I am only talking about ST11s, as that was what started this. PCs only work on earlier models of the ST13, so I hear.
I will get another dyno run done after I look at the carbs to check out the rich running. It has a very rich spike in the lower end, so something is amiss (running as rich as 10:1 afr low down, and 12:1 up top). No jetting changes are need with the mufflers, so I stiil have to address that problem reagardless of which mufflers are on it. Dyno runs do not tell all, as you would know, as throttle responsiveness etc does not necessarily show up. I am only talking about top gear roll on from 2000 to 3500rpm, so don't know what a dyno would tell you about that. Too much stock is placed on absolute dyno numbers, which tell you nothing much about throttle responsiveness and what a bike is like to ride. It is not a dramatic improvement, just a comment on pulling a bit cleaner down in the area identified as running way too rich with the standard pipes. Thats why I said it felt more tractable, not necessarily more powerful etc. If you had ridden the bike before and after it would have been on the noticeable side if you have any sensitivity for these things, but again not a dramatic change. An yes, I don't have a dyno run to show it does not run any better up top! I have tuned my older bike with slide carbs and gone through all sorts of adjustments to get it running properly in road conditions, from pilot jets, needles jets, slide cutouts. Establishing maximum power settings is the easy bit, diveability is much harder to achieve.
But overall, I agree with Jeff that putting an aftermarket system mostly leads to just noise and no or a loss in performance. I would presume the ST13 is similar, altough I have seem claims about improvements on the intake side.
The ST11 design does not lend itself to any dramatic improvements as the power delivery is designed from start to finish to give a flat power delivery with a broad torque curve. Getting the tuning right with the standard system is more important I think. If the mufflers I bought were not 1/4 new price I would have just fixed the bracket on the side that broke. If you check out
http://www.mcnews.com.au/ and look for 'muffler comparison' all you see is performance loss, or just noise for little or no gain.