Gapping the rotor/ cap for stronger spark? - Fuelly Forums

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Old 04-27-2010, 03:43 PM   #1
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Gapping the rotor/ cap for stronger spark?

My Dad says that if you minutely bend the tabs inside the cap a hair away from the rotor, it causes a stronger spark at the plugs. He has been a mechanic for over 40 years, and works in a shop that does emissions. He says that when a car has a miss on a cylinder, and he can't get it to fire right conventionally, he'll bend the tab a hair, and it fires stronger.
He told me this when I told him that I bent mine in a hair, thinking that the spark would be stronger if it didn't have to jump as much of a gap in the distributor.
What do you guys think?
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Old 04-27-2010, 07:09 PM   #2
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I have experienced something like what your dad is describing. This past winter, my 87 civic was missing on cylinder #2 at idle when it was cold. I knew it was #2 because when I pulled the plug wire all the way out of the dizzy cap, the idle speed didn't change BUT- when I pulled the spark plug wire slightly out of the dizzy cap and let the spark jump to the plug wire, it would start firing again, when I pushed it all the way down into the cap where it belonged, it would begin missing again.

I decided that I would increase the gap on that spark plug to try to produce the same effect- but it just made that cylinder miss really bad under acceleration- even after it warmed up (I guess it was OK for idling, but too wide to jump under a load).

Since then, my cold miss has gone away on its own- I think it had something to do with the gasoline in the tank being 6 months old...
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Old 04-28-2010, 04:46 AM   #3
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Seems counter-intuitive. The bigger the gap between the rotor and the cap, the more energy it takes to jump the gap - the more energy that takes, the less energy is less inside the cylinder...

-BC
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Old 04-28-2010, 11:13 AM   #4
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What you may be experiencing is stronger spark from allowing the coil voltage to reach a higher voltage before it jumps the combined gaps of the cap and plug. Remember it is a colapsing magnetic field that produces the spark and if you get the spark to jump further up on the voltage curve closer to the peak energy discharge of the coil you may over power the carbon fouling shorting out the plug with the increased spark power. Kind of like getting a florescent lamp to light up with that initial kick of extra high voltage to get things ionizing inside the tube.
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Old 04-28-2010, 11:17 AM   #5
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Quote:
Originally Posted by JanGeo View Post
allowing the coil voltage to reach a higher voltage before it jumps the combined gaps of the cap and plug.
Would that retard the timing a little, or does it happen a lot faster than matters?
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Old 04-28-2010, 10:02 PM   #6
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Thanks for the interesting info! Right now I have a rough idle, because it's at about 17:1. I'll try increasing the rotor gap slighty, and see what happens.
I'm also interested about the timing. If it actually smoothes the idle, it could be one of those discoveries that everyone can use for free FE increase.
I'll report back when I get a chance to play with it.
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Old 04-29-2010, 04:10 PM   #7
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I used to "blueprint" the cap and rotor on my old VW water cooled CIS Rabbit motors. Seemed to work to make the idle a little smoother, so I'd guess that less energy is being used jumping the distributor cap and rotor gap.

To use this extra energy and optimize the spark plug gap, open the plug gap in .005" increments until you begin get high speed, high load miss, then close the gap .005" from the setting where you just begin getting miss. This is a good all around gap. If you rarely see the top third of your tachometer (driving for FE) just leave it at the setting where you begin getting miss at high speed and load.

Be sure all your ignition components are in good shape, the weak link will fail.

I read about this procedure when I bought a Jacobs ignition coil and wires. It struck me that if that same procedure was used to optimize the stock system pretty good gains might be had without the cost of a $400 coil. Good gains were had without the fancy coil. Oh yeah, you might pick up an extra .5 hp by indexing your spark plugs also.
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Old 04-29-2010, 04:49 PM   #8
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Quote:
Originally Posted by beatr911 View Post
I used to "blueprint" the cap and rotor on my old VW water cooled CIS Rabbit motors. Seemed to work to make the idle a little smoother, so I'd guess that less energy is being used jumping the distributor cap and rotor gap.

To use this extra energy and optimize the spark plug gap, open the plug gap in .005" increments until you begin get high speed, high load miss, then close the gap .005" from the setting where you just begin getting miss. This is a good all around gap. If you rarely see the top third of your tachometer (driving for FE) just leave it at the setting where you begin getting miss at high speed and load.

Be sure all your ignition components are in good shape, the weak link will fail.

I read about this procedure when I bought a Jacobs ignition coil and wires. It struck me that if that same procedure was used to optimize the stock system pretty good gains might be had without the cost of a $400 coil. Good gains were had without the fancy coil. Oh yeah, you might pick up an extra .5 hp by indexing your spark plugs also.
hmmm interesting

i may have to experiment with my chevette. the s10 tho (electronic ign) idle its got an exhaust leak thats constant but every now and then u can see the engine kinda shake a little more and hear the leak spudder for maybe 1/3 sec. the trucks always had a random cyl 2 misfire code too. ive tried different coil packs (off a cavileer unknown year) same issue. has new plugs and wires too(about 15k ago on wires, plugs about 35k ago but regapped/checked to .060 about 15k ago when i did the wires)
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Old 05-05-2010, 10:16 PM   #9
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Tonight I opened the gaps between the rotor, and distributor a tiny bit, and it idles more smoothely. I still don't understant it. My roommate, who is an engineer at Intel said something about it drawing more power. I wish I understood electricity better. Anyway, it runs better now, but I didn't drive it much.
I have indexed my plugs, but the configuration is a "Hemi", so it doesn't make much difference.
Now it makes me wonder if opening the gaps more would be helpful.
I can never leave well enough alone. I'm like "Tim the toolman". Arr-Arrr.
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Old 05-20-2010, 04:49 PM   #10
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Dig up a copy of:
The Doctors's step-by-step Guide To Optomizing Your Ignition
Dr. Christopher A. Jacobs, PhD, E.E.
Jacobs Technical Publishing
ISBN 0-9650856-0-0

He discusses the kind of stuff race engines use.

Gap your plugs until the performance drops off. I use MPG as the measurement.
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