Has anyone cut one of these open ? Im wondering if it is a wide open stamped box or is it just a cover with bent tubing inside in which case the pipe diameter would most likely be extremely small at the sharp bends.

 

Not trying to be a smart *** but I think this should be OK. Hopefully the manufacturer knew what they were doing.

 

That picture seems to be comparing the OEM early “rams horn” style modular Y pipe to the SPD aftermarket Y section, there will be very little if any gain to be had from swapping to the SPD from the rams horn. As that picture shows the rams horn setup really isn’t too bad for decent flow. The later OEM necked down T shaped Y pipe is where the SPD or other smoother flowing Y pipes would bring a small performance gain. My Banks headers came with a smooth Y pipe but I obviously can’t compare it to my factory T shaped Y pipe because of the headers also being part of the upgrade. The factory exhaust manifolds seem to me to be the bigger exhaust restriction, but I’m not an exhaust expert or engineer………but the truck pulls better after the headers.

 

Never assume that, sometimes they just do what is cheap and easy. I bought an aftermarket replacement y pipe once that had 2" headpipes that looked like they were crushed together in a forming die to fit in a section of 2.5" that was slid over them. There was a huge decrease in performance when I installed it. I cut it open, the headpipes were about half their original diameter, I cut the crushed parts out so it was wide open through the junction and it was back to normal.