where is my flat spot coming from? (for people w/ exhausts?)

[davidpertuz@mindspring.com]

I have a flat spot in my powerband that
comes in at around 4200 rpm and is maybe
500 rpm wide. A month or so ago I took
off my (original) stock muffler, which
broke, and have been driving around muff-
less since then. Although I didn't notice
it for a week or two afterwards, I'm pretty confident the flat spot is exhaust-related.

Do any of you with aftermarket exhausts
have a similar flat spot? I'm curious.
My car, muffler-less (but with the
resonator) sounds like a lot of the aftermarket-exhaust-equipped cars I've
heard, and I imagine perhaps the
restriction is similar.

I should have a new stock muffler back
on by Saturday, so I will see if that
was the cause. In the meantime, I'm just
curious. A recent thread put this in mind.

thanks,
david