The OS FP series were not built to take a tuned pipe. They are just not ported to take one. You would be better of with a newer 46AX and would have heaps more power out of the box with out a pipe than you would ever get from the 35. You can look for a Macs pipe or other, but pipe for the smalles motors are getting a lot harder to get because of electric. Try one on the boat suppliers, They may have something.

Cheers