well my car seems to be laggin lately. It seems that theres no power below vtec but when it hits 4500 rpm it just have a surge of power. i had the same problem before but after valve adjustment, i fixed it a little bit. now its coming back and i just adjust my valves. What seems to be the problem here?

Also i was wondering how much horses would you lose having a cheap old spark plug? i think my car is misfiring but i dont know how much horses im losing. Any dyno would be cool.