To give you an idea, I have SE254E cam's in my bike, along with full exhaust and the SE heavy breather intake. I also have the race tuner with the download that is ment for the open'd up air and exhaust combo. Now with the cam's added which are a tad racier than the 255's the bike run's ok. Smooth most of the time and fuel mileage is still near stock, but it does "hiccup" often on light throttle take offs and at idles it will "hiccup" nearly stalling the bike every now and then. Def. going to get this dyno tuned to make her run properly and squeek out a few more ponies too! So yeah if you change anything around in the motor, heads, cam's, bore kit, full exhaust and intake it's wise to get it tuned so it runs properly. If not you could cause damage mainly to your new exhaust pipes with blueing or yellowing from running to rich or worse yet having the motor run even more lean!
2012 Road Glide Custom Vivid Black named "Becky" with a simple motto "If it came from the factory like that, it doesn't belong on the bike!"