How to Choose the Right Glow Plug
The glow plug for your engine is the one that gives you the best performance. And you can choose the right plug for any situation, just by following the guidelines below.
1. Engine Type
Guideline 1: Know what type of engine you have. Is it a standard - or a turbo ?
Standard engines (engines with a 1-piece head) are most common. Standard plugs are easily available, inexpensive and fit almost all standard engines. Standard plugs are installed with a washer, which creates a compression seal with the head.
Many new O.S. engines are turbo engines, which feature a special 2-piece turbo head. The biggest benefit of turbo plugs is superior performance. Unlike standard plugs, turbo plugs (identified by a "P" in the description) feature a tapered "seat" that matches perfectly with the head. That creates a superior compression seal and with it, maximum efficiency and power. Turbo plugs are the choice for racers who want - and need - top performance.
A word of caution: you should never install a turbo plug in a standard engine or vice versa. Doing so risks doing serious (and expensive!) damage.

2. Displacement
Size matters to glow plugs. What size is your engine? A .12? .15? .21? Big engines have more mass and retain heat better. Smaller, lighter engines dont, and need the help a hotter plug can offer.
Guideline 2: The smaller the engine, the hotter the plug.