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How to Choose the Right Glow Plug |
How a glow plug works.Spark plugs in gasoline engines cause ignition with a spark. In nitro engines, glow plugs cause ignition with heat. Heat is created initially by connecting a glow starter or 1.5V battery to the plug. Once the plug comes up to heat, the battery is disconnected and the heat retained by the combustion chamber will keep the engine running. Engine timing is automatic and controlled by engine rpm. Running at higher rpm makes the plug hotter and "fire" the fuel-air mix sooner. At lower rpm, the filament cools and the plug fires less frequently. |
The "right" 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.
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.
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 don't, and need the help a hotter plug can offer.
Guideline 2: The smaller the engine, the hotter the plug.
What's the nitro percentage in your fuel? High-nitro fuels produce more power than low-nitro fuels, but also produce more heat.
Guideline 3: The higher the nitro content, the colder the plug.
Smart modelers tend to keep a variety of glow plugs on hand. The reason? Because the "right" plug for your engine can change with the temperature. To achieve top performance, your choice of plug needs to change, too.
Guideline 5: The hotter the day, the colder the plug.
Here are a few other things you should know.
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.
Where you run also plays a part. If the track/course has a lot of twists and turns, a hot plug is fine. If the track/course has long straights where you'll reach maximum rpm, a colder plug is best.
Fuel-air mix not only affects how your engine performs; it can also have an impact on how long your plug lasts. If you run rich, it means that you're using more fuel than necessary for top performance. Modelers are often advised to run rich during engine break-in, because it helps cool the engine. However, running too rich can also cause an engine to "bog down" or quit entirely. In addition, it also means that the glow element is being exposed to more contaminants than necessary, which shortens plug life.
Running lean means that you're using less fuel. "Leaning down" an engine has a positive effect on performance. However, care is needed here, because over-leaning an engine can harm it, by raising operating temperatures, "burn up" a plug before its time.