I too was a little baffled (no pun intended!!) at such a huge loss in power, but in a conversation with Chris (CJS) he mentioned one system in Europo call refer e that uses a restrictor before the muffler that cost him 17HP.
Big difference between 17 and 45!!
But I checked anyway. 5-10mm holes. 392 square mms.
Compared to 2,290 square mm for the pipe. 17% of the area of the pipe.
I couldn't start tuning until I figured it out. You must not [waste your time] tuning a broke engine!!!!
Typically a dB killer is the insert at the rear of the muffler. The LV does have one of those too. I prefer to call it an HP killer!
Once that was out of the picture, I proceeded with the tuning. This is my first Mitsubishi ECU tune, with new software, but it isn't my first ride on the merry-go-'round. (I have used the rest of the tools.)
Once I pulled the cork out of the pipe, it felt like a Ducati instead of a Moto Guzzi. (ouch!!!!)
I don't understand why Greg's is the first, (maybe I'm invisible, or am I not spending enough time self-promoting?) but now that I have the tools and the knowledge....