Why is 98gt different
 

I've looked through alot of books trying to figure out what the difference is in a 98gt from the previous 97-95. Horsepower is increased through the years but I cant find anything else. In products such as shift kits, computer chips, blowers I have found that the companys like to exclude the 98gt. Why is this

The difference between the 96-97 and the 98 is Ford changed the exhaust header configuration a little on the 98 and that's why it has 225 hp whereas the 96-97 has 215 hp stock.

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1996 Mustang GTS: 5-speed, K&N, removed air silencer, 3.73s, turndowns after stock H-pipe (no mufflers)

I was under the impression that the extra hp came from a more aggressively tuned computer.