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MG MGB Technical - Accel Super Coil

I have a 68 MGB that I put a Petronics unit in but used my old original coil, it works just fine but I have an Accel Super coil kicking around the garage and wondered if it would be O.K. to try, would there be any difference? Anyone run one of these? Thank you for any input.
BJW Brad Willey

Brad. Most of these "high performance" coils offer the potential to develope 40K volts rather than the 20K volts the normal coils offer. My experiments demonstarte that a good engine in good tune normally operates at less than 20K volts. Since the voltage in the coil only builds up sufficiently that the spark jumps the gap between the electrodes of the spark plug, but not more, having a "high performance" coil is not needed for most of us.

For the times when the required sparking voltages become greater than 20K volts and the 40K volt coil can actually produce more than 20K volts, the condition of the high tension circuit becomes critical. At the 11-15K volts it normally runs you might not see a problem. Run the voltage it has to carry up to 25-30K volts and any minor imperfections in the insulation of the wires, the connections, worn rotor, dirty spark plug bodies, etc. can cause the surge of electric current to ground to the engine outside rather than causing the spark plug to spark.

High performance coils look neat. They do not hurt anything. Most of the time they do nothing the standard coil would not be able to do. If you really need an upgraded coil, make sure the entire ignition system is well tuned and in excellent condition.

Les Bengtson

Depends on the current draw/resistance of the Accel coil, might be enough to melt your Petronics unit. Generally the secondary voltage will not rise above the ionization voltage of the system; spark plug gap and mixture/pressure and distributor cap/rotor gap. System voltage then drops dramatically to the voltage required to maintain the arc, usually 5 to 10 K. This arc voltage will last until the electrical energy in the tank circuit is depleted. Bigger coil, longer charge time (dwell) and bigger capacitor more energy in the system and the longer the arc/spark period. Will your engine run better (more HP or cleaner?) with more spark energy? I donít know, maybe chassis dyno a hand full of needles and an day of testing.
Leland Bradley

The Super Coil is rated as a 45,000 volt unit. pertronix highly recommendsd their own 40,000 volt "flame thrower" coil. I would suspect the Accel unit will work just as well as theirs. If all esle fails, Pertronix has a 30 month guarantee!
Jeff Schlemmer

I'm running the inexpensive version of the Crane electronic ignition with the Super coil with a ballast resistor and it works great. If you check the history threads I recall seeing prior posts about running "hot coils" with Pertronix with no problems.

Les's comments above are right on about hot coils. I had a bad plug wire and electricity starting jumping all over everywhere, except where it was supposed to be.

I'm running flat top hi compression pistons and .050" + spark plug gap and it all works great.

Barry Parkinson

What you get with the "HOT" coil is the ability to really open up the spark gap to 40 thou or more. This kind of gap gives you a real zap from the spark and a good light-off of the fuel/ air mix. I run my B at .045 gap with a Crane / Allison solid state Multi spark system to burn all the fuel that my 45DCOE Weber puts in there. Only problem is that when you do something really stupid and shock yourself, 40,000 volts really hurts. By the way, these new Kevlar reinforced radiator hoses now available WILL positively conduct electricity and give you the thrill of your life.
Wayne Hardy

Barry and Wayne,

Since both of you are using a fairly high spark plug gap can you please inform us to what other benifits this has.

I have the Flame Thrower 40K and Pert II with a gap of .038. Will opening up this gap,, plus with the supercharger be a plus or negative........

Ray 1977mgb

The engine seems to run smoother with the wider gap, however that is very subjective.

The wide gap really makes a difference in cold starting. I realize that is a non-existant problem where you live.

Try widening your gap. If your ignition system reaches it's limit, the engine will start misfiring under hi rpm load, or worse sparks will jump the shortest route to ground inside your distributor. If that happens you'll likely need a new cap and rotor.

Once those burn/carbon paths are etched it is hard to stop the spark from following those tracks as they are literally, the path of least resistance.

Barry Parkinson

Thank you all for the info. When I get a little time to mess with it I think I'll give it try.
BJW Brad Willey

This thread was discussed between 13/06/2006 and 15/06/2006

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