If you're referring to your attached pix, that's a header, not a pipe. These are the old style header that we used to run with the older 120s and the first generation 140s - the FZ and the L engines. It connects to a long pipe by means of silicon tubing.
I guess you can use just the header part, but you have to deal with the following:-
1) It will be pretty messy with the oil residual
2) It will be really loud, like running a car with straight through pipe with no muffler
3) Even though, 4 stroke doesn't require a tuned pipe, a 4 cycle pipe do enhance performance
4) If you do not mount them correctly, say, soft mount them, they will break easily