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Why do truck engines "need" hot glowplugs?

Why do truck engines "need" hot glowplugs?

Old 07-24-2017, 06:43 PM
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Default Why do truck engines "need" hot glowplugs?

Generally speaking I run medium glowplugs in all my nitro engines, the sole exception being my one engine that's tuned for winter use -- in that one engine I need a hot glowplug to offset the ignition delay caused by the cold ambient temperatures. But when I look at manufacturer websites, I see cold plugs listed for on-road cars, medium plugs listed for general use, and hot plugs listed for off-road trucks. I would've thought hot and cold would be the other way around, because my off-road trucks run at full-throttle under heavy load much more of the time than my on-road engines, and they don't need any help retaining enough heat to achieve proper ignition timing. On the other hand, the only time my on-road engines run at full-throttle is when they're at or near redline, where a hotter plug may be more useful for initiating combustion early enough that the burn can finish before the piston starts descending again.

What am I missing here? What is it about truck engines, whether their design or their usage, that makes them "need" hot glowplugs?
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Old 07-25-2017, 02:34 AM
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It is a bit of a wrong explenation.

The right plug is determed with the design of the engine. The compression, amount nitro and the glowplug determ the ignition timing (with a small influence by the weather). Many RTR engines are made to use hot plugs because they do make the engine run and tune more reliable. But a higher compression with a colder plug will run the engine more powerfull but it comes also with more wear on the internal components.
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Old 07-25-2017, 04:09 PM
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Yes, I understand those things affect ignition timing. However, fuel mixture also affects ignition timing; during the compression phase, a lean mixture will reach spontaneous-combustion temperature sooner than a rich mixture will, because more energy is required to heat more fuel. My off-road trucks tend to run richer mixtures because the engines have to work harder and there isn't as much wind to cool them down, so they need richer mixtures to keep them from overheating. In the past I haven't compensated for this at all. Should I be running hot plugs in my truck engines to compensate for the richer fuel mixtures, to achieve better ignition timing? Or is it irrelevant as long as the engines aren't obviously struggling to rev-up?
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Old 07-25-2017, 04:32 PM
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A hotter plug will give an easier combustion with a richer mixture, colder plugs can cause a flame out. On the other hand if you know how to tune an engine right you can make any configuration work as long the plug, head clearance and nitro content are set to each other.
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Old 07-25-2017, 04:33 PM
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Originally Posted by Roelof View Post
A hotter plug will give an easier combustion with a richer mixture, colder plugs can cause a flame out. On the other hand if you know how to tune an engine right you can make any configuration work as long the plug, head clearance and nitro content are set to each other.
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Old 07-25-2017, 04:57 PM
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Work well enough to run, perhaps, but not necessarily work optimally. There must be a "best" configuration for a specific engine running in a specific type of terrain during specific weather conditions, but I suppose that's a huge can of worms and figuring out all the possibilities would require an entire forum for just that one topic.

So it sounds like I should at least *try* hot plugs in my off-road engines to see if they suddenly unlock a bunch of extra power. I can do that.

A related question: Will a colder plug last longer in the same engine than a hotter plug? I would assume so, because colder plugs have thicker filaments, but maybe there's another factor I'm not considering. I ask because I have a couple off-road engines that I'm satisfied with their current power output, and I'm wondering if switching to hotter plugs to get more power would make me need to replace glowplugs more often.
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Old 07-25-2017, 05:15 PM
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If you stick with the manufacturer head clearance, plug advise and nitro content advise you can not go wrong. Making huge changes to one of them tou must compensate the ignition timing with one of the others to get it at the right moment again.

So if your motor is advised to run 25% with a medium/cold plug, lets say a nr5 plug and you want to run a nr3 plug, it cwould be wise to add a 0.1mm headshim.
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Old 07-25-2017, 09:51 PM
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I run 30% nitro in all my engines, because the extra oxygen content makes the engines run more consistently in the wide range of weather where I live. As a result, I can never run my engines with completely stock settings -- but that's okay, tinkering is part of the fun for me.
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Old 07-26-2017, 01:59 AM
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Originally Posted by fyrstormer View Post
I can never run my engines with completely stock settings
Stock settings? As in the manufacturer setting?
That is no ideal setting, that is just a starting point to get the motor fired up.
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Old 07-26-2017, 04:15 PM
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Yes, I know. None of my engines run the factory settings -- in fact, none of them would even start using the factory settings.
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