v6mustang

I recently bought a sct x4 tuner for my 2015 mustang v6 and I bought it to bypass the government chip but when I went to try it out after I tuned it Its like it didn't do anything because I was still stuck at 123 mph

If anyone has info on companies that could be making a cat back for the V6 let me know. I know MagnaFlow has made one or two but I might be waiting even longer since my car is a convertible.