Measuring boost back pressure

Thanks @TT5.9mag. As always I appreciate and value your feedback.
The exhaust outlet on this eBay model is 3” so that’s where we’ll stay.
I’m not quite ready to throw in the towel on this turbo but the back pressure numbers are informative. I know a 1:1 ratio is ideal and 2:1 is not uncommon at higher PSIs from what I’ve read so I think this turbo still has a little more in it given the back pressure is somewhere in between at 11psi when I just run just the downpipe. Not sure my motor or injectors will scale much higher than 15-16psi anyway. I need to get the tune squared away at higher boost (still a bit rich) and take it to the track and see.