so run an open header then? no...
oh but then the power under the cam go's away and you find yourself tuning a lil richer and using more throttle to get up to speed...
I'm talking mpg, not ultimate power...
why do you think that way?
Uh, because you are incorrect. An open header, PROPERLY JETTED will not require "more throttle" and will in fact give you better mileage.
This thing is not a two stroke.
The only reason cars have exhaust systems made the way they are is for cost, noise, and emissions.
EDIT I see you are already talking about OPEN headers, and I was thinking the OP was talking about the MUFFLED EXHAUST SYSTEM, IE from the header/ manifold and back.
You are right about an OPEN header, low end torque will go away if too big. I doubt this is possible with a system clear back to the bumper, unless it's literally dragging the ground.