There is a benefit(s) to headers. Even on a stock 318 2bbl. Some disadvantages too. Some are personal preferences. Here is a list of some reasons someone might make this swap:
- Much easier to run your own dual exhaust at home. They make a lot of header back kits that can be cheap. Also, very easy if you choose to dump before the rear end.
- Performance - I did an ACTUAL TEST at the drag strip. I picked up 2.5 tenths and 2 mph in my van (stock 318 2bbl) in only the 1/8 mile.
- Sound. Some like the deep throaty sound.
- Looks. Many think they look cooler than stock manifolds.
I suggest buying a quality set (TTI or Dougs) and use a mini starter if you do make the swap.