OK...I've been reading a lot of posts where people are confused on how a wastegate works, and differences between wastegates. This is a brief explination with a lot of helpful pictures. Most of the pictures are my own, or friends of mines.
Here we go:
a. a wastegate is always located before the exhaust wheel.
b. It diverts exhaust gases around the exhaust wheel to control how much the wheel can spin - effectively limiting its ability to continue creating more boost.
c. a wastegate actuator is bascially a spring with a diaphram, the pressure(boost) your turbo produces pushes the diaphram to open the spring in turn opening the flapper door diverting exhaust gas.
d. With external wastegates you can change the "spring rate" by changing out the springs, this will either increase or decrease your minimum boost level.
Which is better?
If they do the job the way you want it to (control boost) I wouldn't consider one better then the other. I would say the external has a few more useable options with being able to change out the springs. Which by the way is NO fun at all, I upped my spring to 16 psi minimum and it took me and my girlfriend probably 10 minutes to get the hat back on the external wastegate.
here are pictures :)
this is a picture of an evoIII 16g turbo, the lower hole is the exhaust wheel the upper smaller hole is the internal wastegate passage (SAME place an o2 mounted external wastegate would relieve pressure from. all that would be done is the "flapper" (also could be considered a door) would be taken off and the hole would be ported larger.
Here is a picture with the flapper door open this diverts the gas around the turbine
here's a picture of a turbo INLET the hole in the middle/right side is the path the exhaust would follow toward the exhaust wheel
the hole on the left side is the wastegate hole, it will divert the exhaust around the turbine wheel, because it is placed before the turbine in the exhaust path.
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Here are a few different types of wastegate options/flavours.
EXTERNALLY DUMPED with internal wastegate - uses your stock wastegate flapper, but instead of the normal re-route like your stock o2 housing has, it pipes it off to the atmosphere like this:
RE-ROUTED EXTERNAL wastegate this is on the o2 housing, which attaches to the turbo, in this setup the stock internal flapper is removed the shiny thing(external wastegate) replaces it- IF you were to want this type of setup dumped to the atmosphere you would simply not re-route it back into the o2 housing and just attach an open air pipe.
EXTERNALLY dumped, external wastegate welded to the manifold(I do not have a pipe welded onto it yet, it IS dumping into my engine bay (bad) the car is not a daily driver and I will be taking it to a shop to have it re-routed into my downpipe):
