any straight through pipe that has a baffle and no fiberglass packing will be loud. You could just hack the mufflers off the stock head pipes and insert a small baffle.
but WHY do you want an unnecessarily loud exhaust? other than being annoying to everyone else and eventually yourself, they usually sound awful, and make less power. I'd personally stick to a system that has a nice muffler that will be louder than stock, actually sound good, and make better power.