Spark Plug Indexing

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Page created by T Mar 22nd 2008, compiled from info provided by Rosco1. Tables kindly supplied by Deb (Mrs condoHK69):

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Blue 3.3 6 Cyl CF Bedford Engine. Inappropriate positioning of the Ground Electrode.  Photo by reppilF. Click to Enlargen.

Spark Plug Indexing:

Essentially, this refers to the positioning of the Ground Electrodes of each Spark Plug for optimum efficiency. 

An example of Indexing likely to remove shadowing from the Centre electrode. The links show alternative schools of thought. Image by T. Click to Enlargen.
Blue 3.3 6 Cyl CF Bedford Engine. The larger Valve is the Inlet Valve.  The Open Gap of the Plug should be rotated from this position so that the gap is directly exposed to both the Piston Crown and the Exhaust Valve.  Photo by reppilF. Click to Enlargen.
  **The Ground Electrode should be positioned so that the open gap is exposed to the piston crown and exhaust valve side of the combustion chamber.(Holden V8 engines)Other engines will require different positioning of the plugs as different designs(head, intake, exhaust) play a part in dictating actual swirl direction inside any given combustion chamber. 
Blue 3300 6 Cyl CF Bedford LPG Engine. Note the better positioned Plugs don't show ash. The closest cylinder has an appropriately positioned Spark Plug. Photo by reppilF. Click to Enlargen.
VB 6 Cyl Head. Note the Flame Trail that has been passing from the Inlet Valve (larger) and across the Plug because the Plug has been Indexed correctly. Photo by Stef666. Click to Enlargen.
 To verify the correct position in which to point the plugs in your particular engine, follow the method used at the beginning of the below listed tests(test 1), meaning, reset your plugs so that they all face 1 way(North) and then allow the plugs to "soil" for a few days. This will enable you to "read" each individual "J" strap upon removal, and positively determine which side of the strap displays evidence of spark activity. This evidence will appear as a small shiny spot on the side of the strap, and will be devoid of carbon deposits, whereas the rest of the "J" strap will have a light carbon coating. You want to face the open area of the spark plug in the same direction as that which showed evidence of spark activity. The very reason this evidence is apparent at all is due to the swirl direction of the incoming fuel/air mixture, blowing the spark plasma out from between the spark plug electrode and earth strap("J"). By pointing the open gap in either the East or West position, relative to the configuration of the valvetrain on each cylinder, you will allow for the best propagation of the flame front generated by the sparking event. The direction that the flame front will head is directly related to the swirl direction of the air/fuel vapour that's entering the cylinder. The obvious advantages to doing it this way can be seen when looking at the test results posted below. Note the temperature changes and other relative information in all the tables below, this is clear proof that "indexing" works. Spark plug indexing test results, concluding with the installation of the Brisk concept spark plugs.*V8 Engine. Test 1 saw all the spark plugs indexed to the North point, meaning that the open end of the plug was facing the roof of the combustion chamber in all cylinders. 
Image by Rosco1. Click to Enlargen.
Image by Rosco1. Click to Enlargen.
When looking at the compass rose depicted here, North is always up, and the E & W are relative to the directions required when looking at the cylinder bank side on. The car was idled until it was up to normal operating temperature prior to the conducting of the tests. I allowed the thermo fans to activate 3 times before any readings were taken. Each test saw the same procedure applied. Engine idle was fluctuating between 920 and 970 RPM throughout the test. It was noted that the engine started easily. CO% was 10.00% at it's peak reading. **Exhaust temperature measurements were taken with a laser thermometer, aimed at a point approximately 2 inches back from where the pipe is welded to the header plate. **Spark plug shell temps were taken by firing the laser at the metal area of each spark plug, where the metal meets the ceramic insulator. **Cylinder head temps were taken approximately 1 inches from each spark plug hole.(please note that there are likely bad readings here as I had no way of determining where the water jackets were. (relevant to the firing order)
                     Exhaust temps.                    Plug shell temps.          Cyl head temps.
Cyl no 1,      470 (degrees C)    220                     189
Cyl no 2,      480                     212                     258
Cyl no 3,      600                     290                     283
Cyl no 4,      610                     315                     257
Cyl no 5,      540                     505                     355
Cyl no 6,      620                     530                     570
Cyl no 7,      460                     515                     240
Cyl no 8,      520                     425                     260
 On shut down, the engine "ran on" for 1-2 seconds.It was noted that no water was present in the exhaust output.The spark plugs were then removed and examined closely.It was noted that each plug showed clear evidence of spark activity in the form of a shiny or clear spot on the earth strap where the spark was jumping off. I had intentionally set the carby so that the engine ran rich, that way it enabled a soot to build up on each plug, highlighting the spark activity points more clearly. Pay careful attention to this next bit of information as it's important. The spark activity appeared on a particular side of each earth strap, this is relative to the geometry of the valvetrain and is directly related to the swirl direction of the incoming fuel/air mass, so care needs to be taken when interpreting this information and understanding what it all means. ** Remember each bank of cylinders has the intake valves layed out in a set fashion, mirrored on the opposite bank. The front 4 cylinders have the intake valves at the front, and the rear 4 cylinders have the intake valves at the rear. The information below indicates which side of the earth strap showed evidence of spark activity. This is important information, as it tells you which way the swirl effect is going. You can figure this out in other ways, but for the sake of this testing procedure, I felt that it should be shown in this fashion. 
