If those pipes are literally straight 2" pipes back from from the factory collector, quite likely, 84's are still "Carter" bikes and lean to start with, and its an Ohio built bike-
assume nothing, do the typical plug cut off testing. But at least one or two step ups I'm guessing.
First of all, you won't get any more power, you will actually lose quite a bit. But you will get a lot of noise if that is what you want. You will need to go with much richer jetting.
I don't recommend straight pipes. This is not a lecture about loud pipes. The reason I don't recommend them is that they have almost no back pressure, and and the engine and intake system is designed to run with back pressure. The big probllem comes from the fact that they do have some backpressure, but it will vary widely over the engines rpm range. Since proper air/fuel mixture requires fairly consistent back pressure, which even loud aftermarket pipes have, there is no way to properly jet the carbs. Carbs cannot be tuned over the range of back pressures that open pipes have at different engine speeds. The result will be that you will be way to rich at some speeds, and way to lean at others. This is a fairly efficient way to kill an engine.
Many Harley riders used open pipes anyway, even knowing what it would do to their engine. When fuel injection came along, they first hated it, because it was not traditional. They quickly learned to love it however, when they found that it, unlike a carb, could be tuned to provide a proper mixture over the entire rpm range, while still running open pipes.
Had a 1100 that was a beater bike we built just out of boredom.anyway ran straight pipes,and ran like @^%$.Lost about 1/2 HP.The back pressure was non-existent.Solution we came up with was adding some of the washers from a old set of rear air shocks from another 1100 on the end of the pipe.Gave it enough back pressure and still had the loud sound that we were looking for.The pipe was 2",and once we welded the washer on the end had a 1 1/2 opening.But I would not recommend as each bike is tuned different,and we got lucky,did a lot of trial and error before getting it close enough to right.And if the mixture isnt right you can run too hot on the pipes and blue them if chrome.Since the one we chopped was a wreck to begin with it was more a fun thing than a everyday rider.But did turn into a daily rider for someone else.But I am a firm believer in a bike is a extension of the rider,and I have never been the norm,currently have a 1200 that is getting a make over this winter.