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Distributor, Ignition, Coil, Spark Braindump?

Super Jamie

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I'm getting into the wiki again and it's gotten a bit messier from when it was the old FAQ. I'd like to tidy it up and take the chance to include even more knowledge while I'm at it.


We currently have three pages for distributors and ignition:


http://www.rollaclub.com/wiki/index.php?title=Tech:Engine/K_Series/Distributor'>http://www.rollaclub.com/wiki/index.php?title=Tech:Engine/K_Series/Distributor - this is pictures and part numbers of internal and external ignitors


http://www.rollaclub.com/wiki/index.php?title=Tech:Engine/K_Series/Electronic_distributor - this one i tidied, rewrote, and added to today


http://www.rollaclub.com/wiki/index.php?title=Tech:Engine/K_Series/Distrib - this one is just denso part numbers


I'll combine these into one page.


If anyone has anything at all they'd like to add on the topic of dizzys/ignition/coils/spark, please note it down in this thread, I'm happy to organise it all into a nice wiki article.


Some things I can already think to add:

  • Talk about Denso and Bosch points distributors, list differences (Denso adjuster screw) and cap/rotor part numbers
  • List coil wire lengths and plug types, I have this in a picture I saved off eBay
  • Talk about how lower resistance of plug wires is the most important factor in wires, not shielding thickness
  • Upgrading oil-type coils, from stock to Bosch GT40 to MSD Blaster II
  • Talk about having distributors regraphed to suit different cams, give props to PEI in Nunawading, Vic
  • List stock spark plug numbers and gap
  • Talk about the need to run cooler plugs in a worked K motor or your tappets heat up and unwind clack clack clack :P

Things I can think I'd like others advice on:

  • Ballast resistors, wtf they even do, how they seem to be common problems, how to diagnose a faulty one
  • Where did the elec dizzy with external ignitor come from? Late or import KE70? 5K vans? Other?
  • Any experience on running fancy $200 spark plugs in K motors? Worth it or waste of money?

If you'd like to talk to any of these points, or corrent me, or can think of stuff I've missed please do go for it!

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Ballast resistors... they drop the voltage from 12V to 9V to suit the 9V coil that Corollas have. When you hit the 'start' part of the ignition key it cuts the ballast out of the circuit and feeds 12V direct to the 9V coil as the starter cranks..


This is good because the starter is dragging hundreds of amps out and the voltage has dropped to that anyway. Now your coil is working at 100% to fire the motor, instead of 75% in a non-ballasted car.


As soon as you let the key back from 'start', the ignition feeds through the ballast and the coil runs on 9V while you drive around. The wire in the ballast gives the extra voltage off as heat, just like a old lightbulb used to, and that degrades the wire. Eventually they burn away and I assume the car will crank but not start. My two KE70s have resistances of 3.2 and 2.7ohms.


My Haynes manual doesn't list a value for them, and in fact it doesn't even aknowledge the ballast resistor exists. it has no trouble-shooting ideas about it or listing of a possible fault in not starting! I can see it in their photos...


In the Wiki it says this Jamie-

will need to be changed to a non-ballast High Energy Ignition coil which suits an electronic ignition module.


Which I haven't done. I've just hooked the electronic dizzy feed to the ignition side of the ballast resistor. This means it sends 12v to the electronic dizzy when running, but only 9V when cranking as that wire is live from the coil +ve back through the ballast. It just seemed to be the handiest thing at the time!


So should I hit the wrecker on Monday for a Commie one?

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Ballast resistors... they drop the voltage from 12V to 9V to suit the 9V coil...


Ahhhh! Many thanks for the writeup, that's super useful, I will include that for sure!


So should I hit the wrecker on Monday for a Commie one?


I would hey. I've heard oil coils work for a while, but eventually burn the ignitor out, then you're up for a new ignitor.


