Coil advice

[Dom66]

I want to replace my coil. I have a 440 with what looks like a Mopar contactless distributor, ballast resistor and chrome ignition module, any recommendations ?

[Pete]

If you keep the Ballast I think from memory you need a 9v Coil (could be a 6v one!!), not a 12v one.

The idea of the ballast is when you crank the engine (Run 2) you give 12v to the coil to maximise the chance of starting.

When you release the Key, you drop to Run 1, which brings the Ballast in to drop the voltage on the coil to prevent it cooking...

It is always better to mount a coil vertically, not horizontally, as they are oil-filled and cooled and the oil circulates better when upright.

[Dave999]

Jensen, at least post 1973 used mopar electronic ignition. orange box i think
hence for a standard setup, a Jensen interceptor coil will work for rpm range to standard redline of the engine

don't let ballast worry you
coils for no ballast just have the resistance built in and are wound to produce a decent spark
coils for use with ballast resistors don't its in a white ceramic block bolted to your bulkhead the coils are wound differently to produce exactly the same spark.
neither is better from a spark point of view
not having a ballast is better from a "fewer things to go wrong" and "fewer connections to corrode and cause problems" point of view. issues that came about well after the original intended useful life of the car (approx 5 years)

the aim here is to avoid running a coil with it built in along with an external ballast resistor as well.... too much resistance too little spark at higher RPM

the reverse is bad as well. running a coil for ballast resistor with no ballast at all. will work but the coil will get very hot and the first thing that fails is the ignition box, or if points they will pit and pip very quickly or weld together. i.e you over burden device that switches the coil off and on

the resistance is there to limit the current that can flow through the coil when the points or ignition module switch it on...think of both of them as switches with a limit of about 2-3 amps for the switch capacity. much like running a 4 bar electric fire with a flex made of bell wire, something burns out quickly if too much current for 1 part of the system flows.


standard moper coil is indeed an 8 or 9 volt coil for use on a 12 volt car... but that confuses everyone so don't depend on the labelling on websites
you want a coil for use with a ballast resistor.

now the fact that you have a chrome box worries me.... if it is a Mopar " chrome" box it will have been specified to work with a specific coil and ballast for drag race only, so part number needed and specific coil will need to be purchased. if it is a standard box or none mopar aftermarket box that just has a chrome case everything above is OK

if its a Mopar "chrome" box i'm not sure, you could try a lucas dlb198 and bypass the ballast resistor this is a middle of the road coil , with some in built resistance to protect your ignition box, for use with electronic ignition and no ballast used on rover v8 equipped cars and i think jag 6 and V12.

i've used both styles of coil on mine and had no problems. even if lucas is the prince of darkness whoever makes their coils for them seems to get them about right.

or junk the lot and get a new kit with ignition box coil and ballast. but that's going to be more than the £25 solutions from your local motor factors, suggested above.

really depends on if its a high compression fire breathing monster or relatively standard, i have suggested solution for relatively standard

Dave

[Dom66]

Thanks Dave,

I suspected it wouldn't be straightforward....

A few pics of the box:

Box & ballast.JPG (99.68 KiB) Viewed 1190 times

C box.JPG (84.6 KiB) Viewed 1190 times

as far as I can read the part number is P4120534.

As most of the coils are oil filled and as Pete says, they are better off mounted vertically, one of the reasons I want to replace....

Coil.JPG (104.39 KiB) Viewed 1190 times

Sadly no markings on the coil.

As far as I know, the engine is stock late low compression other than a 'hemi grind' cam, headers, carb & intake.

What do you think ?

