FMF years 
what where doing when they designed their pipe? 

It is obvious that FMF did not spend much time developing their pipes back then.  They did not have to make much of an improvement to have a better pipe than the stock pipe.  They did not have or use a dyno for developing their pipes back then.   FMF did not get a dyno until around 1995.  They just used some pipe design software, built the test pipe, ran it up and down the alley behind the shop as a test, and then put an advertisement in the magazines.  If enough guys placed orders then they would make the tooling to start stamping pipes.  Once tooling is made for a particular design, most pipe builders are reluctant to make any major design changes because they seldom make enough pipes to ware out the stamping dies.  It is fairly easy to add or take away an inch to the length of each section of a stamping die to add a few inches to the over tuned length of the pipe.