blitz nur spec r on a classic always sounded the dogs....i had an aps 3.5" system on my car a while back, thought it sounded really good.....if u want something really loud the team ice 1 from RCM would be good, or get 1 custom made, my mate just got 1 made for his P1, 4" from the turbo straight back, no silencers and it has a screamer pipe as well, it is loud as f*ck.....