I was wondering what's the differance between external dump and internal?? What would i have to do to switch to external??

 

if your talking about wastegate dump, then "internal" is referred to as recirculating dump, which flows the wastegate gases back into the stream of the exhaust gas. this causes turbulence in the exhaust flow. all evo's have this, their o2 has a slight split but merges back.
image taken from megan racing, recirc o2 housing


an "external" dump for the wastegate is when the wastegate gases exit through a tube and into the atmosphere while not flowing back into the exhaust. this creates no exhaust gas turbulence and have seen to gain power. but it is louder since the waste is not muffled.
image taken from MAP, external dump o2 housing


if your talking about internal or external wastegate. then the stock evo's come with internal wastegates implemented in the exhaust housing. the waste is released via the actuator that is visibly mounted on the turbo. this releases the waste gases into the above situations based on actuator spring and boost setting.
image taken from tomeiarms, stock frame turbo with internal wg


external wastegate- you cannot reuse the stock turbo since they have internal wastegates, you would need a new exhaust manifold with wastegate ports (single or twin depending on single scroll or twin scroll turbo) and an aftermarket turbo like the garrett gt30r (example) which does not have an internal wastegate. you would need to purchase wastegates for the manifold and make dump tubes for them. you wont be able to use your stock o2 housing since it wont fit with these types of turbos.
image taken from ets, twin scroll setup with dual wastegates.