MSD Spark Plug Recommendation
02-09-2002, 07:59 PM
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MSD Spark Plug Recommendation
Well, I'm just finishing up my MSD and Blaster 2 coil installation and was wondering what plugs and gap other MSD installers are using. The manual says to start at 0.050, I had Bosch Platinum 4s in there, but I don't think they would be right for the MSD, no way to adjust the gap. So before I fire it up I'd like some feedback, this is for my 89 944NA, thanks!
Mike
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02-10-2002, 05:25 AM
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I have the same engine, and same MSD setup... using BERU Silverstone now (silver core)
Was using Bosch Silver, but... I... uhh... dropped one. They seemed just as good.
I chose the Silver over the copper simply because of the greater conductivity... may be snake oil, who knows
Good Luck!
Was using Bosch Silver, but... I... uhh... dropped one. They seemed just as good.
I chose the Silver over the copper simply because of the greater conductivity... may be snake oil, who knows
Good Luck!
02-10-2002, 09:02 AM
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Thanks for the reply Skip, what plug gap do you run? Your previous install post was very helpful, it's tough to find a location for the MSD unit. I moved my vacuum canister to the intake side off the shock tower. The cruise and ABS lines were in the way.
Mike
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09-25-2004, 08:50 PM
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so is the gap-spec skip posted larger than OEM spec with the stock coil? I have the understanding that when I put my msd system in, i will have to gap more than usual to get full potential out of the msd...?
09-25-2004, 10:24 PM
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I’ve been running the MSD/Blaster combo for about 15 years now on various American and Foreign cars including my 924. MSD Techs will tell you to stay away from stock gaps because they will stress the MSD unit. I killed one unit in about 2 years of driving with a stock gap (these units typically last 6 years for me). The idea is to get as large a gap as possible (biggest spark) without causing cross firing. Cross firing happens because of the old saying “the path of least resistance”. If the resistance at the plug gap is too high then the spark will jump to the next nearest ground with a lower resistance; like another ignition wire or directly from the wire to the engine block or distributor housing. This is where it gets tricky….
Resistance across a spark plug has several sources:
The spark plug gap, the cylinder pressure during sparking (the higher the pressure, the more resistance), how lean the mixture is (lean mixtures are harder to fire), outside humidity, wire resistance, etc. Cross firing can occur between cylinders because only the cylinder that is in compression stroke has high cylinder pressure while another cylinder may be in intake or exhaust stroke and has a lower gap resistance so the spark will jump across wires that are in close proximity to each other.
Cylinder pressure will be a function of atmospheric pressure in your area, air temperature, compression ratio/cam overlap, how advanced your ignition timing is, etc….
This is why MSD only gives you a starting gap (something like .02” over stock?) to work with that is pretty close to where you will probably end up. Unfortunately, it’s all trial and error. I’ve had good luck with .06” on most of my cars but usually have to dial up the fuel to get an easier mixture to fire. I haven’t been able to get much above .06” without cross firing on really rainy days due to wet wires (one reason low resistance wires are a must). IIRC the MSD tech told me to run the car at 3000 RPM for 2 minutes and immediately pull the plug and check for color, but I’ve never tried this method to give advise on it.
BTW, my 1978 924 (9.5:1) will not tolerate anything other than platinum plugs. For some reason anything else will only get about 7K before the tips erode away and in effect opened up my gap so the motor would cross fire constantly. The platinums have been on there for 100k without a problem.
Hope this helps!
Resistance across a spark plug has several sources:
The spark plug gap, the cylinder pressure during sparking (the higher the pressure, the more resistance), how lean the mixture is (lean mixtures are harder to fire), outside humidity, wire resistance, etc. Cross firing can occur between cylinders because only the cylinder that is in compression stroke has high cylinder pressure while another cylinder may be in intake or exhaust stroke and has a lower gap resistance so the spark will jump across wires that are in close proximity to each other.
Cylinder pressure will be a function of atmospheric pressure in your area, air temperature, compression ratio/cam overlap, how advanced your ignition timing is, etc….
