I actually concur with celicaizpower
Changing the exhaust won't benefit much on the speed.
There is , but only a slight increase on the horsepower and top end speed.
To be honest, a 250 cc changing the exhaust is merely cosmetics and sound emphasizing .
A parallel inline engine would sound like a thumping bass.
Just get a cheap one roughly below RM1k that would suffice.
The other 3K can be invested in other materials such as the paint , tyres , sliders , fenders and so on.

This post has been edited by AccelTech: Nov 20 2014, 11:13 AM