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Best Ignition Leads to compliment the Classic Retrofit CDI+ box


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11 hours ago, Jonny Hart said:

I run the non-braided Beru ones and probably 8 years old now.  They were bought before the distributor cap end sizes went 'wrong'.   When I got them, I unscrewed the plug caps and made sure the brass 'screw' was in the centre of the lead touching the conductor( they weren't).  I don't run the braids because they encourage degradation of the wire insulation (which acts like a capacitor dielectric) and you end up with lots of stray sparks in the engine bay.

Regarding solid core versus carbon, basically solid lasts longer (than carbon) and carbon produces less EMI (interference) on newer cars.  

The resistance of the lead is irrelevant on an SC, since it has 5kOhm in the rotor arm and another 3kOhm in the plug cap.  Those resistors are doing the EMI suppression so you don't need resistive wire.

Hi Jonny,

Thanks for that. Its great to get an informed opinion on the braiding.

Based on what you have said braiding could actually hide an insulation problem too if the insulation breaks down and the sparks are taken straight to ground in the braiding and are not as visible ?

Is the 930 rotor arm the same as the SC in having a 5k resistor inset in the resin ?

Regards

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55 minutes ago, carrpet said:

Is the 930 rotor arm the same as the SC in having a 5k resistor inset in the resin ?

 

Yes, it has ballast resistance although I’m not sure if it’s 5k. I removed this on my rotor arm to work more reliably with the box. Here is my 930 modified arm. Not pretty but has stood the test of time. 
 

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David

Edited by flatsix777
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1 minute ago, flatsix777 said:

Yes, it has ballast resistance although I’m not sure if it’s 5k. I removed this on my rotor arm to work more reliably with the box. Here is my 930 arm modified arm. Not pretty but has stood the test of time. 
 

A80F932F-D728-4235-BCAA-0C53165DA326.thumb.jpeg.5f62a5c4110d8b1f365ea9f805f45d3a.jpeg

Well it won't win a beauty contest David but I get it !

Is this reliability problem to your specific type of CDI+ box ? Did the manufacturers recommend this course of action ?

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The standard rotor has the ignition rev limiter built into it, which could give a mis-fire when old.  If you use Jonny's CDI+ box, an option is to use the later 3.2 (non-rev limiting) rotor arm and rely on the soft and hard rev limit options in the CDI+ software.

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5 minutes ago, PeterK said:

The standard rotor has the ignition rev limiter built into it, which could give a mis-fire when old.  If you use Jonny's CDI+ box, an option is to use the later 3.2 (non-rev limiting) rotor arm and rely on the soft and hard rev limit options in the CDI+ software.

Fascinating ! How does the rev limiter work ?

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11 minutes ago, carrpet said:

Fascinating ! How does the rev limiter work ?

It works by cutting alternate sparks.  This gives a much less abrupt limiter, rather than throwing you through the windscreen.   Much kinder to engine since it keeps the fuel burning, thus avoiding a backfire when the ignition comes back in. 
 

You can use the 3.2 rotor arm or you can just take the spring and plastic plunger out of the SC/Turbo one.  Arguably this is a better solution as it retains the 5k ohm.  The 3.2 rotor is 1k.

I think David has removed his resistor due to having an MSD box.   The MSD unit is known to burn out the rotor resistor.   CDI+ won’t do that since it is designed to work with the 9k ohm total resistance across all Porsche CDI cars.  

Edited by Jonny Hart
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4 minutes ago, Jonny Hart said:

It works by cutting alternate sparks.  This gives a much less abrupt limiter, rather than throwing you through the windscreen.   Much kinder to engine since it keeps the fuel burning, thus avoiding a backfire when the ignition comes back in. 
 

You can use the 3.2 rotor arm or you can just take the spring and plastic plunger out of the SC/Turbo one.  Arguably this is a better solution as it retains the 5k ohm.  The 3.2 rotor is 1k.

I think David has removed his resistor due to having an MSD box.   The MSD unit is known to burn out the rotor resistor.   CDI+ won’t do that since it is designed to work with the 9k ohm total resistance across all Porsche CDI cars.  

Sounds like I ought to get that serial interface working to connect to your box of ever growing tricks Jonny !

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46 minutes ago, Jonny Hart said:

I think David has removed his resistor due to having an MSD box.   The MSD unit is known to burn out the rotor resistor.   CDI+ won’t do that since it is designed to work with the 9k ohm total resistance across all Porsche CDI cars.  

Exactly, I knew about the reliability issue with MSD boxes in our cars so did the fix from the off. No problems at all. 

David 

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3 hours ago, Jonny Hart said:

It works by cutting alternate sparks.  This gives a much less abrupt limiter, rather than throwing you through the windscreen.   Much kinder to engine since it keeps the fuel burning, thus avoiding a backfire when the ignition comes back in. 
 

You can use the 3.2 rotor arm or you can just take the spring and plastic plunger out of the SC/Turbo one.  Arguably this is a better solution as it retains the 5k ohm.  The 3.2 rotor is 1k.

I think David has removed his resistor due to having an MSD box.   The MSD unit is known to burn out the rotor resistor.   CDI+ won’t do that since it is designed to work with the 9k ohm total resistance across all Porsche CDI cars.  

Yes I checked the resistor as 5k ohm. I will take a look at removing the spring and plunger !

 

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15 minutes ago, Ian Comerford said:

I guess I should do this too.  Also better read the CDI+ instructions to understand the setting of the limiter

Yes that would make sense ! Do you know anyone who knows how to use a serial interface??

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7 hours ago, Jonny Hart said:

You can use the 3.2 rotor arm or you can just take the spring and plastic plunger out of the SC/Turbo one.  Arguably this is a better solution as it retains the 5k ohm.  The 3.2 rotor is 1k.

For a simpleton like me, whats the impact of running the 3.2 rotor Jonny? 

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6 hours ago, carrpet said:

Yes that would make sense ! Do you know anyone who knows how to use a serial interface??

Perhaps, just plug in the USB cable that comes with the unit and run the software?  

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3 hours ago, Northy said:

For a simpleton like me, whats the impact of running the 3.2 rotor Jonny? 

None really.   Slightly reduced EMI suppression but negligible and we aren’t really radio listeners now, are we?
 

Some tech info:

https://www.vishay.com/docs/30255/an0004.pdf

Edited by Jonny Hart
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10 hours ago, Jonny Hart said:

Perhaps, just plug in the USB cable that comes with the unit and run the software?  

I am just winding up my next door neighbour Jonny !

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So it looks like the following recipe might work with a Classic Retrofit CDI+

Instate rev limiter on CDI+

Disable rev limiter on rotor arm but retain the 5 kohm resistor

Use high quality after market leads with excellent (silicone ?) insulation

Sounds like earthed braiding is no longer necessary and has possibly had it's day ? It may cause the insulation to fail more quickly due to the capacitor dielectric effect.

Edited by carrpet
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