This is why MSD only gives you a starting gap (something like .02” over stock?) to work with that is pretty close to where you will probably end up. Unfortunately, it’s all trial and error. I’ve had good luck with .06” on most of my cars but usually have to dial up the fuel to get an easier mixture to fire. I haven’t been able to get much above .06” without cross firing on really rainy days due to wet wires (one reason low resistance wires are a must). IIRC the MSD tech told me to run the car at 3000 RPM for 2 minutes and immediately pull the plug and check for color, but I’ve never tried this method to give advise on it.
BTW, my 1978 924 (9.5:1) will not tolerate anything other than platinum plugs. For some reason anything else will only get about 7K before the tips erode away and in effect opened up my gap so the motor would cross fire constantly. The platinums have been on there for 100k without a problem.
Hope this helps!
Last edited by 82-928/89-S2; 09-25-2004 at 11:04 PM.
09-26-2004, 12:57 AM
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thanks nick! my 944 is running 10.9:1, and I will be putting in single-electrode bosch platinum plugs, so I'll try a gap no higher than .06" and see what I get...
your explanation of cross firing was very vivid, but how will I know if my engine is doing so?
your explanation of cross firing was very vivid, but how will I know if my engine is doing so?
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09-26-2004, 06:13 AM
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Don't have to worry about it too much on the 944 since you're going through the distributor. So only one spark-plug is connected at any one time, no wasted-spark configuration. I've been trying to quantify this upgrade for a while now and haven't a chance to do it personally. If you want to dyno-test the car with stock ignition and then with the MSD/blaster combo, I'll gladly pay for your dyno charges.
09-26-2004, 01:59 PM
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Hi Ian,
Thanks for the compliment. You have a good question and I’m sorry I didn’t put this info in previously cuz you will need it. There’s really only 2 ways that I’ve used to monitor cross firing. The number one way I use is to pay close attention during start-up. A motor that’s cross firing will kick and buck with an occasional backfire due to the fact that the wrong spark plugs are being fired. Once the car starts, you will feel it run rough (like you had too much timing advance). The car should start up smooth and effortlessly and run smooth. The second is to watch for the dreaded “blue aura” which I will discuss in a minute (The MSD techs flagged me on this).
There are 2 ways that I know of that cross firing can occur. The first is the one I’ve read about the most which involves parallel run wires that are very close together. As current travels through one wire, the magnetic field it produces will actually “induce” a current in the one next to it. Wire looms serve as a way to keep wires separated to help avoid this and you are recommended to actually cross the wires 90 degrees at some point during the wire run to avoid this magnetic coupling. The second is the way I wrote about earlier where you have a huge resistance somewhere in the ignition system. The spark energy can reach levels where the dielectric strength/travel path of the insulating materials in the wires, cap, rotor, coil, etc. can no longer resist energy traveling over them. When this happens you can actually see a pronounced blue aura that’s produced (in humid weather) if you look at a running engine in pitch-blackness…it’s really amazing. This is the second way I test to see if my spark plug gaps are too high.
You can actually see a fuzzy blue trail of spark energy crawling down the coil tower to the positive and negative electrodes on the coil. The aura should be plainly visible in humid weather and will get more pronounced depending on how bad your situation is. (I’ve noticed there is usually a very tiny amount of aura regardless of spark plug gaps but you really have to strain to see it). The real high-energy coils have very tall towers with accordion style necks to try to increase travel path that the energy would have to overcome (Bigger diameter wires also help to decrease spark energy losses). You will see the aura on the wires where they come in contact with other wires or ground surfaces and can actually see paths of blue energy bridge through the air as you move the wires closer to each other! The caps have more of a tendency to produce carbon trails internally with higher power ignitions and this could be a source of cross firing over longer periods of time,.. Something to watch for.
