Is your car a 6 speed manual or automatic? 225 at the wheels is in the range or rather above average that is fine for a 3 stage manifold swap car, at least a manual. You should feel a nice difference though specially midrange and up. That's only 25hp drivetrain loss from 255hp which is 10%.
A dyno is only a good tool if you get a baseline because then you get to compare upgrades. Comparing one dyno to the other will never be exact.
If you want to double check against other NA dynos there's a whole thread here:
Https://www.E90post.com/forums/showthread.php?t=916863