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will an ultra coil fry my matchbox dizzy?


.sunlover

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The matchbox coil has a resistance of .8 to 1 ohm resistance. A lower resistance coil will draw more current through it which could 'fry' the matchbox module. I would guess .75 ohm would be fine.

 

Higher current flow equals higher output voltage but it's rough on the points or electronic modules. It also over heats the coils too. Everyone likes to show off their 50,000 volt Whiz Bang, super duper, Firestorm, lazer beam, Death Star, Lightning Strike coil. But in reality the plugs never fire at 50,000 volts.

 

The magnetic field collapse that generates the high voltage is not instant and takes a finite amount of time, short, yes but measurable. The high voltage output starts at zero and builds up towards maximum. On an idling engine very little voltage is needed to fire the plug, under 10,000 volts. When the voltage reaches the breakdown point of the air gap on the plug it begins to arc. Voltage cannot rise any further because there is now a path to ground through the bridged plug gap.

 

Full throttle with maximum cylinder filling increases the gap resistance and the voltage must rise much higher to begin arcing. Perhaps 15-20,000 volts. Higher compression motors perhaps 25,000 volts. Turbo or SC motors with extra cylinder filling even more 28-30,000 volts. What about the extra 20,000 volts left over you ask? (30,000 on a stock motor) Well it's there potentially, but not used.

 

You could increase the plug gap slightly to force a higher voltage arc. In fact this is what Nissan recommends with their EI dizzys. Normal points gap is about 0.032". EI plug gap is 0.038 to 0.042". A wider gap presents a longer fatter spark for lighting the fuel/air mixture. The problem with forcing a higher voltage is that it will always look for the easiest path to ground. Instead of the plug gap an old wire set, cracked cap or damaged coil will start to look easier.

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Mike, do you know the coil resistance values for a late model Nissan coil? Like used on all of the mid 90's cars and trucks?

 

I was using one with my matchbox dizzy, and it worked great. Just didnt know if i should have been using it.

 

I've used one of the 720 dual coils no problem. I don't know the values but you can simply borrow a multi-meter and set on resistance and measure them yourself. Around 1 ohm should do the trick.

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Oh...... thank you :) I don't want to fry my dizzy and go through more caps and rotors for a chance at a finite upgrade in combustion.

 

Well it's obvious you should have more voltage than you need but 3 X is a waste. If you have it and it's the proper resistance then for sure run it, no harm done.

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what you have beside I have this coil?

Point w ballst resisitor?

match box?

Pertronix conversion?

ect.......

this does help

 

 

Never run a .7 or .75 ohm coil with POINTSS

 

If Matchbox then its fine but really the stocK Jap EI coil is propably better

 

 

People should not put on Coils just to put them on. See alot of cars go bad due to BLING!!!!!!!!

 

 

It is in the title Hainz. Matchbox.

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  • 2 weeks later...

I'm convinced I've got the wiring wrong since I installed my matchbox. After about 20 minutes of hard driving I'll get on the gas and the engine will sputter at about 4 grand (rpm). If i squeeze the throttle slow its not as bad. I experiment with running the resistor and not running it. With the resistor it hesitates from idle to full throttle, without the hesitation goes away, but the sputtering comes back after some driving and high rpm. Hope I'm not hijacking the thread... any advise?

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If you have to put resistance on the coil then why bother with it? Might as well have a stock one that works just as well. About .75 to 1.1 ohm is used with the matchbox module.

 

That's the funny thing I asked for the coil that went with the matchbox distributor I bought, I got one with a resistor. They said that's what came on the truck? So maybe I'm in the market for a after market coil? One .75 to 1.1 ohm. Hmmmm if that's what it takes to take advantage of the matchbox I will do it. I just want it to run correctly is all, I'm not looking for performance any more. Oh that brings up the spark gap, I'm running what ever stock is. I can open it correct...to what? Thanks Mike.

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Take it back. You want a coil from any '78-'79 620/HL510/200sx or an '80 720 truck with L20B motors. The coil is intended for use with the matchbox and is used without a ballast resistor. You can use the older coils with a resistor but you won't be able to take advantage of the higher output.

