I am pretty new to the turbo world and I was just wondering what the different sizes of exteral wastegates actually do? For example, what application is a 38mm WG needed vs. a lets say 44mm. What does the size of the WG actually do?

 

The size of the wastegate, along with the stiffness of the internal spring, dictates the amount of exhaust that can bypass the turbo. Basically the size and spring pressure are two key elements in determining how much boost your turbo will make.

 

OK, so for instance if I only want to make lets say 5 lbs. of boost then a 38mm WG or smaller would be sufficient? But if I want to make lets say 20 lbs. of boost I would need a considerably larger mm WG? Is that about right?

 

no not really. The engine size is also need for gate size. 38MM stuff is good for 6.0 and down. Running what ever boost you want. The larger gates are needed to bypass more air away from the turbo.
Large engines hi rpm engines move alot of air. You have to get that exhuast away from the turbo other wise you will never be able to run low boost.
thats its job to be able to move enough hot air around the turbo so it does not built more boost then you want.

 

Yep...think about it like this. More exhaust moving through the wastegate means less exhaust moving through the turbo, which means less boost. As I said before, size is one factor. Spring pressure is also another. Spring pressure can also be modified with the use of a boost controller. As Trick stated, engine size is also a factor in determining which size WG you need. Too small, and you'll get boost spikes at higher RPM because the wastegate has reached full flow capacity, so there is nowhere else for the exhaust to go other than through the turbo.

 

So is a 38mm WG plenty big enough for a 5.3L in any application?

 

Should be fine.