Whats been done now?
If so, id expect about 165-170 max (on a good day). 189BHP is very very high.
Dynos are fickle things - ive seen articles about people taking their car to 1 dyno, getting xxx BHP and then driving it to another on the same day and recording 20 or 30bhp difference.
TS engines dont respond massively well to tuning. Squadra and Alfatune only advertise about a 5-10bhp increase I think, and they are considered to be the best in the business.
A filter doesnt really add anything at all, maybe 1 or 2bhp (maybe!). A free flowing exhaust might pick up a couple as well. At the end of the day id only expect these mods to gain 15bhp max over standard, so about 170bhp.
Thats before we take in to account the fact that some ponies will have bolted from the engine over the years.
So, yup, I reckon 189bhp is a very high figure.