Appreciate some input on spark plug reading

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mderoy340 said:
The heads are probably the limiting factor if your tune is optimized. I go down one jet size in May and another one down in July when it really gets hot and humid. The higher the humidity the lower amount of oxygen available to burn. My car runs best @12.4 flat fuel curve with the O2 sensor I currently have on 93 pump. Most folks just run pig rich all summer and dial slower.
You are at the mercy of whatever the quality the fuel is on the day you fill up. WaWa 93 is what I've been using lately. Find a station that sells a lot of fuel. Race gas is always the same quality so keep that in mind.
- Make sure your carb is sealed to the hood scoop to prevent hot under hood air from entering.
- A return style fuel system will keep the fuel and carb cooler.
- A dash camera mounted to view the important gauges helps to review after the run. (poor man's data log)
You may also want to calculate the converter slippage at the stripe in third gear. Wallace racing has all the formulas for that.
Click to expand...
Forgot to add....
The torque conv slip calculates out to about 6%-7%. This is an 8" ATI TreeMaster converter that I ordered from them after discussing the engine with them. My original target was about 4700 stall but it actually stalls at 5000 (and I'm glad it does!). I shift the car at 6200 for both shifts and it traps right about that same rpm. When I shift (RMVB), the rpm pulls down to about 5500 and goes back up from there. I've been really happy with this conv as it seems quite tight on the street unless you stand on it. Example: in 88 degree heat driving to a cruise/show on Friday, the trans was at 165F after 22 miles. Pretty good if you ask me!
 
Demonx2 said:
Forgot to add....
The torque conv slip calculates out to about 6%-7%. This is an 8" ATI TreeMaster converter that I ordered from them after discussing the engine with them. My original target was about 4700 stall but it actually stalls at 5000 (and I'm glad it does!). I shift the car at 6200 for both shifts and it traps right about that same rpm. When I shift (RMVB), the rpm pulls down to about 5500 and goes back up from there. I've been really happy with this conv as it seems quite tight on the street unless you stand on it. Example: in 88 degree heat driving to a cruise/show on Friday, the trans was at 165F after 22 miles. Pretty good if you ask me!
Click to expand...
A street strip setup is a compromise. My 10" 3400 is to tight for my 360.
This camera is less than a go pro and works great.
https://www.amazon.com/AKASO-EK7000-Sports-Waterproof-Camcorder/dp/B01HGM33HG/?tag=fabo03-20
 
Hysteric said:
All stuff to try when looking to improve combustion......

How to Pick the Best Carburetor for a Street/Strip Car

Have to laugh when the smaller carb ran quickest and idles best its 425 CI on street fuel:

As you can see from the Dragstrip Test Results chart, our guess that the 650 carburetor might run the quickest of the bunch turned out to have some validity. The smaller carburetor delivered the quickest move to the 330-foot mark and the quickest overall e.t. and fastest mph

I wonder what that's telling you this engine needs......what does the smaller carb do?


It needs to use more of the fuel it already gets......
Click to expand...
I'm not saying that a smaller carb can't make a lower ET at the dragstrip but for me the test at the dragstrip they used to confirm this was not conclusive proof. There may be better test out there to use as evidence.

The article is written in a way to make you believe that the reason the car went faster was because of the difference in size of the carburetors. This was stated at the beginning of the article. Maybe this was just hindsight or maybe it was a bit of confirmation bias.

There were many differences in the carburetors. Some differences include choke horn vs no choke horn, downleg booster vs straight leg booster, differences in the emulsion packages, carbs with and without jet extensions, power valve package, carb bowl size, advertised cfm vs actual measured cfm, etc.

Without testing to control for the variables or even ABA testing to control for repeatability the conclusion reached could have also been that the cost difference of the carburetors was the reason for reduced et.

This isn't to say that the testing they did here is worthless but maybe incomplete. Sometimes there isn't enough time, money parts etc.to do the testing we would like to do so we do the best we can. It is at least entertaining to think that a smaller carb could out perform a larger carb. We as people love a small vs big story and a story that contradicts the conventional wisdom that bigger is better.

It's not surprising that a carb could be either too big or too small depending on what you goal is. Add to this multiple goals like fastest et and good street manners and you open another whole can of worms.
 
