I put one 3/4" hole in them. A friend of mine put in two 3/4" holes and he also got flat spots and was much slower. The 3/4 seemed to work and sound ok. I also have the turn down tips which you can hear the sound bounce off the ground verses straight out the back. I like the set up.
after about 30,000 miles I wanted something a little different so I drilled one 1/2 inch hole in each side. I like it a lot just a little sound to let me know the motor is running and I didn't notice any change in performance.
I also drilled one 1/2" hole in each of my mufflers. I the cut a piece of stainless steel to made a "damper" to close the hole off when the noise bothers my wife. I just loosen the S.S. sheet metal screw,(it's in line w/ a "dummy exhaust outlet"), slide the S.S. piece back over the hole & now I'm stock again. The hard part was when the muffler tip screws snapped off trying to remove them. I just drilled the out, taped the threads, & used "neversieze" on new S.S.screws.
After you drill any holes in the aft chamber of the mufflers, disconnect the battery for about 15 minutes (if the bike had been running leave it disconnected until it cools down fully). This allows the ECM to establish a new baseline, within its adaptation parameters.
I have two 7/8" holes in each aft plate (in line with the false pipes); resulting in somewhat muted but pleasantly robust sound (a sort of deep base hum at cruising speed) with no flat spots, and noticeably (seat'o'pants) enhanced response performance. 'Sorry, no dyno data - just experience (and subjective impressions). Even riding two-up, it'll out-accelerate the dozen or so other 1800s (even solo ridden) in our riding group. Top (indicated) speed has been 134-5mph; GPS indicated 126.7mph. It's a 2001, non-abs, which has had the ECM change and head/coolant check (no issues found).
I guess I just dont have the kind of money everyone else here has..... I absolutely can not see myself drilling a friggin hole in my wing. But the good news is that I dont think I would want to either. I love the quiet but yet O So serious power of my wing............... i aint jacking with it..... more power to yall!!!!!!!!
last weekend at a SCRC meeting i met a guy that has a 1500 wing that he had someone install cutouts in. and is controlled by a lever on the right fairing.... when it is "in" it sounds like any normal wing, when he pulls the lever "out" it sounds like a porsche..... i was really impressed how that was done, and the awesome sound. i asked if he lost any performance when he pulls it out, he said "NO" not that he can tell....
Wondering if that can be done to a 1800 and not lose power....???