Like the old and worn out Harley line goes....:loud pipes save lives. That is BS. Only thing loud pipes do is irritate the voting public who then legislate noise abatement laws.
If you come right sown to it, it's not the exhaust that produces the noise in a diesel engine, it's the retarder or as it's called the 'Jake Brake' that produces the irritating noise. The turbo does a good job of breaking up the sound waves that sound like 'noise.
I agree completely with you on the Harley (or any bike) with straight pipes. You can't hear them coming any better than any other bike since the pipes are aimed behind them. I can only imagine lots of the riders will have hearing loss due to the noise.
In my experience the amount of exhaust noise compared to Jake brake noise from straight pipes on trucks is about the same, although the Jake brake noise is a little more sharp, more of a popping noise.
As far as turbos go, they do a small amount to muffle the exhaust noise, but not enough to make it acceptable, in my pinion. I spent a couple of years on an International E270 Payscraper with a DT573 setting right next to me, whose exhaust pipe stuck out of the hood about three feet and I have got hearing damage and have had constant tinnitus ever since.
Those jackasses with Cummins and Duramaxes with straight pipes and the fuel turned up so they belch balck smoke when they punch it should be arrested for violating noise and pollution laws, and the trucks crushed.
Let them go to the county fair and enter the truck pulls to see just how tough they are, but don't do it on the street.
I don't know what kind of marginally intelligent people they are trying to impress, but they don't impress me.
Rant off.
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