Last edited:
92b said:
I'm not saying that a smaller carb can't make a lower ET at the dragstrip but for me the test at the dragstrip they used to confirm this was not conclusive proof. There may be better test out there to use as evidence.

The article is written in a way to make you believe that the reason the car went faster was because of the difference in size of the carburetors. This was stated at the beginning of the article. Maybe this was just hindsight or maybe it was a bit of confirmation bias.

There were many differences in the carburetors. Some differences include choke horn vs no choke horn, downleg booster vs straight leg booster, differences in the emulsion packages, carbs with and without jet extensions, power valve package, carb bowl size, advertised cfm vs actual measured cfm, etc.

Without testing to control for the variables or even ABA testing to control for repeatability the conclusion reached could have also been that the cost difference of the carburetors was the reason for reduced et.

This isn't to say that the testing they did here is worthless but maybe incomplete. Sometimes there isn't enough time, money parts etc.to do the testing we would like to do so we do the best we can. It is at least entertaining to think that a smaller carb could out perform a larger carb. We as people love a small vs big story and a story that contradicts the conventional wisdom that bigger is better.

It's not surprising that a carb could be either too big or too small depending on what you goal is. Add to this multiple goals like fastest et and good street manners and you open another whole can of worms.
Click to expand...
The most telling factor is WOT Vacuum.
 
Demonx2 said:
Curious why you suggest a hotter plug? If I'm reading the ground strap correctly, I'm fairly tight on timing using pretty much the standard heat range plug as these AR3924 Autolite's compare to the old Champion RJ12YC's (or RC12YC's - you get the point!). The burned clean area goes around the corner of the strap and gets somewhat close to the threads. Maybe a degree or 2 could be added but surely no more. Why do you suggest a hotter plug? I was thinking if I'm going to try a bit of spark, perhaps try it with a 1-step colder plug.

I was with a friend yesterday that basically raced from the 60's through the 90's. Raced many cars in many classes. Even has a Wally! I had him look at my plugs and went through the discussion with him. His opinion was it looks just about right, perhaps a tad rich, if anything, but not too bad.

I could just be facing what Don (@B3422w5 ) suggested - that being just not enough port flow and/or cam for the 4" stroke.

Florida won't be getting any cooler as the months progress so it will be interesting to see what response, if any, I can get if I make a change. Oh, and the car did just make a 45-50 mile round trip to a local cruise Friday afternoon/evening. Not bad given the 90 deg temps!! Here it was parked with our friend's Petty blue 72 Demon 340. Cool!!
View attachment 1716239463
Click to expand...
alrighty
 
Demon,
Why do you think you may need a colder plug? When you have the correct heat range, do you know what the lower & higher temp limits are for for reliable spark delivery?
I can think of a couple of reasons to go hotter, not colder.
 
Bewy said:
Demon,
Why do you think you may need a colder plug? When you have the correct heat range, do you know what the lower & higher temp limits are for for reliable spark delivery?
I can think of a couple of reasons to go hotter, not colder.
Click to expand...
I don't think I necessarily need a colder plug but, if I want to add some spark, it should not hurt it either.

I worked for an OEM on engines my whole life. Always target to get the coldest plug that doesn't foul under the worst conditions, be it granny starts and drives or repeated cold starts at -20F. High cyl pressure (i.e. high power) engines use colder plugs (colder than production) for high speed/high load extended durability tests. You want to prevent any type of hot spot in the chamber - spark plug or otherwise.

Drag racing isn't exactly an extended test but it is certainly a high speed/high load test.
 
The problem with a colder plug to 'add some spark' is the risk that the plug is too cold to burn off the tip deposits in cruise/idle mode. It then misfires....right when you want max spark energy.
The object is to bring the tip temp to over 400* C & keep it there, where it self cleans; max temp should be 850* C, so there is a 400+* C [ 720* F ] working range.
 
Bewy said:
The problem with a colder plug to 'add some spark' is the risk that the plug is too cold to burn off the tip deposits in cruise/idle mode. It then misfires....right when you want max spark energy.
The object is to bring the tip temp to over 400* C & keep it there, where it self cleans; max temp should be 850* C, so there is a 400+* C [ 720* F ] working range.
Click to expand...
Yes, and the REAL problem is nobody runs all the tests to determine what these old engines really require given all of the mods done to them by each of us!
 