Humid weather where the car has sat for a couple of days can allow air inside the cap to breath in moist air as the ambient air outside heats up and cools again. This can cause cross firing as condensation will enhance the ability for a spark to travel over surfaces (also true with the wires, coil, outside of cap and spark plugs). It’s in damp weather that you actually want to test your spark plug gaps by watching for this blue aura. Mechanics will take a Windex bottle filled with water and spray a fine mist directly on the wires in pitch-blackness with the engine running to check for bad wires (wires that have had there internal resistances go up) on a car.
The cap on my 924 has always aggravated cross firing because of its puny diameter and it likes to carbon trail on me quite a bit so it gets changed often.
Ian, you mentioned you were going to go for the .06” right away. I would recommend playing it conservative and starting out with a small increase over stock and work your way up from there. Cross firing is NOT good for the motor. I handle spark plug gaping the same way I do with advancing the timing…start off low and work my way up while driving it for a couple of days to get a feel for it’s behavior.
Good Luck!
Thanks for the compliment. You have a good question and I’m sorry I didn’t put this info in previously cuz you will need it. There’s really only 2 ways that I’ve used to monitor cross firing. The number one way I use is to pay close attention during start-up. A motor that’s cross firing will kick and buck with an occasional backfire due to the fact that the wrong spark plugs are being fired. Once the car starts, you will feel it run rough (like you had too much timing advance). The car should start up smooth and effortlessly and run smooth. The second is to watch for the dreaded “blue aura” which I will discuss in a minute (The MSD techs flagged me on this).
There are 2 ways that I know of that cross firing can occur. The first is the one I’ve read about the most which involves parallel run wires that are very close together. As current travels through one wire, the magnetic field it produces will actually “induce” a current in the one next to it. Wire looms serve as a way to keep wires separated to help avoid this and you are recommended to actually cross the wires 90 degrees at some point during the wire run to avoid this magnetic coupling. The second is the way I wrote about earlier where you have a huge resistance somewhere in the ignition system. The spark energy can reach levels where the dielectric strength/travel path of the insulating materials in the wires, cap, rotor, coil, etc. can no longer resist energy traveling over them. When this happens you can actually see a pronounced blue aura that’s produced (in humid weather) if you look at a running engine in pitch-blackness…it’s really amazing. This is the second way I test to see if my spark plug gaps are too high.
You can actually see a fuzzy blue trail of spark energy crawling down the coil tower to the positive and negative electrodes on the coil. The aura should be plainly visible in humid weather and will get more pronounced depending on how bad your situation is. (I’ve noticed there is usually a very tiny amount of aura regardless of spark plug gaps but you really have to strain to see it). The real high-energy coils have very tall towers with accordion style necks to try to increase travel path that the energy would have to overcome (Bigger diameter wires also help to decrease spark energy losses). You will see the aura on the wires where they come in contact with other wires or ground surfaces and can actually see paths of blue energy bridge through the air as you move the wires closer to each other! The caps have more of a tendency to produce carbon trails internally with higher power ignitions and this could be a source of cross firing over longer periods of time,.. Something to watch for.
Humid weather where the car has sat for a couple of days can allow air inside the cap to breath in moist air as the ambient air outside heats up and cools again. This can cause cross firing as condensation will enhance the ability for a spark to travel over surfaces (also true with the wires, coil, outside of cap and spark plugs). It’s in damp weather that you actually want to test your spark plug gaps by watching for this blue aura. Mechanics will take a Windex bottle filled with water and spray a fine mist directly on the wires in pitch-blackness with the engine running to check for bad wires (wires that have had there internal resistances go up) on a car.
The cap on my 924 has always aggravated cross firing because of its puny diameter and it likes to carbon trail on me quite a bit so it gets changed often.
Ian, you mentioned you were going to go for the .06” right away. I would recommend playing it conservative and starting out with a small increase over stock and work your way up from there. Cross firing is NOT good for the motor. I handle spark plug gaping the same way I do with advancing the timing…start off low and work my way up while driving it for a couple of days to get a feel for it’s behavior.
Good Luck!
Last edited by 82-928/89-S2; 09-26-2004 at 10:09 PM.
