kostas, just try it and if it is to restrictive, if the engine overheats or is weak you can remove the baffle and open up the outlet a bit to "derestrict" the muffler. I run the 91 fx with these mods even though I have the mid section in place and it made my engine a whole lot quicker to spool up my prop.(wasn`t to impressed with the performance in stock form) have no tachreadings before and after, but it certainly has more power now and no issues. trottles fine, runs great and never a deadstick as long as there is fuel in the tank