I have a 1999 502 MPI. When I took off the stock exhaust manifolds in order to replace them with a pair of Rex marine manifolds I dicovered rust in the exhaust port of the #4 and #6 cylinders. #2 and #8 where OK. Any good suggestions as to the cause? reversion? exhaust riser gasket leak? Do I need to do something or will I be OK just by using the Rex manifolds from now on?

Sounds like leaking riser gaskets. As long as you are addressing the connection at the risers, your problem should go away.

BT

Its most likly condensation ! don't worry about it ,

I would think condensation would be equal on the odd and even banks. No rust mentioned on the odd bank. Was there any? Look at the old risers and see if you can note water trails and where they originated.

BT

I'm with BT on this one. Being that is only on 1 side and the problem is in the center 2 cylinders, sounds like riser gaskets to me.