This is the Ultimate Engines. P4 "Super Hot" Turbo Glow Plug. Choosing the right glow plug is critical for peak engine performance and there are a number of different factors that will determine which plug you should use. Engine type, air–fuel mix, nitro percentage, and even air temperature are things that must be taken into consideration. What's more, the ideal glow plug choice will change as conditions change. Keeping a range of glow plugs on hand will help you fine–tune glow heat and enjoy maximum performance in all conditions.
Generally, Hot plugs promote better idling and acceleration. If your engine runs rough or accelerates sluggishly, a hotter plug will help. Cold plugs produce more power and may improve performance if your engine runs hot. The downside is rougher idling and more difficulty in tuning.