Actually they claim a "max horsepower" gain of 5hp. And they include the disclaimer that it varies by vehicle.
I don't know about any HP gain on my 08' but I will testify to better gas mileage. Was running 26 MPG prior to install, now running at 29 MPG (purely in-town mpg - zero hi-way/freeway miles). It also pulls much better through the entire power range.
If you happen to have a car with a great ground system already, you won't see much if any difference. But Ford didn't even bother to ground the throttle body on the 08' and it's fly-by-wire now. Simply grounding the throttle body alone makes a big difference on the 08'.
Best wishes and keep on modding April 2009 SOTM, July 2009 ROTM, 2009 FF ROTY
RIFF CREW, Sedan Revolution #137, TEAM Duratec #181, Bremerton Raceway #658, NW POSSE #6