09-27-2004, 04:30 AM
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Let's take a look at the MSD durability issue in another way. There are two coils windings. The primary is about 0.5-1.0 ohms typically with the high-voltage secondary being in the 15K+ range. Which one has a more direct affect on the driver circuits in the MSD box?
" A motor that’s cross firing will kick and buck with an occasional backfire due to the fact that the wrong spark plugs are being fired. Once the car starts, you will feel it run rough (like you had too much timing advance)."
This sounds more like leaky plug wires. If you're getting arcing that's visible at night, what's the path of least resistance? The block or another insulated plug-wire? For a high-voltage charge to prefer to jump through another insulator, then go through a second plug-gap, it has to overcome quite a lot more resistance than going directly to the block. I think faulty or bad plug-wires are the culprit here. The spark energy that should be though through the plug is leaking though craks in the wires and gets drained by the block (the plug's not firing). If we do a search here for "plug wires arcing", we'll see that simply replacing the plug wires solves these rough start-up issues.
Another thing about electrical circuits is that you cannot force current to flow. It will only flow the path of least resistance and only in the amount afforded by that resistance; V=IR or I=R/V. So the higher the resistance, the less the current flow. At some point with increasing resistance, the current just stops flowing altogether. Imagine if you had an infinitely large plug-gap. The activation energy of the mixture in between the electrodes would be infinite as well, thus the measly 45Kv outputed by the Blaster-2 coil won't be able to jump that gap. When the coil is dumped, the induced charge would have nowhere to go and will just dissipate through the ground end of the secondary.
As far as I know, Skip has the longest-running usage of the MSD/Blaster combo. Have you noticed any differences with various plug gaps?
" A motor that’s cross firing will kick and buck with an occasional backfire due to the fact that the wrong spark plugs are being fired. Once the car starts, you will feel it run rough (like you had too much timing advance)."
This sounds more like leaky plug wires. If you're getting arcing that's visible at night, what's the path of least resistance? The block or another insulated plug-wire? For a high-voltage charge to prefer to jump through another insulator, then go through a second plug-gap, it has to overcome quite a lot more resistance than going directly to the block. I think faulty or bad plug-wires are the culprit here. The spark energy that should be though through the plug is leaking though craks in the wires and gets drained by the block (the plug's not firing). If we do a search here for "plug wires arcing", we'll see that simply replacing the plug wires solves these rough start-up issues.
Another thing about electrical circuits is that you cannot force current to flow. It will only flow the path of least resistance and only in the amount afforded by that resistance; V=IR or I=R/V. So the higher the resistance, the less the current flow. At some point with increasing resistance, the current just stops flowing altogether. Imagine if you had an infinitely large plug-gap. The activation energy of the mixture in between the electrodes would be infinite as well, thus the measly 45Kv outputed by the Blaster-2 coil won't be able to jump that gap. When the coil is dumped, the induced charge would have nowhere to go and will just dissipate through the ground end of the secondary.
As far as I know, Skip has the longest-running usage of the MSD/Blaster combo. Have you noticed any differences with various plug gaps?
09-27-2004, 01:27 PM
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I am VERY interested in this upgrade for my car as well, anything you find out Danno let me know. I would do that upgrade now if you paid for my dyno time but just got a nice $2,200 bill this week on my car, so I don't plan on buying anything for it for awhile. Otherwise I would do it in a HEART beat!
09-27-2004, 01:34 PM
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verrry interesting stuff guys! All these daydreams in physics class last year are finally paying off...lol
Danno, I was originally considering doing a before and after dyno run, just to see... I just need to arrange a time and place to get it done way ahead of time, as my car is a daily driver... I'll let you know if I do.
Danno, I was originally considering doing a before and after dyno run, just to see... I just need to arrange a time and place to get it done way ahead of time, as my car is a daily driver... I'll let you know if I do.
