razzor
05-23-2008, 02:26 PM
IT has come to my attention that I have never really addressed another mystery... “GLOW PLUGS"
What plug do you use for what engine? what plugs suit what conditions ?, What’s a good plug for my fuel ?
Ill is addressing these questions briefly and simply.
OK the plug acts obviously as an ignition system that is called “an energy perpetuated ignition system" meaning that every bang and spark generates heat and keeps the plug coil hot. So really we are relying on this unassisted ignition to keep our engines going... it’s no wonder they flame from time to time. It’s a delicate balance ...
OK so let’s do a simple test
Start your engine and leave the igniter on the plug. Let it run for about a minute to warm up. Listen to the idle and take off the igniter. What happened? If you noticed the idle drop then there is a good chance your plug is too cool! (Provided the engine is tuned properly) What’s happened is the energy from the igniter was removed and cooled the plug retarding the ignition. It could also mean you are running rich... you’ll have to determine which one... Massive!
This is one simple test to do.
But a rule of thumb you can all follow is the following
less nitro = Hotter Plug
More Nitro = Cooler Plug
So lets look at the Rossi range of plugs, because they are easy to follow... with low nitro you would use a # 5 plug say 15% 15 to 20% use a #6 (slightly warmer) 25 to 30 % nitro use a #7.. Besides the cooler plug retarding the ignition slightly it also has another purpose. Cooler plugs generally have a thicker element; the thicker element is also more resilient to higher impact explosions made by higher nitro. But in my opinion I always like to use a med to hot plug no matter what, cool plugs just don’t work for me... some people do like them but i dont.
Advantages of warmer plugs are they idle better and are harder to flame out.
Disadvantage they are a little more fragile...
Does the heat range of the plug make the engine run at a different temp? No it makes no difference except for one thing, a hotter plug will in most cases let an engine run harder therefore running hotter. It would seem the plug makes the engine hotter but its not, its like running a body without ventilation, it makes the engine run hotter but the body causes the symptom because it has changed a determining parameter... (I hope that makes sense
Ok now long body and short body plugs.
Simple really a short body plug increases geometric dome size reducing compression. A long body does the opposite; it reduces geometric dome size increasing compression.
So long body = better power = hotter engine
Short body = Less performance = cooler engine
Ahaaaa! You said the plug makes no difference to the temps! Well the heat range of the plug doesn’t but the physicality of its dimensions does. Its + or - a determining factor of how the engine runs. But all this is untrue really...... WHAT? ....
What’s really happening is a higher geometric compression will increase heat conductivity to the head button and release heat transfer via the heat sink more efficiently thus giving the impression the engine is running hotter for all you temp gun freaks out there... The reverse is true when you decrease geometric compression. This also applies to reducing head clearance; the engine will transfer more to the head as opposed to through the side walls and pipe. Remember the head button is aluminium and ally likes to absorb heat and dissipate it usually toward a cooler direction, towards a cooling head...
Confused? Don’t be, if we were to analyse how the brain works I am sure some of us, including me would get head aches... lol
Hope this helps in choosing plugs
source AFM
What plug do you use for what engine? what plugs suit what conditions ?, What’s a good plug for my fuel ?
Ill is addressing these questions briefly and simply.
OK the plug acts obviously as an ignition system that is called “an energy perpetuated ignition system" meaning that every bang and spark generates heat and keeps the plug coil hot. So really we are relying on this unassisted ignition to keep our engines going... it’s no wonder they flame from time to time. It’s a delicate balance ...
OK so let’s do a simple test
Start your engine and leave the igniter on the plug. Let it run for about a minute to warm up. Listen to the idle and take off the igniter. What happened? If you noticed the idle drop then there is a good chance your plug is too cool! (Provided the engine is tuned properly) What’s happened is the energy from the igniter was removed and cooled the plug retarding the ignition. It could also mean you are running rich... you’ll have to determine which one... Massive!
This is one simple test to do.
But a rule of thumb you can all follow is the following
less nitro = Hotter Plug
More Nitro = Cooler Plug
So lets look at the Rossi range of plugs, because they are easy to follow... with low nitro you would use a # 5 plug say 15% 15 to 20% use a #6 (slightly warmer) 25 to 30 % nitro use a #7.. Besides the cooler plug retarding the ignition slightly it also has another purpose. Cooler plugs generally have a thicker element; the thicker element is also more resilient to higher impact explosions made by higher nitro. But in my opinion I always like to use a med to hot plug no matter what, cool plugs just don’t work for me... some people do like them but i dont.
Advantages of warmer plugs are they idle better and are harder to flame out.
Disadvantage they are a little more fragile...
Does the heat range of the plug make the engine run at a different temp? No it makes no difference except for one thing, a hotter plug will in most cases let an engine run harder therefore running hotter. It would seem the plug makes the engine hotter but its not, its like running a body without ventilation, it makes the engine run hotter but the body causes the symptom because it has changed a determining parameter... (I hope that makes sense
Ok now long body and short body plugs.
Simple really a short body plug increases geometric dome size reducing compression. A long body does the opposite; it reduces geometric dome size increasing compression.
So long body = better power = hotter engine
Short body = Less performance = cooler engine
Ahaaaa! You said the plug makes no difference to the temps! Well the heat range of the plug doesn’t but the physicality of its dimensions does. Its + or - a determining factor of how the engine runs. But all this is untrue really...... WHAT? ....
What’s really happening is a higher geometric compression will increase heat conductivity to the head button and release heat transfer via the heat sink more efficiently thus giving the impression the engine is running hotter for all you temp gun freaks out there... The reverse is true when you decrease geometric compression. This also applies to reducing head clearance; the engine will transfer more to the head as opposed to through the side walls and pipe. Remember the head button is aluminium and ally likes to absorb heat and dissipate it usually toward a cooler direction, towards a cooling head...
Confused? Don’t be, if we were to analyse how the brain works I am sure some of us, including me would get head aches... lol
Hope this helps in choosing plugs
source AFM