Demonx2 said:
Yes, and the REAL problem is nobody runs all the tests to determine what these old engines really require given all of the mods done to them by each of us!
Click to expand...
People do, you just never come across them.
 
Demonx2 said:
Well I just had to go pull the rest of the plugs and then cut one open. All 8 of the ground straps look the same - they are clean from the tip down to around 0.090-0.100 from the thread body (pics don't show it too well hence my measurements).

Here's a pic of the one I cut open (happens to be #6). Remember this is on pump 93 fuel.
View attachment 1716238516
View attachment 1716238522

It looks like the dark ring is a tad over 1/8" up from the insulator step. Also know this plug was not pulled at the end of the track but was essentially pulled after driving back to the pits and sticking the car in the trailer.

It should also be mentioned that all the plugs have roughly the bottom 2-3 threads showing darker/sooty.

So there we have it. Perhaps a tad in the rich side? Temps did climb throughout the day from 63 upon arrival to 87 when the last pass was made. And I didn't change any jets as I didn't need another variable! (The car ran 11.140 off the trailer at 63F (455 DA) and 11.162 on the last pass at 87F (1980 DA).
Click to expand...
Here is some info I found a while back. Read through it. Your plugs look pretty good to me overall>

When observing deposits on the sides of the center electrode.
The deposits here should only be light after a lot of miles on the engine. If the deposits
are building up with a few runs the plug is too cold. Deposits of any type here can cause
electrical conduction and wastage of some or all of the spark energy.
2- The strap or ground electrode
The projection of this into the cylinder is the most important factor to the combustion.
When the arc is too close to the head surface the arc occurs in the boundary layer gas.
When the arc is in the boundary layer it is not in fresh air. The boundary layer is not
effectively scavenged. Different combustion chamber design and valve seat angles
and different porting alters the scavenging of the boundary layer. The boundary layer
is possible to be.040" thick but that is unlikely in that part of the engine. But I have
gained 800rpm's of torque converter stall in some tune situations by projecting the
plug further into the chamber. The optimum arc location depends on the amount of
vaporization that occurs around the arc location. If the mixture distribution is
improved then the arc can be further out in the cylinder. The further out it can be used
the more power the engine makes because the flame kernel is able to grow in a more
spherical fashion and more molecules are engaged in early combustion. That greatly
increases the energy within the cylinder. When tuning to test projected arc locations it
is important to reduce the ignition timing first. And one must proceed carefully.
3- The outer surface of the porcelain near the roll at the top of the porcelain
and the flat section going across to the center electrode.
This area shows the coloration of the very first part of the flame kernel. It is a zone
that gives clues to the changing burn of the flame kernel during the time of electricity
duration.
4- The sides of the porcelain down to about 3/16th of an inch above the base of
the porcelain.
This is read in conjunction with the reading of #3. Changes in color between #3 and
#4 can be used as a gradient indicator of the burn style.
5- The base of the porcelain where it meets the metal area of the body including
about 3/16th" above that.
This never gets hot enough to alter or remove deposits. Dark grey is rich side of
stoichiometric and is the common colour aimed for with Holley style carburetion.
However tan is possible and usually occurs on high power per cubic inch cylinders.
Deposits formed here are due mainly to the lower heat input to the mixture, which is
because the base of the plug is cooled by the water jacket. The gas level present here
is greatly affected by the scavenging process. If the scavenge is inadequate to clear
gases from the base of the plug a few possible conditions can arise. The gas
composition present here after scavenge is important too. If the gas is predominantly
CO2 the resident gases could add heat to the incoming charge and assist vaporization
without adding a fuel gas to the mixture. If the gas is CO the mixture will be heated
less but a fuel gas will be present. CO has a very low heat output and it tends to create
a grey deposit. If the zone is effectively scavenged the heat must be sufficient to
vaporize the fuel to a sufficient gas state, if that’s not achieved yellows or greens
appear near the base. If sufficient vaporization is achieved then light deposits of tan
etc will appear.
6- The inner surface of the body of the plug that is exposed to the combustion
gases.
This indicates the effective cooling of the body by the water. The type of carbon
deposited here can vary a lot because of what style of burn is happening. Here you
can see the effect of water temperature on the vaporization, It is through experience at
looking at lots of engines and understanding their intricacies in various weather
conditions that you learn how water temperature affects combinations.
7- The threaded area.
The threads should never be exposed in the chamber. It is necessary to check the
thread length of the plug and to determine if any thread is exposed inside the
chamber. This must be done with the cylinder head removed from the engine. If any
thread is exposed to the chamber the temperature of the strap electrode will be raised
significantly. The strap electrode looses heat to the cylinder head via the transmission
path of the threads.
The threads that are engaged within the head can still get dark deposits on them. What
they indicate is the cylinder pressure. If the threads don’t show any signs at all of dark
creeping up the threads then the engine is a slug. A good engine will blow deposit
colouration up to 2 or even 3 threads.
 
