Coils For K Motors

[GJM85]

I was going to add this to the wiki but ERMA-GERD I got a head ache trying to get it down so maybe another L3370 8URR170 could get it down there. I've been misled for some time due to lack info in regards to coils so would like to pass some information on.

 

 

The majority of stock 3k/4k units are either Bosch or Nippon-Denso oil filled coils designed for use with a ballast resistor.

The ballast resistor is in place to limit the ignition voltage flowing through the coil prolonging the life of the breaker points and leads for that standard and original application, effectively culling 12 volts down to 9 volts.

 

Without going into great detail this is how a replacement coil should be selected.

NB: These Bosch coils are rather cheap and widely known which is why I'm using them as references and not recommending them.

 

* If you want to keep the ballast resistor and points use a Bosch GT40R or equivalent coil.

 

* If you want to remove the ballast resistor but keep the points us the GT40 or equivalent.

 

* If your removing the ballast resistor & the points to convert to a electronic trigger (ie. Hot Spark, Pertronix) use the GT40 or equivalent.

 

* If your using an electronic distributor with internal ignitor (ie. 4k-u,5k, 7k dizzy) use a Bosch MEC 723 or HEC715 or equivalent electric ignition coil.

 

I personally have never seen the electronic distributor with external igniter so I cannot offer suggestion on this. Taking from some info I've read, HEC coils could be too much for the K series electronic distributors and cause premature igniter failure.

 

Any other information anyone can share would be awesome.

 

 

I was using a GT40 with my internal igniter electronic dizzy. I'm looking at a conversion kit for my KE70 points dizzy because it has a better ignition curve. Thorough research, whilst looking for alternatives to the Pertronix recommended Flamethrower, revealed I've been using the wrong coil for some time.

After swapping to an electronic coil, starting, idle and response all improved. Distributor advance still isn't as good as the KE70 dizzy.

Edited May 20, 2015 by GJM85

[altezzaclub]

had to look it up... Ausrotary had a topic on it-

 

High Energy Coil

the HEC are now chinese made and look considerably different

( and yes the original HEC715/6 at high boost/rich mixes/large dwells would crossfire across the posts at the back of the coil )

 

MEC= Medium Energy Coil

these put out less spark energy than the HEC,, but do charge to saturation faster

( ie will be full output at lower dwell periods )

 

I supose this refers to the 5K electronic dizzy with the slow advance curve as stock. Time to change the springs inside!

Distributor advance still isn't as good as the KE70 dizzy.

 

I'm still running the stock coil with the 5K electronic dizzy, so maybe I can make it even better with an MEC 723. Seems fine currently.

 

We used a Hotspark type on the Celica with a GT40. That always worked perfectly.

[Hiro Protagonist]

FYI, there was an internal-igniter electronic dizzy for the 4KEU as well, I had one on my KE55 matched to an Echlin GX-80R coil+resistor

[camerondownunder88]

Hi,

My 3cents...

 

Was said in first post all 3k/4/ units are designed for use with ballast resistor...

 

KE1X cars never had a balast resistor stock so their coils like 12v no resistor out of box.

 

Later coils need to run at the dropped 9V.

 

Also I run a stock 5K electronic dizzy with stock KE1X coil and a mmmm its like a 6AL MSD unit running it in side cabin. 16 sparks at idle per cyclinder and those cheap little spark tests where you wind out the points and arc a gap telling you spark voltage I wind it all the way out and still throw the spark across so thats also a good option. Runs a stock tacho dash in the KE11 and gives better ignition with no coil issues....yet...more energy=more heat I'm sure coils warm but does 1000km a week so far so good 6 months on.

 

Cameron

[rian]

I would also like to add that a GT40 coil can be used with an external ignitor 4K-U electronic distributor.

[GJM85]

I'm not saying any coil won't work with any igniter type. They will. But certain coils are designed for certain types of ignition.