[Dave999]

Ok looks like a mopar chrome box to me

P4120534

supposedly race only but i guess you have proved that to be twaddle in fact i might be getting confused with the gold one


if it is Vintage its probably good i.e made in the USofA rather than PRChineeeya
id suggest you can run standard coil and ballast i.e chase down something for a jensen....


or run a MSD blaster II. its a very low (0.7 ohm) resistance coil so i'd be inclined to keep the ballast resistor for street use

the ballast resistor is. usually 1.2-1.4 ohms resistance

so if you put in a 0.7 ohm coil that's a total of 1.9 ohms (0.7 coil+1.2 ballast) lets call it 2 ohms

and we can work out the current that will flow once its switched on.

approx 8 Volts/2 Ohms = 4 amps max flowing in the coil primary, that seems alright to me

if you bypass the ballast you get the full 12 volts to the coil
12 volts/2ohms = 6 amps probably too much, will knacker the box or burn out the coil


basically you have a robust ignition box that should be run with the ballast you have

MSD blaster 2 is an option it has a primary of is 0.7 ohms therefore keep the ballast

Petonix
flame thrower standard comes in 2 varieties 3 ohm use with with no ballast,
but the 1.5 ohm one use with ballast its kinda in between......

flame thrower ii 0.6 Ohm resistance, keep the ballast

Lucas DLB198 i run one with no ballast it hasn't gone bang yet the cheap option, 1.5 -2 ohm in built so no need for ballast i just joined the wires together with a spade jumper from 1 end of ballast to the other . if it goes bang its 1/3rd of the price of the MSD. it in theory is not low enough on the primary resistance front, to bust your chrome box.

The accel super coil might be ok as well but with the ballast if its low primary resistance

few options


but if you know the primary resistance from the spec sheet of the coil you can work out if you can use it

the lower the primary resistance of the coil the hotter the ballast resistor gets...... keep that in mind also

aim for the middle ground

Dave

[Dom66]

Thanks again Dave,

I'll try and measure the ballast resistance later and maybe splash out on a blaster II

I've looked at the various replacement modules available now, and as well as being very confusing I've been wary that they would all be Chinesium of origin and probably total crap, so I'm keen to stick with the one I have as long as it's working.

[Dave999]

yes if there is nout wrong with it use it as mopar intended
with a ballast and a low primary resistance coil

as with many things it just needs to work the bigger the current the more work you alternator has to do, the stiffer it gets to turn.. and there is a tipping point, you will use a smidge more fuel for the same speed

Dave

[Dom66]

I think I'm past worrying about fuel consumption

I've just measured the ballast resistor, it's a bit lower than your estimate at 0.9 ohm, does that change anything or should I get that blaster on order ?

[Dave999]

I think you will be ok

i'll caveat that with i have no idea what you did to your chrome box in the past
but it was designed for uprated coils and lower Resistance ballasts from 0.5 to 0.9 or the 1.2 -1.4

Dave

[Dom66]

Nice one I'd best go and work out a new mounting bracket to get it vertical...

[Dave999]

vertical for oil filled
if its a solid plastic filled one it make no odds

[Dom66]

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Fitted and running nicely Thanks for the advice

[Pete]

Glad it is all up and running well!

[Captain Chaos]

Hi. Sorry for the thread revival but when I searched this seemed to be the most relevant information.

I had my Road Runner tested on a rolling road yesterday to help with carb set up,more in this a bit later. What reared its head was a misfire I thought was sorted and additionally an overheated coil.

The car was set up for me previously and the ballast resistor was bypassed the reason I was told was that not enough voltage was reaching the spark plugs. I ran the car like this for a while and it certainly felt much better at higher revs. During this period I had a coil fail (Super Stack 8140) and replaced it with an MSD Blaster 2 82023. This coil appears to need a separate ballast resistor and when running with it lacks the power it has when not. It runs a Mopar performance module and electronic ignition.

My coil is mounted in the V longitudinally and I realise this is not correct,yesterday it was suggested mounting it upside down much further forward in the engine bay,I’m with the orientation but the position?

I have NGK BP5S plugs which are new and I replaced what originally the car came with,the tech yesterday suggested that my misfire could be down to these running too hot and detonating,he suggested BP6 or 7 to eliminate this,the misfire was evident at 4800 rpm + but at times did not affect the smoothness of the curve recorded on the machine.

Sorry for so many questions, I must admit to feeling a bit deflated and lost for a direction.

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[Dom66]

I'm not sure mounting the coil upside down is a good idea, I used to have a dune buggy years ago with a Bosch blue coil fitted this way, the previous owner thought it would keep the connections dry. This failed and this is where I was first told that some coils were oil filled and mounting them off vertical was a bad idea...