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Plug Too Hot #3022098
03/08/22 09:23 PM
03/08/22 09:23 PM
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Kentucky
clovis Offline OP
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Had our first test and tune last Saturday, car was a little sluggish. I had decided to move from an Autolite 85 to an NGK XR5. I’m running a 906 with about 9.5 to 1 compression. I run 90 no ethanol gas with a little Boostane, which is where some of the orange comes in on the plugs, should put me around 95 octane. . I was making some jetting and timing changes during the day with some success but after pulling some plugs I begin to wonder if the plugs were too hot. When I got home I looked my plugs with an otoscope and determined that there were black spots on the porcelain so denotation appears to be happening. My question is, is it due to timing or the plug or both. I bought some AR73 and was thinking of moving the timing back to 38 and re-start from there.

These are three different plugs at different timing. The car has always seemed to favor high timing, around 40 and there are times when 42 shows a pick up.

Anyway just looking for feedback and a recommendation.

7D56CFB4-DE62-4CD1-A929-D2AF95B39EDF.jpegE578E59B-1829-4A98-8B00-4ED5BC8A4389.jpeg90565D00-EB8A-4A67-BECA-BDECA8C16943.jpeg

'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119

"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
Re: Plug Too Hot [Re: clovis] #3022177
03/09/22 12:58 AM
03/09/22 12:58 AM
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Jeremiah Offline
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I run a ngk heat range 7 with a non projected tip. B7S.

I also ran a set of ngk R5670-7 which are prjexted tip. They used to ve axailable from heat ranges 4-9.



Re: Plug Too Hot [Re: clovis] #3022200
03/09/22 02:46 AM
03/09/22 02:46 AM
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Which type motor and total ignition timing are you tuning with, on?
Iron headed BB or?
the second and third plug pictures look good up
The first darker one not so much twocents

Last edited by Cab_Burge; 03/09/22 02:47 AM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Plug Too Hot [Re: Cab_Burge] #3022209
03/09/22 07:57 AM
03/09/22 07:57 AM
Joined: Mar 2008
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Kentucky
clovis Offline OP
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Cab, its a 383 with 906 heads. I am normally running anywhere from 38-40 degrees of timing. I have a Unilite distributor locked out with a MSD digital 6, so it retards 20 degrees while starting. Last year the more timing I put in it the faster it went, Saturday however when I started up on timing it slowed down and I can see the denotation specks on the porcelain, so just trying to decide if those XR5 are too hot or if I simply need to bring the timing down or both.


'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119

"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
Re: Plug Too Hot [Re: clovis] #3022212
03/09/22 08:19 AM
03/09/22 08:19 AM
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lewtot184 Offline
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looking at the pics i'd say there may be a manifold distribution issue or need for jet stagger. i don't see heat. i think maybe i'd keep the timing to around 38 degrees looking at the straps. those xr5's are close to the 85 or a j12y in heat range. carb/manifold specs would help.

Last edited by lewtot184; 03/09/22 08:20 AM.
Re: Plug Too Hot [Re: lewtot184] #3022229
03/09/22 09:41 AM
03/09/22 09:41 AM
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madscientist Offline
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Black specs are not detonation. Look at the inside of the shell and see how much carbon is built up on it. As a general rule, those black specs are bits of carbon coming off the shell and landing on the porcelain.

At your compression ratio you shouldn’t need any octane booster. There ain’t any power in octane and you only need enough octane to stay out of detonation. 91 pump gas should be more than enough.

EDIT: lewtot184 pretty much nailed it. Just wanted to add that. You always have to tune to the leanest cylinder but anything you can do to clean up what distribution issues you may have will always make more power and the engine will “drive” better.

Last edited by madscientist; 03/09/22 09:43 AM.

Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Plug Too Hot [Re: clovis] #3022289
03/09/22 12:08 PM
03/09/22 12:08 PM
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I would put the next colder plug in it based on the heat transfer onto the top thread only, it should be between 2 and 3 full threads is what I have been told a long time ago and retard the timing down to 34 to 36 degrees total BTDC. up
Have you verified that the zero mark on the dampener is exactly dead on at Top dead center?
If not, you should: scope wrench:

Last edited by Cab_Burge; 03/09/22 12:10 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Plug Too Hot [Re: Cab_Burge] #3022365
03/09/22 03:12 PM
03/09/22 03:12 PM
Joined: Mar 2008
Posts: 549
Kentucky
clovis Offline OP
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I am using a Victor 383 intake with a one inch 4 hole spacer, Demon RS carb with 1.50 venturi/1.75 base plate with an annular booster. I should have clarified the plugs are all from #1 on three different passes and were new before the pass.

