I have a 2005 Ford 250 HD diesel truck. Where I live a smog test isn't required. I'm not even sure if the truck has a converter, but if so can I remove it and increase my fuel mileage? Also will dual exhaust help?
Where do you live that they don't have emission testing?
If you remove the catalytic converter you violate federal emission regulations. If you are caught you could be fined.
If you remove the catalytic converter there is an oxygen sensor in the exhaust. The missing converter could set an emission code in the computer memory setting a trouble code.
Removing the converter will probably give you a little more power but not so much as of the fuel economy.
If you are looking for increased power and fuel economy then your truck diesel may qualify for a power chip by a company called Hypertech. Your local speed shop may have a power chip or system that may possibly be installed on your truck. This can be adjusted to your preferences for power and economy.