I have an '03 SLE and was wondering what can I expect out of a 3" downpipe with manifold sound and power wise? I guess what I want is a little better sound and power wouldnt be bad?

With just the downpipe you might here a little deeper sound, power wise, very little. You will still need to do something with the manifolds to start feeling any difference. Each thing you do to the exhaust will deepen the tone a little more. High ratio rockers, PEMs or headers, 3" down pipe, free flow cat. Each of these will effect sound and performance to some extent. Think of it this way. The gases will move threw it as fast as the most restrictive point will let it.

Thanks for the response, I mean i'm not looking for crazy loud sound but I would like a nice deep sound sort of like the gxp gives off. I was thinking the downpipe with manifold and maybe new mufflers with tips? or just tips?

This is my set up. Keep in mind this is a total exhaust make over. 1.9:1 rockers, TOG headers with 1 5/8" primarys, 3" down pipe, 3" free flow cat, Flowmaster series 80 muffler.

for a n/a bonneville i would do ported manifolds or powerlog and the downpipe. zzp has some nice downpipes for the bonnevilles, 2.5" or 3"... ZZ Performance

Not to Thread jack, but does zzperformance have a powerlog for a 2000 ssei?

series II and series III you can bolt up the same headers