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Old 04-02-2008, 11:13 AM   #1
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Default COPS + Boost + Fuel = Spark GAP?

I've been reading up on the relationship between the 4. I believe what I'm finding is that it's preferred to run as big a spark gap as you can without blowing the spark out with fuel.

In boost, we're running rich and the potential is greater for having the richness agrivated by a bad spark. Either a spark gap so wide that it's that the energy isn't concentrated enough to fully combust... or a gap so small that the spark itself isn't big enough to reach all the fuel. The fuel is either blowing out or overwhelming the spark? (I KNOW that's pretty retarded kindergarten speak, but am I close?)

In any case, the dyno operator last weekend was concerned that my plug gap might not be right due to my high-boost and relatively low power. We discussed my spark table and he thought there was room for improvement. We also discusses that my T25 was practically out of steam.

I think I'm gonna pick up at least another 10-15whp with the new Paul-Hybrid (or maybe not now due to new discussion in the dyno-tuning thread) spark table... and I was wondering what to do about the gap now that I've got COPs.

I'm running the standard NGK 1-step colder and was wondering if the COPs provide enough of a better/stronger spark that it would be worth it to widen my spark plug gap? What would I see happen? I'm thinking that better combustion would lead to more fuel being burned which would lower the 02 in my exhaust and I'd start showing a rich condition... which would allow me to add less fuel? Better mileage and more power?

What is the relationship between Spark Plug Gap and fuel in an FI engine when you upgrade the igntion system? What are my options?
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Old 04-02-2008, 11:36 AM   #2
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the biggest gap you can get away with will provide the best spark. Most people here are getting away with the stock gap, 11mm, with cops with up to 17psi of boost.
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Old 04-02-2008, 11:38 AM   #3
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I was ok at .040 gap (slightly less than stock) with summer blend gas and the cops at 17.5psi over atmo. Stock spark blew out around 8psi or so.

I personally hate cold plugs, and am running factory spec plugs, a decent sized intercooler, and a dyno tuned spark map.
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Old 04-02-2008, 11:49 AM   #4
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lets see...

a spark plug works by ionizing the mixture between the electrodes. this heats it up. the longer the spark, the more heat you're putting into the system (across a larger area).

so the goal is complete combustion--ie enough heat to ignite the whole mixture in the chamber. that gives you more power per unit volume of fuel because you're converting more into mechanical energy.

the COP setup will provide more energy to the plug so you can widen the gap compared to the stock system but you will reach one of two limits:

1. the point of diminishing returns (no benefit to increasing the gap more)
2. too large a gap for the given cylinder pressure (spark "blowout" or misfire)

a smaller gap will be easier for the coils to ignite but isn't as hot and risks incomplete combustion.

I bet you hit 1 before you hit 2 below 20 psi. start with .040 and go from there. if it misfires, drop it a couple thou.
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Old 04-02-2008, 01:32 PM   #5
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Matt, someone told me a couple of days ago that too large a gap will eat plugs. T/F?

Sam, I'm at .024 on stock coils right now and I hate it. I plan to bump to .040 when I do COPs and not play with it any further.
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Old 04-02-2008, 01:59 PM   #6
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heat eats plugs. i suppose running a large gap on a hot plug could erode the electrodes faster than normal, but they will wear away over time anyway. detonation/preignition will kill them fast too.
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Old 04-02-2008, 02:00 PM   #7
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I'm on .025 on stock '99 coils, it was blowing out at like 9 psi with .035 gap. Be nice to get COPs installed one day.
Anyone have 2 cops laying around?

Considering how cheap plugs are, would it kill you to check and replace them during oil changes if they really are bad. We're not driving 100 hp cars anymore, an extra $8 every other oil change would be cheap preventative maintenance.
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