does anyone know much about/have what i believe is called an "exhaust dump." from what i can tell, it is just a pipe leading off the exhaust before the muffler that has a removable cap depending on whether you want the exhaust to go through the dump of the muffler. does anyone have one and advice about it? just putting a feeler out there because i would like to have one if it works how i think.

 

Correct.
However...

1. Check your local laws to see if this is legal.
2. I would go with an electronic exhaust dump. So your not going under the car all the time.
3. Your going to gain sound mainly and as for performance not as much as you would get with an upgraded downpipe and catback system.

 

and do s70's have what would be considered a 3inch exhaust?

 

No they have like a 2.25" exhaust system. So you would benefit to upgrade your ride to a full 3" mandrel bent catback system and Downpipe.