There is very little carbon build up on the interior of plug where the porcelain is. When I look at the plugs under the scope you can see the black specs are only on one side of the plug. If the specks were coming from the interior would they be more uniform around the porcelain?

I guess I was thinking about the heat on the threads backwards, as I thought with it only impacting the top thread the plug was not too hot but maybe too cold, and is one of the reasons I posted.
It is the same for me with the strap, I have to remember it goes from the tip back, so when it is at the bottom close to the ring there is plenty of heat there. When I look inside the plug with the scope you can see where the heat has actually penetrated down inside the plug where the strap is attached.


'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119

"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
Re: Plug Too Hot [Re: clovis] #3022381
03/09/22 04:01 PM
03/09/22 04:01 PM
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Originally Posted by clovis
I am using a Victor 383 intake with a one inch 4 hole spacer, Demon RS carb with 1.50 venturi/1.75 base plate with an annular booster. I should have clarified the plugs are all from #1 on three different passes and were new before the pass.

There is very little carbon build up on the interior of plug where the porcelain is. When I look at the plugs under the scope you can see the black specs are only on one side of the plug. If the specks were coming from the interior would they be more uniform around the porcelain?

I guess I was thinking about the heat on the threads backwards, as I thought with it only impacting the top thread the plug was not too hot but maybe too cold, and is one of the reasons I posted.
It is the same for me with the strap, I have to remember it goes from the tip back, so when it is at the bottom close to the ring there is plenty of heat there. When I look inside the plug with the scope you can see where the heat has actually penetrated down inside the plug where the strap is attached.





Black specs are usually not detonation. Look at them closer. If they are shiny and/or purple looking that’s detonation. It doesn’t take much carbon to leave those specs.

Your ignition box is retarding with RPM. They all do it, and they don’t all do it the same. You should never lock out a distributor. Find someone with a distributor machine that knows how to use it and send them the box, distributor and coil and have them test it and correct for the retard.

A hotter plug will show more heat in the threads.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Plug Too Hot [Re: madscientist] #3022396
03/09/22 04:37 PM
03/09/22 04:37 PM
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i think the strap is showing too much timing. how much camshaft? i'm not much into the locked ignition thing but there is a place for it, and in my opinion that is when the vacuum is so low you loose control of the carb at low rpm. i think some folks use locked ignitions as a way to make up for their lack of knowledge in setting up an ignition curve.

Re: Plug Too Hot [Re: lewtot184] #3022504
03/09/22 10:27 PM
03/09/22 10:27 PM
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Kentucky
clovis Offline OP
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The camshaft is a comp 6329 solid 252@.050 about .580 lift with a 1.6 rocker.

What is the down side to locking out the distributor?
My distributor adds 24* of mechancial advance, so the motor likes at least 20 degrees at idle so that was pushing me over 40, so we made the decision to just lock it out.

So the plug heat range seems ok to everyone and i just need to come down on the timing?


'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119

"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
Re: Plug Too Hot [Re: clovis] #3022537
03/10/22 01:20 AM
03/10/22 01:20 AM
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Shorten the slots so you get 34 total. You could send to a shop or have one built or YouTube how to make it happen. I found a 383 in typical ky weather during the summer on 93 octane ran choppy on 38 total, little better on 36, and smooth as silk on 34. The 38 total got about 1/2 a mpg better, but felt all wrong. I think it pinged and it couldn’t be heard, got lots of popping in the exhaust on decel. Just not happy. Kept backing down and running same loop until it felt free and fast. I didn’t track that car so no idea what those changes netted out, but it had more zip with less timing. I think the strap is showing it firing way down the side and not at the tip.

You run clay city?


I want my fair share
Re: Plug Too Hot [Re: clovis] #3022565
03/10/22 10:01 AM
03/10/22 10:01 AM
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Originally Posted by clovis
The camshaft is a comp 6329 solid 252@.050 about .580 lift with a 1.6 rocker.

What is the down side to locking out the distributor?
My distributor adds 24* of mechancial advance, so the motor likes at least 20 degrees at idle so that was pushing me over 40, so we made the decision to just lock it out.

So the plug heat range seems ok to everyone and i just need to come down on the timing?


As I stated above, all ignition boxes retard with RPM. All of them. They don’t all retard at the same RPM or the same amount but they all do it.

Let’s say your box starts retarding at 4K and it’s losing 2 degrees. By 5k, it loses another degree and at 6k 2 more degrees. That’s a total of 5 degrees. Most engines don’t like a 5 degree change in ignition timing.

