You can get tuned pipes from Spookytooth and Sick Bike Parts. Some of the engine sellers also have what they call a Poo Poo Pipe which doesn't help performance but it does put the muffler behind the rider.
I bought the first one from boygofast- it'sa longer pipe and a longer muffler too. It is designed to run down and over the top of the bottom bracket- so the clearance is very limited at the cranks and even off the motor, past the down tube- it didn't fit on my Micargi cruiser with a 66 motor- but it does look like it will fit the Schwinn Traveler with 49 slant I'm building now-- so I'm happy, it looks great! but don't recommend for cruiser. The more seasoned mechanics can probably make it work.
The more pricey from livefast motors drops further down BELOW the bottom bracket, and so clearance is probably not as critical- and it's longer and probably more quiet- can't say anything for sure- haven't seen it and it's sorta expensive.
in the picture below the first pipe is just hanging unattached but will draw tight up next to the chain stay when installed.
I would very much recommend a tuned exhaust, while not the "cheapest" it defo helps the motor perform significantly better. My exhaust system not only helps performance - but brings the exhaust outlet all the way to the back of the bike so I'm not sittin' in a cloud of fumes at a stop light lol;