This is a common question we get when discussing build plans with customers and friends. Sure external wastegates sound great, but are they necessary? Is it worth the money and complication in your engine bay for those sounds? The short answer is "at some point, yes". For those making stock to 350ish horsepower, depending on setup, there is not a necessity to move to an external wastegate. Internally gated stock turbos, or aftermarket turbos with them are more than capable of safely regulating boost at those power levels. So in our opinion it isn't worth the extra money and extra space they require.
The story changes when you start exceeding 400whp. Depending on the turbo choice and fueling you are using (93, e85, meth) you will start to run significant levels of boost. This requires your electronic boost control solenoid to regulate larger amounts of boost and the addition of an external wastegate can help bleed off boost pressure quicker and more accurately. It is at this point we start recommending you add a Tial 38mm external wastegate setup to your vehicle.
The 38mm wastegates can carry you all the way out to 600-700hp. At that point, if running a single scroll turbo, you would need to increase the wastegate size to a Tial 44mm. We also recommend running a 4 port boost control solenoid to aid in boost applications over 30psi.
We have solutions available for external wastegate setups with our partnership to Rise Fab Shop. We can add flanges to an existing wastegate and provide a screamer pipe as well as create the up pipe, ewg, and screamer 100% in house.