Every Mopar V8 motor I've added collector extensions to at the races help them, BB, Hemi, and SB motors with automatic and even stick shift SS/A Hemi cars with 4.0 inch H pipe collectors extensions
Depending on the track conditions, weather, elevation and tuning can make a difference on which length will work the best that day at that track
Marking them with crayon or soap stone helps you find out where to cut them off at for that day and track, I know several NHRA class racers that have 6.0 inch, 12.0 inch, 18 inch and even 24 inch long collectors in their trailers and swap them as needed