My wife has a new to her 2011 Super Glide. It is identical to her previous 2011 Super Glide. The new one only had 10,000 miles when we bought it. (Her previous Super Glide had 92,000 miles when we sold it.) She likes the color.
I swapped out lots of parts from old one to new one to make everything like her old one. The new bike had some type of drag muffler. They were very short and loud. I replaced those with her 10 year old Screaming Eagle mufflers. I did not worry about any tuning since all the mufflers moved around were not stock. Assumption was both bikes had some type of retune so I left that aspect alone. Both bikes ran fine both before and after the changes.
She is now interested in a 2 into 1 header/muffler combination. Any thoughts on whether this should be retuned or not?
Without trying to be vague- you won't know until you know. Can you feel something like a safe 14.3 vs a getting on dangerous 15+?
Or how about 12:1 vs 13:1? I've tuned some pretty big swings with muffler or header swaps. My advice is have it tuned.
At the very minimum you could pay a small fee to have it put on a dyno and checked.
One part of tuning is mapping the air flow through the engine. If you change this airflow though the engine. The modeling in the ECM also needs to be changed. From one slip on to the next. Might be close enough for no problems. But since you are changing the complete exhaust system to a completely different style of system. Plus the fact that exhaust has so much influence over the tq curve of these motorcycles. I would suggest a tune for this reason alone.
Not to mention the ignition side of tuning, and how it plays along with the fuel and air side.