Originally Posted by b3rndtt0ast
Wrong. Removing back pressure does not hurt engine performance.
Removing all back pressure with a full straight pipe setup certainly drops torque down a bit and I've seen it on multiple NA setups over the years regardless of the manufacturer.
Years back, I was helping a buddy with an exhaust system swap and we tested his setup with and without high-flow mufflers. Mid range power fell off completely in the straight-pipe configuration and after reinstalling the mufflers, it came right back.
Engine Masters has a few videos on the subjust and the lowest power output combo always ends up being the zoomie or straight pipe setup.