416 scamp
Well-Known Member
What plugs would you guys recommend for my 12to1 416? I was told to go to a colder plug with that comp. Right now im running champion RC12YC. Any ideas would be appreciated.
what plugs?
- Thread starter 416 scamp
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The best way to know is to read the plugs after you have run them. Pull a plug and look at the threads. You should see the last 2 threads looking dull and the rest shiny. If too many are dull the plug is too hot. If there is only 1 or no threads dull it is too cold. Reading plugs is an invaluable and often overlooked science that can tell you pretty much everything you need to know including whether or not your timing and air/fuel mixture are correct. Of course, having an oil leak just screws this all up.
GoodysGotaCuda
Mr. Goody
Sorry for jumping in. But if it is too cold, what are the side effects to the motor? Will it run harder with a hotter plug? Will too cold cause pre-ignition or something else?
3
340srule
Guest
ngk race 10's.......
mullinax95
Well-Known Member
This might help you: http://www.usaimports.co.uk/Mopar_Tech_Pages/Spark_Plug_Reading.htm
416 scamp
Well-Known Member
Thanks guys :thumbup:
mullinax95 said:
Ah, at first I thought they had stolen that from FBO's excellent site but they are actually working with them. There is a link to FBO on this Forum. They have a good rep and a lot of good info on their site. That page goes into detail about reading your plugs and all of the info is dead-on correct.
340mopar
Sorgermotorsports
Changing the heat range of a plug does not change how well the fuel is burned. The heat range of a plug is related to how well it transfers heat from the tip to the body of the plug then cylinder head. A hotter plug has a longer electrode tip so it keeps the tip hot enough to keep it clean. A colder plug has a shorter tip so it transfers heat easier to the plug body then to the head so it runs cooler in the same given motor. It is recommened as a general rule that with every 75 - 100 change in horsepower you run one step colder plug. The reason is that a higher HP motor will generate more heat and will overheat a "stock" heat range plug. The colder plug will allow the plug tip to run at the correct heat level without overheating it.
Like stated earlier too hot of a plug can cause engine damage from detonation. If you use too cold of a plug the plug tip won't get to the right heat level to keep it clean so it will foul prematurely. So it is much better to start with too cold of a plug and work your way up until the fouling is minimized.
I run a plug 4 heat ranges colder in my 340 because I am at about 550hp.
Chuck
Like stated earlier too hot of a plug can cause engine damage from detonation. If you use too cold of a plug the plug tip won't get to the right heat level to keep it clean so it will foul prematurely. So it is much better to start with too cold of a plug and work your way up until the fouling is minimized.
I run a plug 4 heat ranges colder in my 340 because I am at about 550hp.
Chuck
AdamR
Big Member
I will have to check my notes but I think my 11:1 340 has Autolite 25s in it.
340mopar said:
No and yes. The premature fouling you mention is caused by the poor or incomplete burning of the fuel that I mentioned leaving deposits on the plug which is a result of the plug being too cold as I mentioned and not getting to the proper temp as you mentioned. What I said about too cold a plug affecting the burning of fuel was indeed correct as is what you said about the result. This is also true with a plug that is too hot which causes premature burning of the fuel so heat range (how well a plug dissipates heat, a plug does not generate heat) does indeed affect the burning of fuel. That is in fact part of it's purpose- to control the temperature at which the fuel is burning by dissipating some of that heat through itself to the head as you said. The optimum plug is the one that keeps the fuel burning at the temperature that results in the most efficient, i.e complete, burning of that particular fuel in that particular engine. If you change back and forth between pump gas and race gas you will have to run two different plugs depending on which gas you are running because they do not burn best at the same temperature. Pump gas burns hotter. That is why it is important for those of us who mix the two (as I do) to be consistant with the mix. Bottom line is that the best way to know which plug is best is to read the plugs. The "two thread" method I use is something I learned from a local MOPAR tech who has been building race engines since the 60's. FBO uses the same method in the article that mullinax95 posted. As you said, it is best to start too cold because that does not run the risk of damage that starting too hot does.
