I have run the Two Brothers and the Delkevics. I prefer the Delkevics because the TB's are loud by comparison. The cost of the Delkevics are by far less.
No jetting is necessary.
I work on and rebuild both ST11 & 13's and have done modest carb re-jetting along with removing/blocking the PAIR system. Removing the PAIR system will greatly reduce the popping from the exhaust which was annoying with the two brothers exhaust. The jetting helped with launching the bike from a stop, (the low or slow jets) and the mains were increased slightly to the Canadian spec., along with modest Air box mods. The overall package was very good with a slight increase in fuel economy and a general feeling of increased performance.
I need to add that I did a complete service on the bike with carb sync, plugs, air filter, valve adjustment etc. etc...
The gains were from all of the above and not from just exhaust or jetting or air box mods, and definitely no gain from the PAIR removal.
Personally I don't think that it is worth doing unless you do everything yourself. The design of the 1100 engine is for stability and low end power with a nice smooth and strong mid to high RPM's Power.
I lost all my notes with a computer crash but I'm sure there some of us who could gather all the info if you wanted to do all that.
Bob
On a ST1100 is what I am wondreing about and if you are what brand. I have never seen a ST with aftermarket exhaust so not sure of what it would sound like. Does it require rejetting? If so is that something a average joe that does most of his own work could do.
Thanks.
Paul