Flowmasters sound good on fox body 302 mustangs. They had a unique sound to them on the roller 302.
I have ran them on 340's but they are loud for sure. Now im running TTI exhaust on both of my cars and the dynomax super turbos that came with the kits.
I can say one thing about these mufflers. When I first put them on I did not like them much. After about a month or two they got a little louder and sound really good.