Okay so i had a little fun today with my new snake pipe, i matched the exhaust header to the exhaust port.
With most pipes the header is round where it bolts onto the cylinder, but the exhaust port is rectanglular. This causes alot of restrictions! So you need to match these ports to free up the flow of the burnt gases out of the cylinder.
BEFORE
AFTER
This will only cost you $15.40 and some spare time.
Here is what u will need: Drill/die grinder/dremel, Grinding stones, small file set.

Those are from supercheap auto (its closer than bunnings for me).
So get a rectangular exhaust gasket and trace around the edges with a permanent marker on your exhaust header, this will be your guide while your grinding/filing.
Put it in a vice and start grinding, make sure you dont go too far though!
Once you have taken the bulk of the metal start filing, use the full round file to get right into the corners, now use the flat file to get the edges straight.
It is pretty much common sense when your doing it, nothing too hard.
Dont forget to trim your exhaust gasket so it doenst block the flow.
Regards,
Rob Wright.