Image by Rosco1. Click to Enlargen.
Image by Rosco1. Click to Enlargen.
Image by Rosco1. Click to Enlargen.
Image by Rosco1. Click to Enlargen.
(relevant to the firing order)Cyl no 1, W side of the earth strap showed evidence of spark activity.Cyl no 2, ECyl no 3, WCyl no 4, ECyl no 5, ECyl no 6, WCyl no 7, ECyl no 8, W Test 2. Using the above evidence of spark activity information as my guide, I then re indexed the plugs so that the open area of each plug was facing into the swirl of fuel/air mass, and it would also mean that the spark was being blown back into the "J" gap of the strap. This is the worst way to set a plug array. I intentionally did this, in order to give you a worst case scenario, as well as have a baseline from which to compare the later tests.  Do not index your plugs this way. 
Image by Rosco1. Click to Enlargen.
Image by Rosco1. Click to Enlargen.
Image by Rosco1. Click to Enlargen.
Image by Rosco1. Click to Enlargen.
(relevant to the firing order)Cyl no 1, E was the direction I pointed the open area of the plug toward.Cyl no 2, WCyl no 3, ECyl no 4, WCyl no 5, WCyl no 6, ECyl no 7, WCyl no 8, E On start up, the engine would not fire and needed to have throttle applied. This caused a major backfire. Once running, the engine was noticeably shuddering and the odour of unburnt fuel was highly noticeable anywhere near the vehicle. When stepping up the engine revs, the shudders remained.Engine idle was fluctuating between 660 and 720 RPM. CO% was 8.36% at it's peak. A substantial amount of water was evident in exhaust output. This remained constant throughout the test. (relevant to the firing order)
                  Exhaust temps.                  Plug shell temps.                        Cyl head temps.
Cyl no 1,      440 (degrees C)         220                           220
Cyl no 2,      510                         200                            215
Cyl no 3,      520                         280                            276
Cyl no 4,      635                         300                            330
Cyl no 5,      680                         500                            325
Cyl no 6,      530                         500                            310
Cyl no 7,      565                         470                            485
Cyl no 8,      540                         430                            260
 On shut down, the engine "ran on" for 6-7 seconds. Test 3. Using the above information, I re indexed the plugs so that they faced the exact opposite way, so now the open area of each plug was facing in the same direction as the swirl of fuel/air. This will allow the swirling fuel/air mass to drag the spark away from between the earth strap and the electrode, and the resulting flame kernel will not be hindered by any of the relative plug components. ***This would be the optimum way to index the plugs. (relevant to the firing order)Cyl no 1, W was the direction that I pointed the open area of the plug.Cyl no 2, ECyl no 3, WCyl no 4, ECyl no 5, ECyl no 6, WCyl no 7, ECyl no 8, W Engine idle was fluctuating between 850 and 920 RPM throughout the test. It was noted that the engine started instantly and ran smoothly, with only minimal evidence of shuddering. CO% was 9.75% at it's peak reading. Distinctly cleaner exhaust output was noted, with only a small amount of water evident. Unburnt fuel odour was markedly decreased.  (relevant to the firing order)
          Exhaust temps.               Plug shell temps.                    Cyl head temps.
Cyl no 1,      250 (degrees C)       130                   150
Cyl no 2,      275                        119                   115
Cyl no 3,      310                        149                   146
Cyl no 4,      365                        152                   150
Cyl no 5,      330                        197                   164
Cyl no 6,      279                        278                   299
Cyl no 7,      315                        143                   270
Cyl no 8,      260                        216                   241
 On shut down, the engine "ran on" for 1-2 seconds. This concluded the indexing test. Test 4Installed the Brisk concept spark plugs.No indexing required. Engine idle was fluctuating between 950 and 990 RPM throughout the test. It was noted that the engine started instantly and ran very smoothly. CO% was 8.14% at it's peak reading. Distinctly clean exhaust output was noted, with only very small amount of water evident. Unburnt fuel odour was again low. (relevant to the firing order)
        Exhaust temps.                 Plug shell temps.                       Cyl head temps.
Cyl no 1,      227 (degrees C)      104                    74
Cyl no 2,      269                       115                    88
Cyl no 3,      308                       144                    137
Cyl no 4,      347                       122                    175
Cyl no 5,      297                       287                    162
Cyl no 6,      296                       176                    159
Cyl no 7,      321                       255                    276
Cyl no 8,      282                       149                    138
 On shut down, the engine "ran on" for 1-2 seconds. The car was put away at this time, it was noted however, that the wheels easily broke traction with minimal effort, and this was with only minimum throttle being applied. This concludes the test shedule. I can now go ahead and adjust the Idle and timing of the engine and reset the carby to suit the Brisk spark plugs. As you can clearly see by the information above, it is certainly worthwhile indexing your "J" gap spark plugs, and for those willing to pay the price for the Brisks, you can clearly see the advantages of running these types of spark plugs. I hope this information proves helpful. 

