I have a 1991 F250 I just finished rebuilding the 351W adding a 35-255-5 Comp Cam 9.14:1 pistons, I built it for towing and hunting off-road at 10,600ft. I just passed it through emissions so I am good for 2 years, I want to open the exhaust up some to let her breath this fine mountain air but in 2 years I will have to pass emissions test again, anyone know what mods can be done to give her room to breath and still keep her legal with the emission ****'s and not foul the emissions set up on the truck, I hate check engine lights, lol. Any ideas?

 

Becasue you are akin to the low end grunt, I would not go too big on the openings. Some long tube headers and then mild flow-throughs would be perfect, depending on your budget. To start with, I would look to open the after-cat up a little with a bigger pipe or duel exits. I can recommend two guys, you can stop by and chat with them for ideas and prices.

Scott at AA performance exhaust and brakes (Hampden and Broadway area)
Cory at House of mufflers and brakes (Evans and Colorado area)

Both good guys and I have experience with their work and products.
--Mike