I am looking for dyno tunes on bikes that have not changed their exhaust. (Slip ons ok)

Almost all the information I am finding has a tune done at the same time an exhaust has been changed. I am curious to see how much is the tune and how much is the exhaust.

I am curious as to what can be done with a stock 'Tommy Gun' style exhaust as I like the look of mine and you don't see too many 2-1-2 around.
I have come across one LR-S that did a 117 swap on a stock exhaust. When he swapped in a TBR 2-1 later he only had a ~3hp/tq gain and lost some bottom end pull. While possible it was the pipe choice, it is interesting he barely got any gains over a tune on a stock exhaust. This makes me wonder what the stock pipes are capable of achieving with less restrictive mufflers.

And I've come across dyno comparisons on a Sportster 1200 that just changed out slip ons and didn't tune and they were seeing a gain of about 10hp/tq. This leads me to believe a lot of the restriction is found in the muffler and not the pipe.



I know a good system from top to bottom will provide the most gains, I am just curious as to how much is from a full system vs less restrictive mufflers and most of all, the tune. It would be good to know how much can actually be achieved with just a tune and slip ons vs assumptions and "needing" to change out a whole system. I am thinking that a good tune and good slip ons could result in about 95% of the power gains a full system can achieve, and may have a smoother curve and better bottom end.




Just trying to figure out what's true and what's just repeated information.

Thanks