I am pretty sure the Bosch HEC716 (Commodore coil) is the same thing as the Bosch HEC715, except the 715 has a socket so you don't have to change the center plug lead. Looking on eBay the HEC715 comes from:


- Sept 1985 to Sept 1987 Ford Telstar AS 2.0 TX5 EFI and EFI Turbo

- June 1983 to Jan 1985 Nissan Bluebird 2.0 L20B

- Also for use with Microtech direct fire LT series ECUs

- Common upgrade for 13B rotary engines with electronic distributors and twin coils


I just learnt about this HEC715 coil this arvo but it seems to be a good choice too.


The ausrotary thread on the HEI coils says the terminals are not marked positive/negative, but apparently it doesn't matter which way you wire them? If you get one, let us know how you go plugging it in.


If the wrecker wants heaps for one, there's a VS V8 coil on eBay for 10 bucks at the moment. There's also various OEM replacements for $30 to $90. Microtech sell a set of 4 coils for $250.


Oh, and I don't think you need the ballast resistor at all with a HEI coil. These are all 12V ignition parts.

Edited by Super Jamie
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Wear on the 3k distributor camshaft causes issues with the mechanical advance.

Something to look out for.

The posts on the advance weights get stuck and it doesn't return to initial advance properly. Or it gets stuck when your setting your initial timing and limits your maximum advance.


Edited by GJM85
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Standard Top Gun 8mm leads have a resistance of 1.5k ohms.

Bosch Super leads are 1.3k ohm. They're about an inch shorter than the top gun leads.

Coil to dizzy leads resistance can be minimised by shortening it. They always seem a tad long.


Lead thickness is increased to suppress radio frequency interference (RFI) between the ignition system and other electrical components like the stereo.


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  • 1 month later...

Something in regards to the electronic distributor with inbuilt ignitor. They've got two ding dangs on the vacuum advance unit


On my particular distributor which is a Nippon Denso original recently rebuilt by Performance Ignitions, the dinger on top pulls 10 degrees advance and the dinger on the front pulls 15 degrees advance.


Which do you use & where do you source the vacuum? Manifold or ported/timed vacuum?


On a stock or slightly modified engine with good idle vacuum the vac advance unit can be used to boost take off and low end throttle response. Increasing low end torque and fuel economy at cruise speed. For this ported vacuum, also known as timed vacuum, is tapped from a lower vac port on the carburettor just above the primary throttle plate. As the throttle begins to open, engine vacuum pulls the advance unit diaphragm adding timing degrees at take off or part throttle.


On highly modified engines, with larger camshaft profiles and poor idle vacuum, the vac advance unit can be used to boost idle vacuum by adding degrees to the engines idle advance. For example.

An engine with a 270 advertised duration camshaft, or more, will suffer a dynamic compression loss at idle causing inconsistent and unreliable idle or engine hunting, excess engine loading and poor fuel economy.

Using the vacuum advance to pull extra timing at idle will do amazing things for you.


Here's the benefit of the two ding dang advance unit. I use manifold vacuum on the front stem to pull an extra 15 degrees assisting at idle, 10 degrees static +15, and I use the ported vacuum on the top stem to pull 10 degrees advance on take off and cruise assisting with throttle response and fuel economy.



Edited by GJM85
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I dug out a HEC715 recently, can check for markings if you like.


My old man always used to tell me the resistance of plug leads wasn't that crucial, but I can't remember why. He's an electronics guy, so it probably made sense.


Also, a few people a while back were doing elec conversions with an aftermarket setup, was it hotspark or something? Might be worth talking about that as K parts get rarer.

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My old man always used to tell me the resistance of plug leads wasn't that crucial, but I can't remember why. He's an electronics guy, so it probably made sense.


More resistance in ignition components creates a higher current draw on the vehicles electrical system. The theory being, the higher the current requirement, the shorter the part life.

Taking away the 'fine tuning' concept, spark plugs & leads will either work or they won't.

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Sure, I think the explanation was probably along the lines of, given the incredibly high voltage and the resistance caused by the other components of the system, dropping a few k (resistance, not money ;) ) in the wires really isn't money well spent. As you say, it all either works, or it doesn't.

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