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Old 07-26-2007, 10:10 AM   #1
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Default How does glow plug temps affect an engine?

I read on another thread about someone having an issue with idling and how a hotter plug may help.

Can someone go into detail how going to a hotter or colder plug affects an engine assuming fuel type stays constant?

Also, some detail on using a hotter / colder plug when changing fuel type (ie- more / less nitro).

What I am running if this helps is Byrons 25% race fuel, an OS VG .21 engine, previously using the stock OS Plug (what exactly is it?) and went to an MC8 so I am curious if that started my idling issue.
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Old 07-26-2007, 11:54 AM   #2
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Hot plugs give better idle and bottom end. This is because the element is thinner and glows hotter. Cold plugs give better top end the element is thicker and does glow as hot which doesnt idle as well but the thicker element is tougher and therefore can be run with leaner tuning.

Changes in fuel brand rarely require a change in plugs. However nitro content would have an effect. More nitro is like more oxygen so a richer mixture is required as nitro content goes up. The nitro content doesnt necessarily make it so you have to change pulgs either just engine tuning.
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Old 07-26-2007, 12:22 PM   #3
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this will help you choose a plug http://www.outlawrc.com/glowplugs.htm
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Old 07-26-2007, 12:38 PM   #4
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I believe the OS plugs are short plugs and the MC-8 is a long plug.
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Old 07-26-2007, 03:10 PM   #5
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my brother has a os 21rg and we use 20% byron ...
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Old 07-26-2007, 03:26 PM   #6
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I did notice that the OS plug was shorter than the MC8. The shim / washer supplied with the plug made it seem as if the overall gap would be the same.

What effect if any does having a long versus short plug do?
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Old 07-26-2007, 05:11 PM   #7
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On the not so bad situation, you will have the plug going into the combustion chamber, thus lessening its volume. This will increase the compression. So, you must be careful with what that can bring, like possible detonation.
On the bad situation, the piston will hit the plug, and that is bad!
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Old 07-26-2007, 09:26 PM   #8
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how many shims is everyone using when they go from an OS plug to a Mcoy plug?
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Old 07-26-2007, 10:08 PM   #9
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the best plug to run on that engine would be an os #8....
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Old 07-28-2007, 09:37 PM   #10
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Default A little more to it

You gotta think of the plug as one part of a two part system. Actually 3 parts. The fuel nitro % the head shims and the plug. Why you ask? Because they all contribute to the motor timing. Just like in any 1:1 motor these motors have to be properly timed to run properly. Since they are a diesel without a powered glow plug the compression of the motor the amount of platinum in the plug wire and the nitro % are all variables you have to balance out to get it to fire at the proper time. Decreasing shim thickness causes more compression and with the same plug and fuel % will result in advancing the timing. Putting more shim in will retard the timing. A hotter plug with the same shim thickness and fuel % will also advance the timing. Cooler retards the timing. For instance most manuals tell you to add shim when you go from 20 to 30% nitro. From the info above this would retard the timing which is the correct way to go since you are increasing the nitro and therefore advancing the timing. When the motor is timed properly the sound will be a percussive crack instead of a dull thud. If you aren't hearing that percussive crack you aren't even burning most of the nitro. Now you should understand why putting in a hotter plug will help with the idleing. You can probably achieve the same thing by getting rid of some shim. Most motors are overshimmed from the factory for safety margin. They don't want a lot of motors coming back from breakages during break in. Get yourself a deck height gauge or learn to do a deck height measurement with solder and a pair of calipers. Find out what the correct deck height is supposed to be for that particular motor and set that before messing with anything. Break it in first but set the deck height immediatly. You'll find if you get this set up properly you'll do a lot less tuning on the carb needles.

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Old 07-29-2007, 06:34 AM   #11
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What is the best plug for Hyper .21 8 ports turbo?
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Old 07-29-2007, 09:01 AM   #12
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Thanks for the info guys, this will be most helpful if I do nitro again in the future.
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