I have an 89 FLHTC EVO 1340 and it has the power curve true duals chrome crossover header pipes with slip on mufflers. I repacked the baffles and its still very high pitched. I want the bike to be a low thunder sound not a high pitched yamaha dirt bike. (ok a bit over exaggerated but you get the picture) the baffles are removable but Im not sure what to buy.. what do shorter-longer baffles do. how can I change the sound without replacing the entire exhaust system and advise would be appreciated. thanks

 

Have you taken the baffles out to see if you like that sound? Maybe get a wood stove.

 

S&S Slip ons sound the way you want the bike to.

 

Monster ovals have the sound you desire, but they ain't cheap.
I have Cycle Shack 3 inch up slash MHD-291 SU slip-ons. They have a really nice low mellow sound with the baffles in, and a very aggressive "cherry bomb" sound without the baffle. I'm an old school hot rodder, so I prefer the "cherry bomb" sound. Especially the cackle on decel.
Anyway, they aren't bad priced. I picked mine up on eBay for 70 bucks shipped. They are blems though. The mounts are just a tiny bit off from one another, but adjusted to match, I'd have to show you for you to see it. But still under 3 bills from Cycle Shack.
I have 2 inch header pipe so no flares. If your pipes have flares, they sell a set for those too.

 

If the baffles are closed at the entry area deflecting the pulses directly into the packing, you can drill a hole in the entry area and allow more pulses to escape direct.

Shortening the baffle will make it noticably louder but may or maynot change the tone, it is all trial and error.