permissions, with or without limits attached, and 0 are not.
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
29 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.
Legal, within limits 26 classes
Gauges may be modified or removed provided no hazard is created and any resulting hole is sealed. Section J permits modification and removal and never addresses adding an aftermarket instrument. · J.15
The one class with a data-logging rule of its own. Air fuel ratio, exhaust gas temperature and detonation sensors are permitted for data logging only, and W.1.3 bans transmitting anything off a moving craft except official transponders, broadcast video and pit radio. Mirrors and speakers may be modified or removed provided seals stay intact. · W.4.1, W.1.3, W.7.1
Aftermarket gauges and data logging: 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.