As lewtot said above a locked out distributor is mostly done because guys don’t know how to get the correct curve or maybe they don’t care. But mostly I think guys just don’t know. I know I didn’t. And I was locking out distributors for 25 years. And because of THIS forum and the one guy on here who said all ignition boxes retard (and he wasn’t wrong) I went out and bought a distributor machine so I could test what he said. And like I said, he was right on the money and I was DEAD wrong.

His name is William Baldwin. A very smart man.

I was appalled when I found out how much some of these boxes retard.

If you are getting 24 degrees of mechanical advance at the crank, it means your distributor has 12 degrees in it. You double whats in the distributor to get what you see at the crank.

With the correct curve and a proper tune up, those factory iron heads will want about 38-40 degrees total. BTW, keep in mind that a timing light is electronic, that it has a slew rate (speed of the electronic switches which is what retards the timing in the boxes) and that they don’t all read the same either. But as a general rule, you should be at 38-40 total with those heads. Your light could be off a degree or two, or maybe even more. So always use the same timing light and look at your plugs and let them tell you what your timing should be.

So...for what you have and to get 20 initial and let’s just say 38 total you only need 18 degrees of mechanical advance in the distributor. Which means you only need 9 degrees in that advance in distributor degrees. Right now, if you have 24 on the crank (mechanical advance) you have 12 degrees in the distributor. You need take 3-4 degree out. I would shoot for 8 degrees in the distributor and let it run at 21 initial.

Then for the curve I’d need more information. But I’d delay the curve starting until 2000-2200 and get it all in by 3800 or so. That may change a bit if you have vacuum advance.

Just my .02 cents. BTW, on pump gas the total timing Mark can be right at the shell.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Plug Too Hot [Re: madscientist] #3022665
03/10/22 03:47 PM
03/10/22 03:47 PM
Joined: Mar 2008
Posts: 549
Kentucky
clovis Offline OP
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Mad

Very good information and maybe we need to talk off-line but for the sake of education to me and others I'll keep this thread going.

Again, you'll have to remember I'm an accountant, so I have experience with only three engines, and those are the ones that have been in my car, so like you said I have learned a lot from this site and come here often to ask questions and seek knowledge. Also as an accountant I like keeping and analyzing data. In looking at my data, I would say that the car likes more timing early, my best 60 fts are with the distributor locked out at 40*. I have also read that an engine doesn't need as much timing at higher rpms (so the boxes building in a retard function as rpms go up seems like a good thing), so what happens in a distributor seems almost backwards to what a performance engine would want. This is where is I have to ask the question, is a curve moving from low to high actually a good thing? Assuming box reduction, with a non-locked out distributor your curve would be 21 to 40 to 35, with it locked out it would be 40 to 35. When I compare all the measurement points (60, 330, etc.) and look at the plugs the cars seems quicker, faster and happier with a non-curved distributor. Now the second question, could it be faster with a different curve that has different initial and ramped in timing? and how do I get there? I love to test and tinker so I am wiling to be guided down a path here.

Thanks again for the input, I enjoy the mental exercise.


'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119

"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
Re: Plug Too Hot [Re: clovis] #3022679
03/10/22 04:32 PM
03/10/22 04:32 PM
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Originally Posted by clovis
Mad

Very good information and maybe we need to talk off-line but for the sake of education to me and others I'll keep this thread going.

Again, you'll have to remember I'm an accountant, so I have experience with only three engines, and those are the ones that have been in my car, so like you said I have learned a lot from this site and come here often to ask questions and seek knowledge. Also as an accountant I like keeping and analyzing data. In looking at my data, I would say that the car likes more timing early, my best 60 fts are with the distributor locked out at 40*. I have also read that an engine doesn't need as much timing at higher rpms (so the boxes building in a retard function as rpms go up seems like a good thing), so what happens in a distributor seems almost backwards to what a performance engine would want. This is where is I have to ask the question, is a curve moving from low to high actually a good thing? Assuming box reduction, with a non-locked out distributor your curve would be 21 to 40 to 35, with it locked out it would be 40 to 35. When I compare all the measurement points (60, 330, etc.) and look at the plugs the cars seems quicker, faster and happier with a non-curved distributor. Now the second question, could it be faster with a different curve that has different initial and ramped in timing? and how do I get there? I love to test and tinker so I am wiling to be guided down a path here.

Thanks again for the input, I enjoy the mental exercise.




You can set it up for more initial if you think you think you need it. You just need to reduce the amount of mechanical advance the distributor has. At this point, converter stall speed needs to be considered and even your starting line ratio. And then we need to know when and how much your box retards so that can be corrected with the curve.

Of course, this all affects your carb tune up too.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston






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