Files with drg extension might also be found as part of Dyno2000 program. Car design format.
DRG file extension - Dyno2000 car design
What is drg file? How to open drg files?
File type specification:
The drg file extension was also used in old Dyno2000 program for its default car design format.
Dyno is a provider of car engine simulation software that reveals (otherwise invisible) pressure waves and mass flow in cylinders and engine passages.