How hard wold it be to put a 4 inch down pipe on a 95 f250 5 speed 4x4? I can get one for under 50 from a guy that totaled a truck

 

4 inch would be a real bear to put in, doesnt gain enough more than a 3 inch to be worth it, go 3 inch down pipe, (might still have to push back the firewall), and go to 4 inch after the down pipe and get rid of the converter and muffler. The converter is the biggest restriction in the exhaust on the obs powerstrokes.

 

you cant fitone without a ton of modifying to the firewall