A more 'scientific' approach to plug heat range might be to use what the car maker spent hours on testing & researching. Then look at your engine & see what has been changed that might require a change, if any, in heat range; do not just fit colder plugs because Billy fitted colder plugs to his engine....
 
71GSSDemon said:
Here is some info I found a while back. Read through it. Your plugs look pretty good to me overall>

When observing deposits on the sides of the center electrode.
The deposits here should only be light after a lot of miles on the engine. If the deposits
are building up with a few runs the plug is too cold. Deposits of any type here can cause
electrical conduction and wastage of some or all of the spark energy.
2- The strap or ground electrode
The projection of this into the cylinder is the most important factor to the combustion.
When the arc is too close to the head surface the arc occurs in the boundary layer gas.
When the arc is in the boundary layer it is not in fresh air. The boundary layer is not
effectively scavenged. Different combustion chamber design and valve seat angles
and different porting alters the scavenging of the boundary layer. The boundary layer
is possible to be.040" thick but that is unlikely in that part of the engine. But I have
gained 800rpm's of torque converter stall in some tune situations by projecting the
plug further into the chamber. The optimum arc location depends on the amount of
vaporization that occurs around the arc location. If the mixture distribution is
improved then the arc can be further out in the cylinder. The further out it can be used
the more power the engine makes because the flame kernel is able to grow in a more
spherical fashion and more molecules are engaged in early combustion. That greatly
increases the energy within the cylinder. When tuning to test projected arc locations it
is important to reduce the ignition timing first. And one must proceed carefully.
3- The outer surface of the porcelain near the roll at the top of the porcelain
and the flat section going across to the center electrode.
This area shows the coloration of the very first part of the flame kernel. It is a zone
that gives clues to the changing burn of the flame kernel during the time of electricity
duration.
4- The sides of the porcelain down to about 3/16th of an inch above the base of
the porcelain.
This is read in conjunction with the reading of #3. Changes in color between #3 and
#4 can be used as a gradient indicator of the burn style.
5- The base of the porcelain where it meets the metal area of the body including
about 3/16th" above that.
This never gets hot enough to alter or remove deposits. Dark grey is rich side of
stoichiometric and is the common colour aimed for with Holley style carburetion.
However tan is possible and usually occurs on high power per cubic inch cylinders.
Deposits formed here are due mainly to the lower heat input to the mixture, which is
because the base of the plug is cooled by the water jacket. The gas level present here
is greatly affected by the scavenging process. If the scavenge is inadequate to clear
gases from the base of the plug a few possible conditions can arise. The gas
composition present here after scavenge is important too. If the gas is predominantly
CO2 the resident gases could add heat to the incoming charge and assist vaporization
without adding a fuel gas to the mixture. If the gas is CO the mixture will be heated
less but a fuel gas will be present. CO has a very low heat output and it tends to create
a grey deposit. If the zone is effectively scavenged the heat must be sufficient to
vaporize the fuel to a sufficient gas state, if that’s not achieved yellows or greens
appear near the base. If sufficient vaporization is achieved then light deposits of tan
etc will appear.
6- The inner surface of the body of the plug that is exposed to the combustion
gases.
This indicates the effective cooling of the body by the water. The type of carbon
deposited here can vary a lot because of what style of burn is happening. Here you
can see the effect of water temperature on the vaporization, It is through experience at
looking at lots of engines and understanding their intricacies in various weather
conditions that you learn how water temperature affects combinations.
7- The threaded area.
The threads should never be exposed in the chamber. It is necessary to check the
thread length of the plug and to determine if any thread is exposed inside the
chamber. This must be done with the cylinder head removed from the engine. If any
thread is exposed to the chamber the temperature of the strap electrode will be raised
significantly. The strap electrode looses heat to the cylinder head via the transmission
path of the threads.
The threads that are engaged within the head can still get dark deposits on them. What
they indicate is the cylinder pressure. If the threads don’t show any signs at all of dark
creeping up the threads then the engine is a slug. A good engine will blow deposit
colouration up to 2 or even 3 threads.
Click to expand...
Yep. Bruce Robertson aka Shrinker. He also said this:

