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MG MGB Technical - coil

Is the Lucas sports coil better than the standard one and therefore worth the extra money. If the sports coil gives a bigger and better spark, is that important for a 1968 mgb roadster used only for city and highway driving (i.e. no rallies or races). Would you recommend some other brand.

How much extra money are you being asked for?

I've got a non-name, from NAPA, coil installed at the moment and must admit it works fine, as far as I can tell.

Not as pretty, though.

Derek Nicholson

Jerry - the consensus on this board has been "no" a sports coil is not worth the extra $$$. I'm not exactly sure the reasoning - check the archives, there's lots of discussion on it.

I wish I had known prior to my shelling out for the brightly finished sport coil in my GT. It does look good, though.
John Z


as long as the engine is farly stock, any coil normal coil works O.K.

If the engine is capable to revs in acess of 6500 a sports coil might be better as it does not become that hot inside than a std. one.

I changed to the Lucas sport coil last year and did not find any difference to the old 'Ducellier' coil that was installed by a PO.


They tend to run very hot, I tried one and did not like it.
Stan Best

Jerry. A coil has a maximum potential voltage. About 20K volts for a standard coil and about 40K volts for a Sports Coil. When the points open, and the electric charge is induced into the secondary windings of the coil, the ones which power the high tension (HT) circuit, the voltage in the coil continues to build until the the system grounds itself. (This, normally, happens by the built up electric current grounding itself by jumping the gap in the spark plug, this causeing a spark which ignites the mixture. Bad coil and/or spark plug wires or a dirty/wet spark plug can cause this discharge to take place to some other ground, causing a "misfire" of the spark plug.)

My engine analyzer is the old, large sized one rather than the modern style which can actually be carried inside the passanger compartment with the leads run through the firewall to the engine. This means that, without a chassis dynamometer (rolling road), I am limited to various forms of static tests.

My tests show that at an idle, or under a constant load, the required voltage to spark a set of plugs in good condition is 11K volts. There are some other tests which put more of a sudden load on the ignition such as snapping open the throttle for a second or two, then releasing it. This makes a change in the fuel/air charge entering the cylinders and raises the required voltage build up to about 14K volts. The only way, with my set up, I have been able to require the coil to produce its maximum potential voltage is by removing a spark plug lead and holding it away from the spark plug terminal until it sparked to the terminal. The distance involved was about one half inch from the spark plug terminal when the coil produced 20K volts (standard coil) or about 3/4" from the terminal when the coil produced 40K volts (Sports Coil).

I then cross checked my experiments with an experienced professional mechanic and he agreed that the results I had obtained were the same that he has obtained on cars of similar vintage with similar ignition systems. (He has been in the business for 20 years, owns his own, well equipped shop and he and his mechanics spend several evenings per month in recurring training, upgraded skills training which his shop pays for. In other words, someone I believe I can trust as a professional and a source to verify my experiments.)

Thus, my conclusion is the standard coil is sufficient for day to day operations for the majority of users. The potential of the Sports Coil is wasted in normal driving because it never reaches its potential. The condition of the entire ignition system is fully as important as the coil and will deteriorate more rapidly. Thus, good quality wires, rotor, and distributor cap, along with good spark plugs, will make more of a difference than the coil used.

As an aside, I believe that, when a problem is beginning to develope, the use of a Sports Coil will cause the deterioration of the system to accelerate more quickly than it would if a standard coil was in use. When a grounding situation begins to happen in the rotor (as is known to happen with some of the Lucas rotors provided in the last five years) or when a spark plug wire begins to leak through its insulation, there may be a higher voltage build up in the Sports Coil than would be possible in a standard coil and the higher voltage can cause the system to fail more quickly. Unfortunately, I have not figured out how to test this hypothesis yet.

Bottom line. The Sports Coil looks very nice and I use them because they came in the various "ignition kits" I have purchased over the years. I do not, however, consider them necessary to the proper functioning of the ignition system.

Les Bengtson

I thank all of you for your timely, considered replies. I will get an ordinary coil as there seems to be unanimity that it is sufficient.

I would like to describe a problem and ask for further advice. My 1968 MGB began suddenly stalling several weeks ago, particularly when idling at traffic lights. No warning, no sputtering; just died. However, I could turn off the ignition and turn it back on and the red beauty would start right up and sound fine. No cylinders missing, nothing obvious. It just stalled out constantly.

I thought it might be the coil or condenser or some other electrical part. I looked at my coil (I had the sport version), noticed that the wire from the central tower was wet, took coil off, saw the tower was damp, believed that oil was leaking out, threw it away.

Put in an old Bosch coil I haven't used in 10 years or more. Engine cranked but didn't catch. With ignition off, removed tower wire from the distributor end, hooked up another wire to crank the engine but got no spark when I held the distributor end of the wire near the engine block. Therefore, I believe I that the Bosch coil is also no good. I ask because I'm wondering if I should be doing this with the ignition turned on.

Pardon the length. Thank you.


Yes, You should turn on the ignition switch, power for the coil isn't available unless the switch is on.

Clifton Gordon

A higher voltage system like a Sport coil *might just* make the difference between starting and not starting under adverse conditions like poor state of tune, cold wet weather where the engine is saturated in condensation. etc., but only if the spark plug gaps have been opened up to allow a higher HT build-up. Other than they make very little difference except getting hotter than a standard coil. You can achieve the same effect (getting it started in adverse conditions) with a standard coil by pulling the coil HT lead out a little way while you crank.
Paul Hunt 2

Note that original coils on non-ballast MG were "semi-sports", designated HA12, with about 30-34k max output. Ordinary coils on Morris, Austin, etc,. were LA12, at 20k, and Sports coils were SA12 at 40k. You gain nothing by replacing an HA with SA, so long as the engine is not near full race spec and use.
FR Millmore

Les, your test of holding the spark plug lead a distance away from the plug to test a long gap versus voltage does not directly relate to the spark gap in an engine.

The distance a spark can jump the gap is strongly influenced by the air pressure and composition of the gasses that it must cross. At the higher pressures inside a combustion chamber it takes a much higher voltage than in low ambient pressure outside air. Add to that the fuel charge and it increases further.

Now in a high performance engine that has a higher compression ratio the voltage requirements will be even greater. If there is additional scavenging effect that will raise the fuel/air charge density further, again upping the voltage requirement. Worst case would be an engine with a supercharger or turbocharger producing maximum horsepower. These are the scenarios that the high voltage sports coil was intended to address. Basically it can provide a benefit in a high performance engine under racing type conditions.
Gerald O'

This thread was discussed between 30/08/2006 and 01/09/2006

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