ive got a 3" magnex system on mine at the moment its 3" bore and 3" tip im pritty handy with a welder but am i right in thinking that the 4inch backbox compaired with the 3inch one would have diffrent size pipe/more or less baffles in it? or could i just cut the tip off and weld a new one on? because surely the tip doesnt make that much diffrence?