Any previous issues were resolved with the new engine, and there are no codes. When I deleted the o2 sensor of course I got a code for that. The power issue I believe has to do with air/fuel mixture. I think the decreased back pressure is causing a lean fuel situation. I'll know soon

that makes sense. I'll first attempt to restrict air flow through the hollowed cat and see if that helps. If not, I may go ahead and replace it. Thanks.

I also have an '87 F-250 with a 460, and there is a significant difference between the two. Are you suggesting that a deleted cat has no effect on o2 sensor readings or air flow?

I know it's illegal, but my 1989 F-250 arrived with a hollow cat. I installed a re-manned 460, and still lacked the power it should have. I was also stalling occasionally from a dead stop. I pulled the old O2 sensor and immediately picked up power and cured stall issue, so I replaced it. Old...