"But what about blowers like the 14-71?"

The 14-71 as used in Top Fuel and Funny Car is a purpose-built aftermarket design. Here are the spec limits:
Case length max. 22 1/4"
Case width max. 11 1/4"
Rotor length max. 19"
Rotor diameter max. 5.840" including fixed stripping
The case must be one piece with removeable front and rear bearing end plates. Rotor must be contained within one-piece case. Inlet/outlet cavity restricted to max. one inch, measuring from the face of the bearing plate to the back of the cavity.