Sean - All of the above.

Bob's right about properly designed exhaust systems being
power-neutral over the design rpm range of the engine.

That's not to say that passenger car exhaust systems don't
reduce volumetric efficiency; thus (potentiallly) power & fuel
economy, but modern, properly designed systems are fairly
free-flowing.

The price of this happy situation is complexity - There are
plenty of things to go wrong, all of which degrade power &
fuel economy.

Most of this is covered by warranty, at least until you get to
the dealer & are told it is'nt, & will cost $1500 to fix.

On the bright side, do your due diligence & 8 years from now
you may well get a $11.82 settlement check from the class-
action attorney...

 Jack
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