1qwikScamp
Well-Known Member
i switch between autolite 65 and 63 just depending on how it is running at the time
340mopar
Sorgermotorsports
2shelbys said:
Putting a hotter plug in a motor just because you fuel ratio is to rich or lean is not the correct way to find the correct heat range. In other words if your fuel to air ratio is wrong and you take a plug reading it won't be accurate. The cylinder pressure, fuel to air ratio and type of fuel used are the main contributors to combustion temperature. The spark plug is just that, a spark to ignite the mixture it does not regulate combustion temperaure. The method of going to one step colder plug with every 75 - 100 HP is right from the Mopar LA Engine manual. The length of the tip of the spark plug is to regulate it's own heat from the combustion of the fuel. Since motors can have hundreds of different type of combustion properties is the reason why there are 100's of different types of plugs and heat ranges. Too cold of a plug will fire the fuel the same as too hot a plug until it becomes fouled. It sounds like you are saying the minute you put the too cold of plug in it will misfire and incomplete burn the fuel and that is not true. It will fire the mixture fine up until it becomes fouled.
Let me explain it with a vehicle that you can relate with; a turbo car. If you have take a NA motor car with the correct air/fuel ratio then you put a turbo on this motor with the same correct air/fuel ratio you will have to go to a colder plug because of the higher HP which = higher combustion temperatures. Now take this turbo motor and give it a rich air/fuel ratio, now the car is fouling plugs. Do you put a hotter plug in it? although it might correct the fouling because of the lower combustion temperatures it is only a band-aid fix and the car is sluggish (lower HP) because of the over rich air/fuel ratio. The correct fix is to lean out the air/fuel ratio to the correct ratio. If the air/fuel ratio is now corrected and the motor is still fouling plugs then you need to start trying one step hotter plug at a time until you minimize the fouling.
Now let's throw a weak ignition into the equation and now it really throws off our plug reading scenario.
In summary if you have a dark colored plug it could be too rich a mixture, a weak ignition or too cold a plug. It would be wise to start with making sure the ignition is in good working order then check the air/fuel ratio then the heat range of the plug, not the plug heat range first. I not saying that you can't check the plug to see if it is too cold or too hot. It's that you can't check it until the other items are checked first or it won't be accurate.
Chuck
I didn't say anything about that.340mopar said:
Reading the plug will tell you that your air/fuel ratio is wrong. You are correct in that it does not regulate the temperature by itself but it is a contributing factor in how well the fuel burns as are several other things like those you mention.
I did not challenge or say anything about that but it is only a guidline to get you close to right. The best way to know you are right is not just doing what a book says, it is looking at the plugs a verifying that the combustion process is as efficient as possible.
We are saying the same thing in different ways. Too cold a plug will only fire the same briefly because it will become fouled. That fouling is the deposits left by inefficient burning of fuel.
No, nothing I said should make you think that. If the plug is WAY too cold it could happen that fast but not if you are only 1 or 2 steps too cold. The diffference between heat ranges is not that night and day, it is very subtle. I believe the difference from one range to the next is like 75° - 100° in heat dissipation ability.
No matter how you or I word it, the goal of all adjustments including which plug you run is to acheive the most efficient burning of fuel.
340mopar said:
Chuck you are explaining things that do not need to be explained and creating debate where there is none. I said nothing about changing plugs to correct air/fuel mixture nor did I say anything about checking heat range first. I specifically said that reading the plugs will tell you pretty much everything you need to know, proper heat range being only one of those things. You are assuming I see the plugs as a fix-all or temperature control which is not the case. And why would I relate better to a turbo car? I have only been running them for 20 years. I have been running V8's for almost 30.
What do you mean by "a dark colored plug"? You look to different areas of the plug for different things and it is not just the color but where the color appears that is telling. Read the article mullinax95 posted. It breaks it down very well.
340mopar
Sorgermotorsports
2shelbys I know what you meant on your previous posts and wasn't trying to put words in your mouth, as a matter of fact we really agree. The problem is your post was very general as stating that a too cold of a plug = misfiring and incomplete burned fuel. For a person that doesn't understand what you mean or how that would happen they might take it as a colder plug gives you less HP than a hotter plug and the misfiring would be instant and we both know it's not. There are lots of people on this site that are just learning about these things and leaving things out can be as bad as giving mis-information. You weren't mis-informing in your post you just didn't explain how this happens. I was trying to fill in the blanks and in the process I made you think I did not agree with you, this is not the case. Your statement about finding the correct plug for a particular set-up is spot on correct.
Chuck
Chuck
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