Yup
Thats what I started with.
You wont notice much driving wise, unless you mount it the car frame in which case you'll hear a constant tap tap tap so i suggest you mount it to the airbox or something else thats somewhat suspended/dampened.
What you'll notice in the logs is that the boost will overshoot the target on spool up since the 3ports acts much faster that stock, then error correction kicks in and brings it back down below your target and then upward corrects etc for about 500-1000rpm until your boost curve is "settling" .
By overshoot I mean 1 to 2 psi from your 21 target so your still in the safe zone.
With a very minimal tweak you can tell the 3port to not act as aggressive at certain times so that the ecu has to do minimal corrections and you get to your target boost right away.
Its just a valve that opens and closes on a set cycle. Faster the cycle, quicker you'll build boost/more boost you can maintain since the actual wastegate on the turbo "sees" less pressure.
If you take a look at the reactive WGDC maps under the Turbo section in ecuflash you'll kinda see the trend. You want to build boost quickly at low rpm then balance things to get a flat boost curve, and then at the high rpms try to hang on to the boost as the trubo runs out of puff.
I found that for my car and 3port, i was overshooting so i reduced the values in the lower rpms and fine tuned the middle section.
Now if your logging, the car will actually tell you how much its had to change the maps by and when. You'll see that the ecu has either added or subtracted from your WGDC map what it requires to hit your boost target map at a certain rpm. So to help out the ecu and reduce the correction swings you can just add or subtract your map by the same!!