Exiting to come right back

I have a 5 year visa for Brazil, am here now. In a month I will be approaching my 90 day period.
My intent is to leave the country for only 1 or 2 days and come right back in to continue my other 90 days allowed. What is the best country to do this in South America? also one which I would not require a visa.
I have an American passport. Thanks for any help and suggestions.

Most  countries  do  require  a visa  and also reciprocity  fee for American  tourists.  If you  have  a 5 year   visa,  why do you have  to leave  after  90 days?

The maximum  you can  stay is 180  days  per year  that's  6 months  in Brazil  then   6 months  from  when  you  leave.  If you  want  to  extend  your  90 days, best  just going  to  Federal  Police  office  about  8am  3 days  before  90tg day.  Make sure  you have all  the right  documents  and  have payed  the fees   required.  That's  the  I've  done bit over the  last  four  years.

Also go too  one  in Niteroi  rather  than  the  airport,  if you're  in RJ.