Originally Posted by Westvseast42
i was thinking of just cutting out the old muffler and clamping on an new muffler on my focus any thoughts on that..and will this void my warrenty
You can certainly do that. I know there are a few others who have done the same.
It will not void your warranty unless
they can prove it somehow caused a problem that you wanted fixed (see Magnuson-Moss Warranty Act).
Now, a dealer can refuse to work on your car if they want to if they find aftermarket parts, but most dealers are pretty easy going about the fairly minor stuff like exhaust, intake, etc.
Btw, nicely done to the Focus Fanatics mods for giving the GDI it's own performance sub-forum and moving our stuff to it!