"Unleaded fuel makes exactly the same colorations as leaded. There is no difference in reading a plug on unleaded. If the plug wont color on unleaded its because you havent got good vaporization of the fuel. Unleaded is much harder to vaporize."
 
Here's @Mattax plugs and what Shrinker had to say:

Do they look familiar:

1713939158235.png


There is nothing happening in the cylinder. Theres no air being compressed. Its not even making enough bang to seal the rings, its even starting to look like its going to oil up the #3 plug soon. The general grey appearance is exhaust gas, its not even got enough blowdown to get rid of the exhaust.
You have a narrow LSA cam with not much duration that shuts the intake valve very early and you dont have enough compression ratio. So the cylinder isnt getting filled, and its not compressing what air its got in there enough. You not running on 1970's fuel anymore so bring the design up to the 21st century.

Cruise conditions with enough squeeze in a cylinder will give TAN sparkplugs on unleaded fuel. People say unleaded doesnt color plugs, BUNK -RUBBISH -BS. If you set a cruise mixture thats richer than stoich as a test and cant get a tan plug then your never going to burn a WOT mixture with maximum effect.
The manifold vacuum is a big part of getting a balance right between cruise and WOT. The narrow LSA destroys manifold vac. You need vacuum for cruise especially if you dont have compression. Stock motors have lots of vacuum and usually more compression pressure than what a lot of people get with hotrod engines. So thats why they run better.
Increasing the air flow of an engine is the way to get more power but it must be done without deterioration of the other factors.

Your plugs dont look like you have a distribution issue they look like you have a worn engine or one thats not equally built. Once you drop into this range of combustion issues your wide open to small variances, all of a sudden those small variances create glaringly obvious burn differences. It can be variances with any component of the whole system. Very difficult to find and fix.

Greg from @carby tuning techniques had this to say:

Hi Mattax,
That engine doesnt have any heat energy.It just doesnt have any grunt.
Those plugs show that its not squeezing the fuel and its not vaporising it very good either.
You need to get rid of that manifold,and put a single plane on there and raise the compression so that you can convert the liquid fuel to a gas.
Its a typical undercompressed cylinder that the plugs show.When you cant get brown colour on the plugs the engine just cant convert enough of the HC.
Its not so much your carb, its more the engine under it that is not up to speed.
 
Hysteric said:
Here's @Mattax plugs and what Shrinker had to say:

Do they look familiar:

View attachment 1716240894

There is nothing happening in the cylinder. Theres no air being compressed. Its not even making enough bang to seal the rings, its even starting to look like its going to oil up the #3 plug soon. The general grey appearance is exhaust gas, its not even got enough blowdown to get rid of the exhaust.
You have a narrow LSA cam with not much duration that shuts the intake valve very early and you dont have enough compression ratio. So the cylinder isnt getting filled, and its not compressing what air its got in there enough. You not running on 1970's fuel anymore so bring the design up to the 21st century.

Cruise conditions with enough squeeze in a cylinder will give TAN sparkplugs on unleaded fuel. People say unleaded doesnt color plugs, BUNK -RUBBISH -BS. If you set a cruise mixture thats richer than stoich as a test and cant get a tan plug then your never going to burn a WOT mixture with maximum effect.
The manifold vacuum is a big part of getting a balance right between cruise and WOT. The narrow LSA destroys manifold vac. You need vacuum for cruise especially if you dont have compression. Stock motors have lots of vacuum and usually more compression pressure than what a lot of people get with hotrod engines. So thats why they run better.
Increasing the air flow of an engine is the way to get more power but it must be done without deterioration of the other factors.

