OK..first of all..he said its a 2002 mustang. That means it's Fuel injected. Therefore, he cannot just "get straight pipes" He would, in addition, need an 02 sensor eliminator, which fakes the voltage from the 02 sensor back to the ECU to tell the engine that it's mixing fuel and air in the correct proportion.
Next...so long as you don't run 10 year old oil...there really is not much difference in the 5 dollar/quart oils and the 2dollar/quart oil. You don't "gain horsepower" by using a different oil.
Ok...you started on the right path with the "plugs and wires" idea. However, you're not gonna gain HP, you're only returning effecincy to the engine by replaceing the plugs and wires. Since it's a 2k2, i doubt it really needs new wires at all. "racing wires" don't give the plug any more voltage than a stock wire. The resistance in a stock wire is less than one tenth of an ohm, much like about ANY wire will be.
Well...once again...you started on the right track. Yes, an air intake will help the engine, in fact it would actually gain maybe a few hp. Nothing you would notice on the butt dyno, tho. It's more for show and the roar. Yes, i admit, they are an improvement over stock air intake, but its not more than 3~5 horsepower.
A nice cam? Do you even know what the hell a cam IS, or what it's job is?
And, once agian, since it's a 2002 mustang, his engine isn't "chippable."
OBDII = no chip.
Go kill yourself.
-Dave
