Depends on the year of the mustang, but the 2005 one ran 300 horsepower and ended with 315 in 2010. Many automotive sites, including autos.msn.com, will tell you how much horsepower any vehicle has.
315 horsepower
The 2003 Ford Mustang GT with a 4.6 V8 came stock with 260 horsepower.
V6: 210 Horsepower V8: 310 Horsepower
The 4.6 L , V8 engine in a 2007 Ford Mustang GT is rated at : ( 300 horsepower from the factory )
V6 engine - 210 horsepower , V8 engine - 315 horsepower
The 3.8 liter V6 has 190 horsepower ( the 4.6 liter V8 in the 2000 Ford Mustang GT has 260 horsepower )
3.8 liter V6 ( 190 horsepower ) 4.6 liter V8 in GT ( 260 horsepower ) In a 2001 Ford Mustang
In a 1991 Ford Mustang : The 5.0 liter V8 is rated at ( 225 horsepower from the factory )
The 4.6 liter , Single Over Head Cam , V8 engine in a 2003 Ford Mustang GT is rated at ( 260 horsepower from the factory )
2001 Ford Mustang : GT , 260 horsepower Bulitt , 265 horsepower Cobra , 320 horsepower
The 2005 Ford Mustang GT has 300HP
I know that my 1991 Mustang was rated at 225 horsepower , my 1977 was rated at 134 horsepower , and my 1971 Ford Mustang was rated at 285 brake horsepower with the 351 Cleveland 4 barrel