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plug gap with Pertronix


Hans

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Taken from http://www.pertronix.com/support/tips/#a5

 

What should I gap the spark plugs to?

The Ignitor has no set specification in which the spark plugs should be gaped at. Every engine responds differently to spark plug setting. In most cases increasing the factory recommended gap by .005 improves the engine performance.

 

rtheriaque wrote:

Carbs: They're necessary and barely controlled fuel leaks that sometimes match the air passing through them.

My build blog:http://www.bmw2002faq.com/blog/163-simeons-blog/

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Not too big- .028"?  The blue coil's not very high output.

 

Spark gap depends quite a bit on both coil voltage and current.

 

hth

t

 

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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Blue has worked well for me- just make sure not to use resistor plugs, rotor AND wires in the same car!

 

While having an arc welder in every cylinder SOUNDS like a neat idea,

there's not a lot of performance gain from it- far less than from good timing,

good timing control, good mixture, a clean air filter, etc.

The blue coil's hot enough for a street car...

... at least, it has been for me...

 

t

 

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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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2 hours ago, TobyB said:

just make sure not to use resistor plugs, rotor AND wires

 

don't use an external resistor either, whether it is the ceramic style, or the resistor wire found in later cars.

 

blue coils have the resistance built into them.

 

I use the NGK BP6ES (no R), although I am not Really suRe what diffeRence it makes.


Tom

     DISCLAIMER 

I now disagree with some of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book. 

I've switched from using ported-vacuum to manifold, with better results. 

I apologize for spreading misinformation.  

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If you have the 5k Botch rotor, the R plugs, and higher resistance ("suppression") wires with the blue coil,

you'll possibly get misfire under heavy load.  There's simply too much resistance in the secondary circuit.

A 1k Bremi rotor and non- resistance plugs solved the problem.  Kept the wires.

 

Long time now.

 

t

 

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Hmmm. More variables. I ended up with R plugs. Wires are Bosch Ultra Premium; no  clues on suppression value. New non- rev limiter Bosch rotor on order. How Does one determine resistance?

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On 5/27/2018 at 9:30 AM, Hans said:

New non- rev limiter Bosch rotor on order. How Does one determine resistance?

use an Ohm meter between the contact in the center of the rotor and the tip.

Bosch usually puts a number on the underside of the rotor.  (R1 or R5)

035.thumb.JPG.5a4e4a0e976661ddc8e4131f1684395e.JPG

The stock style is 5K (R5).

I use the type with the wider tip, which is 1K.

I believe they were stock on e21 cars.

 

034.thumb.JPG.126ec33e1eb7c5207c4e18b02a132f3e.JPG

EDIT-- I've gone back to the R5 rotor with 5K ohm resistor.  I read that it increases the duration of the arc at the plug.  R5 is the stock rotor.

 

 

 

Edited by '76mintgrün'02

     DISCLAIMER 

I now disagree with some of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book. 

I've switched from using ported-vacuum to manifold, with better results. 

I apologize for spreading misinformation.  

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I have seen where people grind out the epoxy/resistor and solder in a fat piece of braided copper wire, then re-epoxy over it.

 

VW guys, I think.

 

Yup, found it.

You could do this with a wide tipped rotor and it'd be custom.

I can't say for sure that it is smart, but it looks like fun.

TOm

http://www.huelsmann.us/bugman/RotorTech.html

     DISCLAIMER 

I now disagree with some of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book. 

I've switched from using ported-vacuum to manifold, with better results. 

I apologize for spreading misinformation.  

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I've done that.  Both of those things, in fact.

 

Napa used to sell an Echlin branded rotor that was a solid copper bar with a wider tip.

Haven't tried to find one recently- it was in their interchange for a 2002.

 

I have used the Bremi 1k successfully with an MSD and an Accel yellow coil-

the coil makes a big difference, too.

 

https://www.rockauto.com/en/catalog/bmw,1972,2002,2.0l+l4,1010732,ignition,distributor+rotor,7136

 

Looks like Standard makes one, too.  Narrower tip, tho.  And kinda not- sexy- lookin'

 

t

 

 

GB-381photo primary__ra_p.jpg

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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As for the gap, my car has a Pertronix Flamethrower and won't even run at the stock plug gap, but I found it runs well at .038.

1969 2002

Doubles as a work bench and lunch table

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I stumbled across this information I posted a couple years ago (but had forgotten).

 

Here is what Hank had to say about that in 2001 on a Mopar site:

HankL
10-04-2001, 11:28 AM
As I understand engine combustion theory - a large spark plug gap would be slightly more prone to pinging than a small gap for the following reasons:

1. The small area of fire around the spark is called the 'kernel' by automotive engineers. A bigger sparkplug gap inherently creates a bigger kernel. This bigger kernel not only starts bigger but grows 8 times faster, because of what is known as the 'Volume Power Law'. The Volume Power Law is a fancy way of saying "If you make a ball shaped thing twice the diameter it will contain 2x2x2=8 times the volume inside. 
What this means in practical terms is that making the sparkgap bigger is like slightly advancing the ignition timing. More ignition timing increases the chance of detonation/pinging.

2. Bigger sparkplug gaps are harder for the ignition system to get a spark to jump across. This is especially true at high rpm, (like above 3500 rpm) and at wide open throttle. So a too-big sparkplug gap can cause a missfire at high rpm and wide open throttle. This missfire will show up first as very slight and intermittant, and gets worse as the rpm goes up. Unfortunately at high rpm there is already more noise and vibration naturally, and it is sometimes hard to detect the slightly greater vibration that the truck driver normally uses to spot missfires. 
A slight missfire can cause a ping. What happens is this: after a missfire the next filling of the cylinder is much greater because there is not the normal left over exhaust gas that is normally there. Instead of getting 80% fresh mixture in like a normal filling of the cylinder - that cylinder now gets 100%. Normally the 20% left over exhaust gas slows down burning ( like EGR pollution valve schemes) but now the burning is even faster with 100% pure mixture. This 'supercharged' situation results in detonation pinging that the truck driver hears as an intermittant ping.

If you read the engine books that most experts write - they tell you to start with a small sparkplug gap and gradually increase it with caution. 

Many ignition experts (and sparkplug websites) warn that beginners think 'bigger is always better' and use too big a gap. High rpm engines with high compression and/or supercharging need small gaps. Larry Widmer recommends gaps of 0.020 to 0.035 in ultra high performance applications - even with MSD systems. Widmer has done the design/porting on at least one version of the racing cylinder heads used on the current Dodge Nascar V8.

When in doubt - set the gap smaller. Also remember that the gap grows bigger with wear and mileage.

 

I was chasing pinging and reducing the plug gap seemed to help.  Yesterday I checked my plugs and they are looking  little worn, but not yet toast.  (NGK BP6ES)  The plug gap was .030" and I set them back to .024".  I have a stock coil, points/condenser, 1K rotor.  

 

Since points and Pertronix are basically switches, I don't see how using one or the other would affect the plug gap.  Stock coil, stock gap.

 

I think there is a notion that bigger gap means more hOrsepOwer, sort of like more AdvAnce means more hOrsepOwer. 

 

Another thing I read is that increasing plug gap increases resistance, which stresses the ignition components and they will crap out sooner.  

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     DISCLAIMER 

I now disagree with some of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book. 

I've switched from using ported-vacuum to manifold, with better results. 

I apologize for spreading misinformation.  

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