cbr f3 stock muffler cut in half cause its huge i say hug
..plus im broke so i cant buy a new one

 

Yes you can.

From this;


To this;


You're gonna encounter a couple of baffle plates that hold the inner tubes ( three if I remember) that you'll need to remove. I used a long cold chisel to cut around the outer edges. Once all the cutting is done just get some vice grips and rip those baffles and tubes out. I made my own perforated tube and used muffler packing but you can just pop rivet back on the end cap that you've cleaned up to fit back onto the muffler. It was a bit loud for me so I went with the packed option. With the perforated tube though you'll need to make some brackets and an end cap to hold it into (so it doesn't blow out) the original larger end cap. Good luck.