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I have a question, I have a matchbox dizzy with a stock dizzy coil, I am gapping the plugs at .032 and there is the slightest ping/pinging every once in a while, if I gap them at .040, will/could that change anything?

 

If you have a matchbox distributor with the stock points coil and ballast stay at 0.032". Some motors will ping very slightly when mashing the gas at low speed and you can forget it. If constant, then damage will result. You could try backing the timing a degree or two or maybe change where you get your gas.

 

If you can find an EI coil you can use that instead and get rid of the ballast resistor. Your output will be higher and then you can go to 0.038"-0.042" gap.

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If you have a matchbox distributor with the stock points coil and ballast stay at 0.032". Some motors will ping very slightly when mashing the gas at low speed and you can forget it. If constant, then damage will result. You could try backing the timing a degree or two or maybe change where you get your gas.

 

If you can find an EI coil you can use that instead and get rid of the ballast resistor. Your output will be higher and then you can go to 0.038"-0.042" gap.

 

I have an El coil, that is what I meant by "stock dizzy coil", at least I beleave it is one, I guess I have never checked it to find out, if I can find marks on it I will post them. As for the gas, unfortunatly I use regular, as I buy so much gas a month for the business, i just can't rate ethel. If I do have a dizzy coil, will changing the gap change anything, or should I just dial back the timing a degree?

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Alright, ollz, jacking this thread back ;) , this is an oik of mine, a later model ultra coil, and I an only seem to find specs for the new model, and heard it was .8 and up twice, and .2 to .4 at another site. even pointing me in the right place to look for this particular model ultra coil would be a great help. I do plan on gapping the plugs bigger. My replacement dizzy (or something else related) also poops out a bit at high rpm's too, but I thought I remembered getting the 79 620 coil to be right for the matchbox dizzy, but who knows what the parts guy grabbed me. I do believe my plugs are gapped for the 79 as well, but it's easy to check. I had a 4 year frustration period where I was stumped and very busy learning everything about Semi trucks, engine and body, also learning a few things that apply to datsun mechanics as well. Turned out the fuel tank treatment hadn't set all the way, and was contaminating my new fuel system, making it run like a hooptie, and eventually letting the tank finish rusting through.

 

2011-09-18221433.jpg

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  • 2 years later...

I've got a '77 620 and I just picked up a matchbox dizzy from a '79 620 to swap from the old points. Got it wired up and double checked everything but it doesn't have any spark.

 

I did quite a bit of research h and made sure I wired it up right and the only thing I found that might be causing it is I still have a pertronix 1.6 ohm coil wired up to it and have power to the distributor but no spark.

 

Could it be that I need a lower ohm coil?

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Ok so it failed step 6 of the matchbox test. It says "Voltage more than 1V below Battery cranking voltage from Step 2 (or below 8.6V). Check ignition switch, fuse and wiring"

 

I got almost no voltage so I'm pretty sure that means it failed. I know the ignition switch is good because it started ok with the points dizzy but what fuse and wiring is it talking about? Is it just talking about the fuse box fuses under the dash or something else?

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The wiring is the Ignition wring - to the coil from the harness and includes the ignition switch. Points use two wires from IGN switch. Make sure both are connected to the EI system or you may have 12v in ON but not in START.

 

The fuse it is talking about is in the Fuse Box. Check them all.

 

 

 

Background. Step 6 is checking the supply voltage. It is not a test of whether the module is good or bad.

 

Failure means a wiring problem

 

Step 6 Power Supply (Cranking)

 

1. Pull coil wire from cap and ground it

2. Set Voltmeter to 20V DC scale

3. connect Voltmeter between distributor case and the "B" connection (stem of T)

4. Crank engine (key at START) and observe voltage

 

 

Results:

° Voltage more than 1V below Battery cranking voltage from Step 2 (or below 8.6V). Check ignition switch, fuse and wiring

* Voltage close to battery cranking voltage from Step 2 (no more than 1V lower) AND better than 8.6V. This test is OK. Proceed to Step 7

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