I think Borla has a reputation and that they know a thing or two about exhaust desing, if they just did a clone of the stock one why did they take so long to actually sell the thing?

Remember our cars are nor turbocharged, it's not just a matter of getting the largest pipe and no muffler at all to get the most power out of the engine, a free flow setup would actually hurt the performance.

I know because that's what my Magnaflow setup did, there was no power below 4,500 RPM, even if I could feel a gain in HP above 4,500 RPM.

You have to mantain backpressure to get torque at low revs, and also keep the gases hot in a naturally aspirated car.

Since I drive my car 80% of the time below 4,500 RPM, this works out better for me.