I have an old Triumph motorcycle 955i that im customising. I want to change the exhaust and use a second hand yoshimura cheap one
Is that possible? Or the exhaust needs to handle different pressure or other variable?
If that second hand exhaust was designed for an engine of similar capacity and type, but not smaller, then it should be fine.
If you don't have a smooth transition from one pipe diameter to the other, then you can cause weird problems due to pressure characteristics created by the abrupt change in diameter.
The other issue is the fixing points, but that is something to deal with when you look at how it fits.