Your plugs dont look like you have a distribution issue they look like you have a worn engine or one thats not equally built. Once you drop into this range of combustion issues your wide open to small variances, all of a sudden those small variances create glaringly obvious burn differences. It can be variances with any component of the whole system. Very difficult to find and fix.

Greg from @carby tuning techniques had this to say:

Hi Mattax,
That engine doesnt have any heat energy.It just doesnt have any grunt.
Those plugs show that its not squeezing the fuel and its not vaporising it very good either.
You need to get rid of that manifold,and put a single plane on there and raise the compression so that you can convert the liquid fuel to a gas.
Its a typical undercompressed cylinder that the plugs show.When you cant get brown colour on the plugs the engine just cant convert enough of the HC.
Its not so much your carb, its more the engine under it that is not up to speed.
Click to expand...

That’s some bullshit right there.

I’ve been pulling fuel from a BBC for 18 pulls. The plugs started out black and now they are nice and clean and white with a pretty dry shell.

And guess what??? It’s making more power.
 
Here are two plugs from an engine I’m tuning.

The plug with the shell on is where I started. Way fat.

The plug with the shell off is the last pull yesterday. It’s close but not there yet.

There is probably 8-10 hp left with carb changes but it’s still a bit fat. I could put fuel back in it, but it will lose power.


IMG_0951.jpeg
IMG_0952.jpeg
 
Newbomb Turk said:
Here are two plugs from an engine I’m tuning.

The plug with the shell on is where I started. Way fat.

The plug with the shell off is the last pull yesterday. It’s close but not there yet.

There is probably 8-10 hp left with carb changes but it’s still a bit fat. I could put fuel back in it, but it will lose power.


View attachment 1716241037View attachment 1716241038
Click to expand...
The new plug looks rich towards the top end of RPM. Getting better... Can't see the ground strap to see where timing is at in these pics
 
Newbomb Turk said:
I’ve been pulling fuel from a BBC for 18 pulls.
The plugs started out black and now they are nice and clean and white with a pretty dry shell.

And guess what??? It’s making more power.
Click to expand...
You've done 18 pulls and now all of a sudden you're an expert?

Image how much more power it will make when you you get the cylinder pressure up high enough to tan the plugs......
 
Hysteric said:
You've done 18 pulls and now all of a sudden you're an expert?

Image how much more power it will make when you you get the cylinder pressure up high enough to tan the plugs......
Click to expand...

18 pulls on this engine slick. You haven’t explained why more color on the plug is losing power.

It can’t be the carbs are too big because they would be small on a 380 inch engine.

It can’t be the fuel isn’t atomized well because I’ve seen that and this ain’t it.

There you have it. You don’t have a clue what you are talking about. And you talk a lot.
 
Newbomb Turk said:
18 pulls on this engine slick. You haven’t explained why more color on the plug is losing power.
Click to expand...
What's the 5 gas telling you the gas balance is and what's the calculated AFR?
What's the arc duration time and how smooth is it?
What are you using to log the data from the pull?
 
Hysteric said:
What's the 5 gas telling you the gas balance is and what's the calculated AFR?
What's the arc duration time and how smooth is it?
What are you using to log the data from the pull?
Click to expand...

Don’t have a 5 gas. Looked into it. It’s a fools errand unless you think you need to save the world.

I haven’t hooked up the scope to it yet. Probably won’t. It’s a 630ish hp engine. A decent Chrysler ignition would fire it.

I use Performance Trends to run the dyno.

Let me see if I follow your logic here…

You think the area around the plug is lean. So lean it won’t color the plug. But…taking fuel away from it is still gaining power.

If it was that lean at the plug and I made it leaner no ignition would fire the plug that lean.

And yet it picks up power as I go leaner. And it’s still rich.

Again, you are wrong. Someday you should look back on this and understand what a perfect dumb *** you are.

I’m on the phone with the best people in the country and they agree with me. And yet and still you continue to argue with no basis for it.
 
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