09-27-2004, 03:16 PM
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Another thing to consider with the MSD unit is that it switches from multiple-spark to single-spark after a certain RPM, around 3000rpm I think. That's because of the time it takes to charge the coil, there's not enough time to do it more than once per cylinder. In which case, it operates similarly to the stock setup with a Blaster coil installed. On an NA car, I don't think that's an issue, but on Turbos where spark flame-out becomes an issue around 350rwhp, the hotter spark is definitely helpful over the stock set-up.
The MSD ignition gained a lot of popularity decades ago amongst the hot-rod muscle car crowd. With carbureted cars, it was difficult to adjust fuel across the board. So a lot of them had rich mixtures for full-throttle operation, but that resulted in to plug-fouling and poor partial-throttle drivability. The MSD with its multiple-spark was able to to keep the plugs clean and ensure complete combustion of a super-rich mixture. On our cars with efficient EFI, the benefits won't be as great, but I'd like to measure exactly what the gains are with quantifiable numbers.
Here's some discussion on which spark-plugs to use: What do you guys recommend for sparkplugs?
Ian, let me know what you find out about dyno times and rates.
The MSD ignition gained a lot of popularity decades ago amongst the hot-rod muscle car crowd. With carbureted cars, it was difficult to adjust fuel across the board. So a lot of them had rich mixtures for full-throttle operation, but that resulted in to plug-fouling and poor partial-throttle drivability. The MSD with its multiple-spark was able to to keep the plugs clean and ensure complete combustion of a super-rich mixture. On our cars with efficient EFI, the benefits won't be as great, but I'd like to measure exactly what the gains are with quantifiable numbers.
Here's some discussion on which spark-plugs to use: What do you guys recommend for sparkplugs?
Ian, let me know what you find out about dyno times and rates.
09-27-2004, 03:27 PM
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Good discussion. I've got a Jacobs Omni Magnum system, which is similar to the MSD, but luckiliy haven't seen any crossfiring probs (bought the thicker wires to match).
09-28-2004, 10:39 AM
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Hi Everyone,
I had a very enlightening phone conversation yesterday with one of MSD’s senior engineers that I would like to share with you before Alzheimer’s sets in.
I had never been completely satisfied with the reply I got from the MSD tech when I talked to him regarding my early MSD failure some years ago (discussed earlier), and a reply from Danno regarding longevity of the units was enough for me to want to get a second opinion and I’m glad I did.
This time I went right to the source so there would be no confusion….The Engineering Department. As it turns out Joe (Engineer) confirmed there is absolutely NO issue with running stock gaps on these MSD’s and in fact, as logic would have it, the units are actually less stressed with the smaller gaps….Thanks for keeping me honest Danno!
But while I had him on the phone I was able to get quite a bit of new information regarding these units and also clarify and correct some earlier posts due to some (as it turns out) bad information from MSD’s techs I had spoken with in the past.
As I stated earlier regarding cross-firing being an indicator of too extreme a plug gap, according to Joe, actual “misfires” are what most people are probably going to experience. By misfire I mean that the spark energy will find a convenient nearby ground to discharge on as opposed to cross-firing to other cylinders (Danno touched on this) as I have had ample experience with. This means my example of “bucking and kicking” at startup which applies to cross firing, will be more like a “miss” at idle or during driving/acceleration) so you should be on the look out for both. I have unfortunately had the bad luck of dealing with fairly small distributor caps on most of my cars and it seems this is where cross-firing becomes the predominant restriction for getting the maximum gap possible.
Another correction I want to make is that the “dreaded blue aura” I referred to earlier, while a tell tail indicator of trouble in a non-CD (Capacitance Discharge) ignition it is in fact characteristic of all CD ignitions which explains why I have always encountered it to some degree in these systems (on the entire system, not just the wires). Joe tells me that it’s actually referred to as a “blue corona” and is the generated magnetic field producing a visible light and does not necessarily indicate a problem, although if it’s extreme enough, it could be. Bottom line is Joe suggests that it NOT be used as an indicator for the general health of the ignition system which contradicts my earlier recommendation. I should mention that it was in fact an MSD tech that originally diagnosed a spark plug gap issue (correctly I might add) with my car way back when, as soon as I told him that I was seeing a “blue aura” on the wires and coil.