When you get down to the nitty gritty stuff electronic distributors are designed to work with coils of low resistance. A GT40 has a higher resistance of around 3 ohms where an electronic coil can be as low as 0.5 ohms.

 

After Cameron's post I remembered I have a street fire cdi by msd in the garage. Its been a long time since it was in the ke20 and I've sorted out a lot of issues since then. I just put the ke70 bosch dizzy in with the GT40 and hooked up the cdi. I also opened the plug gaps to 1.0mm

I'll see how she goes tomorrow.

Edited April 30, 2014 by GJM85

[GJM85]

In a standard points dizzy 3-4 amps travel across the points when they open. With a cdi ignition it's about 0.2 amps extending their life almost indefinitely.

[GJM85]

The combination worked very well indeed. Great throttle response and plenty of power all the way past 5000rpm.

Looks like I won't be buying an ignition conversion for the bosch distributor.

Edited April 30, 2014 by GJM85

[67Rolla-Ken]

So I'm running a 5K with a 3K/4K Points Dizzy. I have a new GT40 coil but was told it was the wrong coil for her.

My understanding of the above is that the GT40 with no ballast resistor is correct for her. Is this correct?

[camerondownunder88]

So I'm running a 5K with a 3K/4K Points Dizzy. I have a new GT40 coil but was told it was the wrong coil for her.

My understanding of the above is that the GT40 with no ballast resistor is correct for her. Is this correct?

 

If your STOCK KE1X look is STOCK then ditch the resistor.

 

Reasons for balast resistor is at cranking car will drop around 9 volts there is usually a wire from starter system to the coil bypassing the resistor. So as cranking gets 9V. When you start and key is off and starter disengaged then the direct power feed cut and power then goes 12V through resistor then it drops to 9V and coil runs.

 

Resistor coils are designed to work best at the lower voltage. This is so when cranking spark is still HOT. IF they worked BEST at 12V when cranking would be weak spark.

 

KE1X loom is simple and bugger all relays (apart from horn in late models) and thus run a 12V non resistor coil.

 

Reason why I run a CDI is as stated above drops the amps through the points thus they last FOREVER. I found after 6 months the rubbing block on points had worn away so had to reset dwell etc so ditched points for electronic dizzy. But thinking about going back as I have a cam in daily KE11 and electronic dizzy has a shocking advance curve for it.

 

Cameron

[67Rolla-Ken]

Excellent, thanks Cameron.

[GJM85]

Yes you have the correct coil.

Gt40 has a resistance of about 3.2-3.4 ohms.

Gt40R has a resistance of 1.4-1.6 ohms.

Add a 1.4-1.6 ohm resistor to the Gt40R and you get around the same resistance as the Gt40.

 

I measured these two gt coils the arvo and also checked the Mec723 with a primary resistance of 1.1 ohms.

 

My distibutor lead has a resistance of 1.2ohms and the spark plug leads varied from 1.5 to 1.7 ohms.

 

The whole idea behind creating a powerful ignition set up is so you can increase your spark plug gap giving a truely bigger spark.

 

[styler]

For some reason I remember the the ballast resistor coil was for startup not the points???

Basically during startup the battery was drained supplying the starter motor so much a 12V coil wouldnt fire,

so a 9V coil was introduced to aid this problem. Once the motor fired up it was all 12V so the coil needed

a ballast resistor to drop the 12V down a bit for the 9V coil. Hence there are 2 circuits on the ballast style

setup 1) 12V bypass for startup and 2) 9V ballast for running. That's the guts of the theory anyway....

9V coils are for ballast systems and 12V coils for non-ballast systems, not to be interchanged else the car

wont start in one case or it will overheat the coil and burn out in the other case.

 

High performance ignition systems can be used in place of the ballast system as they can overcome the

low battery voltage with a low resistance coil that can fire under the lower voltage and still deliver spark.

I think you connect both circuits for starting and running to this coil for installation after removing the ballast

to enable startup and running functions. The coils get as low as .5 ohm