I'm running 12:1 compression with stage 3 PI heads and stage 3 N/A cams. You want to know what I put down on my tuners dyno? This is why I am personally telling you now that dyno numbers really ain't squat man. Every dyno is going to read differently and to be honest a mustang dyno will read lower and can read very low like mine did. That's why I was telling you track times and what you can do with the car is what matters. Hey this is a free country and if you want that 255 RWHP then you go find some over rated dyno that reads stupid high. That is my advice as the best mod for you if you just want to see the numbers and stop worrying about it and actually feel the power.
LT headers with good exhaust, CAI, Throttle body, Plenium, and a good tune. That is going to be your best bet honestly. Who cares what the numbers are because you are just wanting to do basic bolt ons.
You want to make a real difference with that and make it count. Weight reduction, suspension, along with a good set of sticky tires and that will be it.
I really do agree on what Fordman says, the numbers ain't squat! That being said, for those who only know what brand and horsepower their car has, it's is nice to say you have 300 hp. They don't need to know if it is crank or rwhp, they won't even know the difference. It is more for the bragging rights in those cases. When I tell people I drive a Mustang, they ask me two questions: 1) Is it a V6 or a V8? and 2) How many horsepower does it have? 200-299hp cars are so common these days that the number 260hp doesn't impress anyone, but if you can say you have 300hp most people go "Wow, that is a lot! I bet it's hella fun to drive!"
You get where I'm going with this, I am well aware that the actual noticeable difference you get from bolt ons are negligible, and that in the end it all comes down to the right combination between bolt ons, gears, tires, suspension, and of course the driver. I have my '03 GT and I love it, I did suspension this Christmas for handling and appearance purposes. Next I plan on getting gears and a tuner, possibly a CAI for looks. After that I don't feel it's worth dumping a lot of money into unless I decide on going F/I later on.
Sorry for hijacking the thread, but I wanted to share my views and opinions, as they are relatable to the topic.
2003 Mustang GT
Intake & Exhaust: K&N FIPK CAI, Mac O/R H-Pipe, Custom Catback w/ Magnaflow Magnapack Mufflers.
Suspension: H&R Super Sport Springs, KONI STR.T Shocks & Struts, J&M Caster Camber Plates, Steeda Bumpsteer Kit, UPR Elite LCA's & UCA's.
Performance: BAMA 93R Custom Tune, FRPP 4.10 Gears w/ Terminator spec T-Lok.
Planned Mods: FLSFC, Eibach Sway Bars, Throttle Body, Plenum, Rims.