I heard replacing stock plugs with performance ones makes the engine run better/faster. I know iridium are the best but the are very pricey. Does anyone know of hq performance plugs best for a 5.4?

 

Only with modified engines. There is nothing wrong with stock Motorcrafts.

 

x2!
the factory motorcrafts are the best plugs you can run in the stock modular engines.

 

Save your money and get the Motorcrafts. The performance plugs are for super charged engines or highly modified engines.

 

To give you an idea, Troyer sells Denso Iridiums as part of their ignition upgrade kits and by themselves. If you are highly modded and/or tuned, they are a very good bet. They are not cheap but they are excellent. He sells IT16's through IT24's.