How to Index:

Indexing Washers can be purchased which cause the Spark Plug to tighten to the preferred location. Alternately buying 2 sets of plugs and trying each until the Ground Electrode is favourably positioned is another. 

Indexing Information From Rosco1:

rosco1 on Sat, 08/03/2008 - 20:57.
I first heard about indexing when I was about 20 years old, I've used it religiously ever since, on any and all engines.Upon hearing about it, and giving it some careful thought, it was immediately apparent to me that there was something to it. I am all ears with regard to "insider tricks", as we all know, performance tuning "tricks" can go a long way.  The fellow I heard it from was definitely "in the know", he was right into rally tuning and was very knowledgeable, so attention to his methods was always beneficial. The idea of gaining just that "little bit more" over the next competitor, while keeping within the rules has been going on forever in all forms of motorsport. Many good competition drivers and tuners know about "indexing" too, I've heard of blokes in HQ racing who swear by it. Apparently the time that can be gained per lap justifies it. As you know, a small gain per lap, added to by each further lap, means you can sneak away and make quite a bit of distance on another competitor. Imagine how a gain of say 2 or 3 seconds per lap will look at the end of a Bathurst 1000 race, food for thought I reckon. The principal is sound and the benefits are very hard to ignore. If you index your old plugs, you will certainly "notice" a difference. You will also see an improvement by doing this with HEI ignitions, indeed any ignition system will give you that "little bit more", if plug indexing is adopted. If you can get your head around the principal, you will never do it any other way. That said, it's not just as simple as chucking in a set of indexed plugs, it goes further.I'm a firm believer in "reading' plugs too, and tuning by plug colour. Most people think that there's only black or white(rich or lean) with regard to plug colour. Most have never looked into it further. Once you're running indexed plugs, you can then take it that one step further, and tune the carby using the plug colour as your guide. Pull a spark plug out of a fuel injected car, what colour is the insulator around the electrode? In the old days, it was redish/honey brown in colour. These days the different fuel mobs use different dyes in their fuels, so they can be identified at a glance for what they are. A plug on a fuel injected engine will display the colour of the dye in the fuel, if you can tune your carby engine to match that, then you're 100 miles in front of the next bloke. You will get better fuel economy, due to having more power, think about it. Pretty much every fuel has a different coloured dye in it these days. If you religiously fuel your car at the same place, with the same fuel, you can tune it by "colour". You want to make small changes to the carb, not 1/4 turns or 1/2 turns. If it's lean, richen it by 1/10th of a turn, drive it, then pull a plug, read that, if it's still lean, go another 1/10th of a turn. You will eventually get it to the point where you will see the insulator around the electrode displaying the colour of the dye in the fuel. You can't get it any better than that on a carburettered engine! You would have heard fairytales about a tailpipe running grey, so thereby the engine is running right, well if it's running grey at the tailpipe, how lean must it be in the actual combustion chamber? Pull a plug and you will find it's white(lean). Completely disregard "tailpipe" colours, I know it's hard to do, as I had to get past that myself, but when careful thought is given to all this, you can see which way is right and which way is wrong. Anyway, today we are using Unleaded, so tailpipe colours are now a thing of the past. I actually saw a documentary on ABC years ago, and somehow, they were able to video the workings of a combustion chamber using some sort of thermal imaging, you could "see" the incoming fuel/air mix, you could "see" it swirling, then compressing, then combusting, the whole thing. That was amazing to me, and showed to me the benefits of "pointing" the open end of a spark plug in such a way, as to get the most out of the sparking event. Remember, the swirl of the fuel/air draws the spark out from between the electrode and the earth strap, so it effectively lengthens the spark as well. Instead of being straight, like this "I", it forces it into a "C <" shape, so as you can see, it's physically longer, and given that it's protruding out and away from the electrode and earth strap, it has more chance to ignite the fuel/air that's passing by it. Do it, you won't regret it. Keep the dark details to yourself too, and have a sly giggle at everyone else who "think" they know what they're on about. Regards,
Ross.My Shed
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Indexing Thread

ReppilF's Shed

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