The answer to this question depends on a variety of circumstances:
1. What size is the engine? Larger engines benefit more greatly from increased exhaust flow in most cases.
2. What size headers are you thinking of using? Choosing a primary diameter that is too large or too small may reduce your total power.
3. Headers alone may not have much effect on power if the engine already has a decent set of exhaust manifolds and/or has a restricted intake system.
20-25 as a rule of thumb. More with good heads.
10hp
yes
69
bout 10 to 25. depending on what size of motor
There are many easy ways to add horsepower like.... Air intake system headers performance chips turbos basically whatever you can afford cause parts tend to be pricey
adding headers will allow engine to breath better and boost up horsepower but not by much, headers also make you vehicle louder with pipes.
what year
Maybe 10
if you can find the hp. of the eng., you can add between 12-20 more hp. for the headers.
The 2000 Ford Mustang GT was rated at 260-horsepower
Not enough to even notice.