95 Cummins exhaust question

[Dan Dargeloh]

I've got a 1995 3500 dually with the Cummins engine. The previous owner's son straight piped the exhaust. While not being obnoxious, the exhaust is louder than I'd like. Outside of one of those curved round intake tubes the engine is still totally stock at 160 horsepower. Would a 4" exhaust with muffler offer any advantage over the stock 3" system with a muffler reinstalled on a stock engine? I also wonder how many of these old 2 valvers like this are still running without having been turned up?

 

[dapepper9]

There's some benefit from turbo efficiency though it's not a massive increase