I have a ’73 Duster that I compete in Pro ET with at my local NHRA track.  The car currently has a roll bar in it.  The car has a back-half installed, but the firewall, floor, and body are all stock.  This offseason I plan to build a new engine that should put my car into the low 6 second range in the eighth mile.  Will I need to install a complete roll cage?

Answer:

If your car will be running quicker than 6.40 in the eighth mile or 10.00 in the quarter mile you will need an NHRA certified roll cage even though you have an unaltered firewall, floor, and body.  Between 10.00 (6.40) and 10.99 (6.99) cars with your configuration are only required to have a roll bar so long as it is not a convertible.  Cars with an altered firewall, floor, or body running 10.99 (6.99) or quicker or faster than 135 mph must have a complete roll cage.