how many hp will KN air filter give the 4.3 eng

 

Just a panel filter (drop-in) won't gain you much if anything noticable (other than a placebo effect - "I spent money therefore it increased my HP). Now the K&N FIPK may net you 10HP under ideal conditions, but at $200+, it's pretty expensive.

Both will free up the intake and allow the engine to run more efficiently.