This brings me to answer a question that Danno had for me regarding some past experiences…
I wrote:
" A motor that’s cross firing will kick and buck with an occasional backfire due to the fact that the wrong spark plugs are being fired. Once the car starts, you will feel it run rough (like you had too much timing advance)."
Danno wrote:
“This sounds more like leaky plug wires. If you're getting arcing that's visible at night, what's the path of least resistance? The block or another insulated plug-wire? For a high-voltage charge to prefer to jump through another insulator, then go through a second plug-gap, it has to overcome quite a lot more resistance than going directly to the block. I think faulty or bad plug-wires are the culprit here. The spark energy that should be though through the plug is leaking though craks in the wires and gets drained by the block (the plug's not firing). If we do a search here for "plug wires arcing", we'll see that simply replacing the plug wires solves these rough start-up issues.”
My history with this problem went like this…
Installed an MSD-6A/Blaster coil in my 1978 924 with new spiral core wires and copper plugs. After 2 months of driving noticed engine slowly becoming more resistant to turning during cranking and then eventually bucking and back firing along with rough running once started. Happened to notice one night the “blue corona” on wires and coil (As Danno mentioned, normally an indicator of bad wires, but these were brand new ??). Removed wires off looms and suspended them away from each other and away from the engine/hood. Result: Car running great again. One month later same resistance to cranking slowly creeping in all over again with the eventual bucking and rough running just like before. I call MSD tech to see if he has any ideas. Once he hears about the “blue corona” he immediately says spark plug gaps too high. I pull plugs and all the sharp corners on the plug electrodes are rounded off and the gap has grown to over .07”…He was right. Put new plugs in and go again fine for another 2-3 months and go through the same cycle all over again. I did this routine for about 2 years and then got inspired to throw in a set of triple platinum split fires and have yet to touch them 4yrs/100k later. Car runs great (same wires).
This is where a lot of my experience is coming from with regards to cross firing. If I seemed to suggest earlier that non-magnetically induced cross firing often occurs directly between wires (through insulation), that was not my intention. As a matter of fact most of this form of crossfire that I’ve seen or read about (and Joe confirmed this) actually occurs inside the distributor cap due to high concentrations of ozone/ionized air produced during ignition and is aggravated by advances in timing since the rotor tip and cap tip are farther apart causing a longer spark to be produced inside the cap. The elevated voltages produced by the Blaster coil when larger spark plug gaps are used, amplifies the problem even more. This is why I’ve seen so many racers drill holes in the sides of their distributor caps in an attempt to improve ventilation of the ionized air out of them. I personally have not put this combo in a 944 yet, but looking at the difference in cap diameters compared to the 924, I wouldn’t expect to have anywhere near the cross firing issues I was seeing.
Now for some IMPORTANT information regarding wires for this set-up:
As long as I have been using this set-up, MSD has always had in their literature NOT to use solid core wires. Joe has STRONGLY reinforced this position with me and went into detail about 2 major problems with this construction. (I know that Skip has been using solid core wires for some time with this combo and I was trying to get a hold of him to see if any of what I’ve written below has reared it’s ugly head, but I was not been able to reach him for comment).
1) Even though OEM style solid core wires use internal resistors to control RF (in the Beru connectors), when these wires are used with the MSD/blaster combo there is a considerable level of RF produced which may not only affect the MSD unit, but also the DME or any other on board computers in the car.
2) Solid core wires have a much higher tendency to magnetically couple (induce voltage) in other wires running parallel to them as I described earlier, since their conductor runs straight (does not constantly change direction like a spiral core). This produces a condition known as “lean fire miss” which is for the most part a specific instance of “cross-firing”.
Joe explained that although solid core wires have typically lower resistance than spiral core, the magnetic emissions (noise) are much higher and as a result suffer from higher energy losses. Spiral core wires actually use their spiraling geometry to magnetically encapsulate all the energy into the wire. Joe also explained that you never want to use solid coil wires with any kind of grounded (conductive) protective sleeve as this will form a capacitor and act as a huge energy drain on the system.
