A good friend of mine installed a set of 21's in his 03 Heritage upon my suggestion and it did 75hp and 95tq. It was a carb. bike with longshot exhaust. I rode it and that thing pulled like a freight train right off the git-go. I also installed some 26 cams in another friends 03 heritage with the same pipes and the 21's had a better feel to them, especially on the bottom.

 

They Will...that 5* intake closing difference will make a lot of difference on the bottom.... I also like that the 21 has a little more lift...

 

Did you notice any difference in vibration between the two? I've read some complaints about low rpm vibrations with the 21s but it seems like it's only a few riders and not recently

 

Not really, the 21's were very smooth but so were the 26's. Again I'd shoot for the 21's imo.