[ItBites]

Bob is mostly right on for NHRA full-on racer rules.

Run-what-ya-brung nights have the following modifications for street cars:

Harnesses are not required, at least to 13.00 (maybe 12.00).

Helmets are not required in hartop cars down to 14.00.

Other than that, in general:
I can also add that at least one forward facing light is also required, as well as "long" (they must protrude one stud diameter past the wheel nut) wheel studs if running slicks.

In a hardtop, at 12.00 and lower you only need a 4-point bar, not a full cage. at 11.00 and below, you need to step up to a cage.

Additionally, below 11.00, you need to get rid of the IRS and go to a live axle (unless you're running SS).