an external wastegate will allow better boost contol because of a bigger puck,here is why........ your exhaust gasas are what is used to spool (spin) the turbine wheel which spins the compressor wheel on the other side of the shaft,which creates boost.the more exhaust that is allowed to spin the turbine wheel the more inlet air you'll compress,the more boost you'll create.a wastegate is basicly a valve that opens at predetermained(by chip,wastegate rod setting,manual relief valve,bleeder valve,or by what ever means of boost control you are using on your setup)amount of pressure (boost) in order to regulate the boost by allowing exhaust gases to bypass the turbine wheel there for not providing as much gas flow to spin the wheel as fast,there for not creating as much boost.(hope this is making sense)...its like a fuel pressure regulator,only its regulating boost..i'm not sure but i think the valve(puck) on a terry houston 3"downpipe is like 1.3" ,atr 3"dp is 1 1/2" both are internal,which are bigger than a stock elbowed puck..this allows better boost control because it can let more exhaust gas out than a smaller puck..as for external wastegates,the deltagate has a 1.25" which is rated for like 450hp but a racegate has a 1.65"puck is rated at 900hp,atr's billet wastegate has a 1 3/4" puck...i'm sure there are lots of other details that i'm missing.. please experts join in....this is just a raw version of how i understand they work... a bigger puck allows for more better boost control with less likelyhood of boost creep(where the exhaust gases out flow the wastegate puck which in turn allows more boost than what was set by boost controler) and more consitant steady control of boost without surge(or as much)........well thats my understanding of it anyways....hope this helped a little..hope it didn't confuse you anymore than might be.........joel