Just to add my 2 cents...
What you want is 300 feet per second pulses flowing out the pipe (whatever configuration) and if you have an open muffler (or baffle too open) you lose that flow. That Large opening distorts the flow so it bounces back at the wrong timing and you have the dreaded reversion, A backwash of burnt air/fuel bounced back into the cylinder that people call "not enough back pressure".
May not sound right but I know what I'm thinking :bigsmiley30:
And what Mr D is talking about is rolling in traffic from a light running like a dog, Not WOT at 3000 - 6000 rpm
Oh and BTW the cones some folks put in are not to make back pressure but to block the reverse flow at lower rpm in pipes that are large because they are tuned for high cubes running high rpm.
