2000 28 sunsation 502 100% stock, what kind of aftermarket exhaust youthink I can run ? I was told call CMI?

Can't go wrong there. I just ordered the Platinum series. Talk to them about tailpipes though - mine needed to be custom bent, which drove the price up a bit (port and starboard sides were not exactly mirror images of each other, but I'm told this is pretty common). Total, they were around $2500.

You say custom bent did you have them do it? what kind of boat do you run? did you have to measure first or they new what size and bend you need?

I run a 2001 Aggressor with a tall deck block (572CID). Call them up and see what they have to say. Yes, I had them do it. We had to measure (with no exhaust on the motor). Your application may be much different, and maybe off-the-shelf tailpipes will work.

oHHHHHHHHHH ok

Dunno how familiar you are with marine exhausts, but don't confuse the tailpipes with the exhaust tips (which are visible from the outside of the boat, on the transom). You need both, assuming you want to keep your OEM exhaust tips.