looking to get a pipe for my 91fx,i see tower has the macs one piece muffler in stock,anybody have this and is there any differance over the stock besides weight,performance wise

Tuned pipes suck for 3D. The stock muffler or a beer bottle pipe are much better. The macs one piece muffler is somewhere in-between. I have a macs one-piece muffler on my 55AX and 160FX and it's good. It did make the midrange a little burbley but not bad. The high end got a little boost. The big benefit of the one-piece muffler is the weight savings (2.2oz on the 55AX and 6.2 oz. on the 160FX) over the stock muffler.

all the reasearch i did on the macs one piece they say it saves weight and will increase mid and top end,and they are not a tuned pipe but a muffler,i got one today on my way home and will put it on and try it,might need to readjust my needles with it on there right

I didn't say the one-piece is a tuned pipe but it is. It's not tuned only for top end though like a regular pipe is.