Have a hipo 283--little over 300 h.p.--time for a spark plug change--Had to replace the AC R45S plugs with NGK BR6S plugs last time because I couldn't find the AC's where I was at---ran fine but is the 45s teh way to go or just stick with the NGK--1.5 pistons and early power pack heads--had a plug problem on the road is why I have NGK in there now---is there a better heat range I should use--3.70 rear gears--not a whole lot of driving but high rpms at times---thanks