Most states do not require a vehicle 25 years of age or older to retain emission control systems or pass 'smog' tests.
This is true.
However, in the best of interests:
A. Federal Law
The federal tampering prohibition is contained in section 203(a)(3) of the Clean Air Act (Act), 42
U.S.C. 7522(a)(3). Section 203(a)(3)(A) of the Act prohibits any person from removing or rendering
inoperative any emission control device or element of design installed on or in a motor vehicle or motor
vehicle engine prior to its sale and delivery to an ultimate purchaser and prohibits any person from
knowingly removing or rendering inoperative any such device or element of design after such sale and
delivery, and the causing thereof.
Therefore, a pipe for 'testing' it is.
