[F-BIRD'88]

On every car I have track tested that had flowmaster mufflers, it ran a whole lot faster and quicker when the
flowmaster mufflers were removed. A straight thru style muffler always works better.
EG: Magnaflow or DynoMax. Quieter too.
You have the mufflers. Go to the track and prove it to yourself.

I have a custom hand built one off modified tri flow (turbo mufflers) of my own design on my car.
The car runs slightly faster and quicker with the mufflers installed compared to open exhaust.
The difference is very very small. A lot quieter than flowmaster/no restriction.
Or if there is any restriction the engine don't know it.

Do a control tested A-B-A or B-A- B on-off-on test of at least 6 passes with good traction.