Did you get a straight through muffler? It should sound much deeper if so. That should have been all you needed. My NA 300zx I had was louder than my 300ZXTT with just dual straight through magnaflow mufflers on the NA. I have 3" pipes with SZ downpipes and no cats on my TTZ and it's a little more quiet than the NA was. I'm betting you just got a muffler that mutes the exhaust too much.