Another interesting point is that the dielectric properties (resistance to electricity passing through an insulating material) of ignition wire insulation are always in the process of deterioration and will deteriorate faster with the higher voltages produced by larger spark plug gaps. He estimated wire replacement for your average daily driver using the high voltage set-up at somewhere close to once a year (seems high to me?).
I asked Joe if there was a point of diminishing returns with regards to maximizing the spark plug gap. He said yes, that after a certain point the gains become marginal but that it would have to be determined for each application.
…..Enter the Dyno… I’m really curious to see how that pans out….
FYI – Check out MSD’s 10 most asked questions…A lot of what I’ve discussed here is addressed including recommended gap sizes which are only .005”-.010” over stock to start with.
http://www.msdignition.com/pdf/tb_top_10.pdf
Hope this helps!
I had a very enlightening phone conversation yesterday with one of MSD’s senior engineers that I would like to share with you before Alzheimer’s sets in.
I had never been completely satisfied with the reply I got from the MSD tech when I talked to him regarding my early MSD failure some years ago (discussed earlier), and a reply from Danno regarding longevity of the units was enough for me to want to get a second opinion and I’m glad I did.
This time I went right to the source so there would be no confusion….The Engineering Department. As it turns out Joe (Engineer) confirmed there is absolutely NO issue with running stock gaps on these MSD’s and in fact, as logic would have it, the units are actually less stressed with the smaller gaps….Thanks for keeping me honest Danno!
But while I had him on the phone I was able to get quite a bit of new information regarding these units and also clarify and correct some earlier posts due to some (as it turns out) bad information from MSD’s techs I had spoken with in the past.
As I stated earlier regarding cross-firing being an indicator of too extreme a plug gap, according to Joe, actual “misfires” are what most people are probably going to experience. By misfire I mean that the spark energy will find a convenient nearby ground to discharge on as opposed to cross-firing to other cylinders (Danno touched on this) as I have had ample experience with. This means my example of “bucking and kicking” at startup which applies to cross firing, will be more like a “miss” at idle or during driving/acceleration) so you should be on the look out for both. I have unfortunately had the bad luck of dealing with fairly small distributor caps on most of my cars and it seems this is where cross-firing becomes the predominant restriction for getting the maximum gap possible.
Another correction I want to make is that the “dreaded blue aura” I referred to earlier, while a tell tail indicator of trouble in a non-CD (Capacitance Discharge) ignition it is in fact characteristic of all CD ignitions which explains why I have always encountered it to some degree in these systems (on the entire system, not just the wires). Joe tells me that it’s actually referred to as a “blue corona” and is the generated magnetic field producing a visible light and does not necessarily indicate a problem, although if it’s extreme enough, it could be. Bottom line is Joe suggests that it NOT be used as an indicator for the general health of the ignition system which contradicts my earlier recommendation. I should mention that it was in fact an MSD tech that originally diagnosed a spark plug gap issue (correctly I might add) with my car way back when, as soon as I told him that I was seeing a “blue aura” on the wires and coil.
This brings me to answer a question that Danno had for me regarding some past experiences…
I wrote:
" A motor that’s cross firing will kick and buck with an occasional backfire due to the fact that the wrong spark plugs are being fired. Once the car starts, you will feel it run rough (like you had too much timing advance)."
Danno wrote:
“This sounds more like leaky plug wires. If you're getting arcing that's visible at night, what's the path of least resistance? The block or another insulated plug-wire? For a high-voltage charge to prefer to jump through another insulator, then go through a second plug-gap, it has to overcome quite a lot more resistance than going directly to the block. I think faulty or bad plug-wires are the culprit here. The spark energy that should be though through the plug is leaking though craks in the wires and gets drained by the block (the plug's not firing). If we do a search here for "plug wires arcing", we'll see that simply replacing the plug wires solves these rough start-up issues.”
