The extended tip plugs run cooler then the recessed tips. The tip is out in the comp. chamber & the gasses flowing by cools it. When the ext. tip came out in the 60's all the car cos. immediatly started useing them as original equip. Except on flatheads. The only reason the old manuals dont show them because they are reprints from the original. I have been useing ex. tip plugs for 50 years on every thing I have serviced except flatheads, & have never blown a piston.
