What does upgrading a exhaust pipe on a RC NITRO Car to aluminum from plastic do? I have a exceed rc nitro forza 1/10th scale. I wanted to upgrade the exhuast pipe to aluminum. Will it make it faster? Louder? More protected? I also wanted to upgrade the shocks to metal since one of them broke from jumping hills?

Changing an exhaust pipe wouldn't make something faster. Also, it would depend on how the aluminum exhaust pipe was made as to whether or not it would make it louder. If you want it to be louder, you can play around and make different exhausts and see how leaving and/or shaping the metal can give it different sounds. Or if your buying, do research on the pipes before you buy them.
As for the shocks, I'm not sure.