I have a Header for 1989 F-150 6 cyl 300 4.9L. It actually turns the single exhaust into a dual exhaust system. I have yet to be able to find anyone that makes a header for this engine. I got it from a friend who owns a boat marina. I don't know if I am going to go through the trouble and expense to install a complete new exhaust but was curious if anyone might know who could have manufactured it and what it might take to make the adapter for the O2 sensor. Would I need a sensor for each of the header connections and a cat for each as well for inspection purposes?

 

I'm not sure how you would tie in another sensor, but to meet emissions you would need a cat for each pipe.

 

I don't know specifically who made it, but I know that headers used to be made for the 300 6's in granadas and whatever the mercury version was i think the montego or zephyr? Anyway they were fairly popular all throughout the entire life of fords 300 6 because of it's popularity and reputation as a really good torquey inexpensive powerhouse. I'm not sure how common this is but my 1994 F150 supercab xlt with the 300 6 came with a split exhaust manifold that has 3 cylinders on each side of it that went into 2 separate pipes that went all the way down to the convertor which had 2 inlets and one outlet. In your particular case you could easily set it up like that and get a dual inlet convertor. Also the o2 sensor can be mounted on either pipe and it doesn't matter which one considering the antiquity of the onboard diagnostic system not being smart enough to know the difference. mine was mounted on the bottom pipe of the 2. You can mount it almost anywhere before the cat and if your pipe doesn't have a fitting for a sensor you can buy one from summit or jegs. It's so much nicer living in an emissions exempt state. It made my exhaust work a lot easier and it's a lot easier to make horsepower by eliminating the catalytic convertor but I realize that it can't be done everywhere. You can also purchase high performance or high flow converters, but the bigger ford engines of that era or vintage are particularly dirty and notorious for failing emissions testing.