They're not weak, but later motors had lower compression.
There's dumb things that can make engines louder. Like retarding idle timing.
The cam has a huge effect on the sound, but the bigger the cam the higher the compression should be. Too much compression without enough cam and it'll have issues, but big cams also tend to perform at higher revs - so there's such a thing as too much.
Are you running manifolds? Those will be quieter than headers too.