My history with this problem went like this…
Installed an MSD-6A/Blaster coil in my 1978 924 with new spiral core wires and copper plugs. After 2 months of driving noticed engine slowly becoming more resistant to turning during cranking and then eventually bucking and back firing along with rough running once started. Happened to notice one night the “blue corona” on wires and coil (As Danno mentioned, normally an indicator of bad wires, but these were brand new ??). Removed wires off looms and suspended them away from each other and away from the engine/hood. Result: Car running great again. One month later same resistance to cranking slowly creeping in all over again with the eventual bucking and rough running just like before. I call MSD tech to see if he has any ideas. Once he hears about the “blue corona” he immediately says spark plug gaps too high. I pull plugs and all the sharp corners on the plug electrodes are rounded off and the gap has grown to over .07”…He was right. Put new plugs in and go again fine for another 2-3 months and go through the same cycle all over again. I did this routine for about 2 years and then got inspired to throw in a set of triple platinum split fires and have yet to touch them 4yrs/100k later. Car runs great (same wires).
This is where a lot of my experience is coming from with regards to cross firing. If I seemed to suggest earlier that non-magnetically induced cross firing often occurs directly between wires (through insulation), that was not my intention. As a matter of fact most of this form of crossfire that I’ve seen or read about (and Joe confirmed this) actually occurs inside the distributor cap due to high concentrations of ozone/ionized air produced during ignition and is aggravated by advances in timing since the rotor tip and cap tip are farther apart causing a longer spark to be produced inside the cap. The elevated voltages produced by the Blaster coil when larger spark plug gaps are used, amplifies the problem even more. This is why I’ve seen so many racers drill holes in the sides of their distributor caps in an attempt to improve ventilation of the ionized air out of them. I personally have not put this combo in a 944 yet, but looking at the difference in cap diameters compared to the 924, I wouldn’t expect to have anywhere near the cross firing issues I was seeing.
Now for some IMPORTANT information regarding wires for this set-up:
As long as I have been using this set-up, MSD has always had in their literature NOT to use solid core wires. Joe has STRONGLY reinforced this position with me and went into detail about 2 major problems with this construction. (I know that Skip has been using solid core wires for some time with this combo and I was trying to get a hold of him to see if any of what I’ve written below has reared it’s ugly head, but I was not been able to reach him for comment).
1) Even though OEM style solid core wires use internal resistors to control RF (in the Beru connectors), when these wires are used with the MSD/blaster combo there is a considerable level of RF produced which may not only affect the MSD unit, but also the DME or any other on board computers in the car.
2) Solid core wires have a much higher tendency to magnetically couple (induce voltage) in other wires running parallel to them as I described earlier, since their conductor runs straight (does not constantly change direction like a spiral core). This produces a condition known as “lean fire miss” which is for the most part a specific instance of “cross-firing”.
Joe explained that although solid core wires have typically lower resistance than spiral core, the magnetic emissions (noise) are much higher and as a result suffer from higher energy losses. Spiral core wires actually use their spiraling geometry to magnetically encapsulate all the energy into the wire. Joe also explained that you never want to use solid coil wires with any kind of grounded (conductive) protective sleeve as this will form a capacitor and act as a huge energy drain on the system.
Another interesting point is that the dielectric properties (resistance to electricity passing through an insulating material) of ignition wire insulation are always in the process of deterioration and will deteriorate faster with the higher voltages produced by larger spark plug gaps. He estimated wire replacement for your average daily driver using the high voltage set-up at somewhere close to once a year (seems high to me?).
I asked Joe if there was a point of diminishing returns with regards to maximizing the spark plug gap. He said yes, that after a certain point the gains become marginal but that it would have to be determined for each application.
…..Enter the Dyno… I’m really curious to see how that pans out….
FYI – Check out MSD’s 10 most asked questions…A lot of what I’ve discussed here is addressed including recommended gap sizes which are only .005”-.010” over stock to start with.
http://www.msdignition.com/pdf/tb_top_10.pdf
Hope this helps!