Originally Posted by tao3
Thanks everyboby for their help I understand now (wish it was written somewhere
The numbers and characters on the plugs, are the product number, wire thickness, and thermal range of the plugs body. Example: The Picco 7TH or
Wire Thickness: 7
Plug Type: T (Turbo)
Thermal Range: C = Cold, H = Hot. In Italian it would be F(fredda) = cold, and C (calda) = Hot
The plugs with cold thermal range, have a body with thinner walls and shorter body, so they dissipate heat better and faster to the engine head. The plugs with hot thermal range, have a body with thicker walls and longer body, so they retain heat and dissipate heat slower to the engine head. The number of threads is the same on both types of plugs.
How to select the proper plug:
When the ambient temperature is high, we have to use a plug with thicker wire.
With higher compression, we have to use a plug with thicker wire.
Humidity determines if we use a Cold thermal range, or Hot thermal range.
With high humidity percentage we should use a Hot thermal range plug.
If we have high temperature and high humidity, we should use a plug with thick wire and a Hot thermal range.
The best instrument to determine which Turbo Plug to use, are those digital weather stations, that have Temperature, and Humidity. That is the key to success or failure tuning engines with Turbo Glow Plugs, because they are so sensitive to weather variations that is unbelievable.