I put one of the stock downpipes on the flowbench to see how it would perform. This was a gutted stock downpipe, meaning that the pre-cat had been removed to try and improve performance. Had the pre-cat been in place the pressure losses would have been greater.
For comparison I used an Autospeed mid-pipe. This isn’t a direct comparison because the downpipe portion of the Autospeed downpipe, which runs from the turbocharger to just past the flex joint, was not in place. Because that missing section is nothing but a smooth curved three inch pipe it probably would not increase the pressure losses very much. At some point in the future I will try to do a better comparison test by using the downpipe.