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Discussion Starter #1
I recently bought original spark plugs (NGK) for my 2012 altima and they were supposed to be gapped at the factory at 0.044. However, when I installed them I noticed that the car was rough idling and the engine was noisier than normal. I decided to check the gap and they were actually gapped at 0.041-42. I corrected the gap to 0.044 and the engine is running better. I then decided to run a little experiment and set the gap at 0.050 and the engine is even quieter.

My question: would increasing the gap even more (like to 0.055) have any detrimental effects on the car (ignition system, coils, etc.)?

Thanks.
 

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09 Altima 3.5SE 6MT Sedan
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More gap = Higher Voltage

So you are forcing your coils to work harder to make the spark...probably resulting in reduced lifetime.
 

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Discussion Starter #3
Thanks for your reply....

Are you referring to reduced lifetime on the coils, the cables, the spark-plugs, something else? If so, are there any sings that I can check for to see if any if these components are being overtaxed?
 

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09 Altima 3.5SE 6MT Sedan
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Not that I know of...basically the system is designed for a 0.044" gap so...

As a rough rule, spark voltage = 3KV * gap in millimetres. So 0.044" x 25.4mm/inch = 1.11 *3,000 = 3,300V (give or take)

If you stretch that to 0.055...you'd be asking those coils to hit 4,200V each time or almost 1,000V higher than their insulation is designed to take. We don't have plug cables in these VQ/QR engines, but your spark plugs may also deteriorate faster with the more energetic spark.

Why? He asked. If there was some secret to bigger gaps, why would they not take advantage of it at the factory?
 

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Discussion Starter #5
Ok,it makes sense, but I wish there was a way to tell that the coils are being overtaxed (in terms of voltage). Although these altimas do not have cables, they do have coil-packs and I've installed new boots on it (the ones that attach to the coils).

Regarding the "secret to bigger gaps" and taking advantage if it at the factory, I read this online (which is what got me started on this gap issue):

Spark Plugs: Increase The Power of Your Ride

If you search on that page for "the car manufacturer's recommended spark plug gap is not optimal! " you will find the paragraph that talks about customizing the gap.

Thanks.
 

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09 Altima 3.5SE 6MT Sedan
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Classic engineering dilemma. I see it as a triangle with Performance, Cruising and Cold Starting being the 3 vertices, and 0.044" gap being the centroid in the middle of the triangle.

You want better cruising...open up the gap, better WOT performance, close it down but doing either will mess with the ease of cold starting. So yes, not optimal, but it's the best setting for all conditions you might want to drive your car in.
 

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Discussion Starter #7
I like that triangle analogy :)

Since I'm not a car person, I do want to make sure we're on the same page regarding concepts:

- Cruising means: ???
- WOT means: the car running at high revs?
- Cold Starting: the needed power to start the car on a cold day?

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09 Altima 3.5SE 6MT Sedan
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Cruising: I meant environmentally responsible driving, light touch on throttle and brakes, typically lower rpms
WOT: meant wide open throttle, pedal to the metal, jackrabbit starts, lots of overtaking, hot engine, crap gas mileage...
Cold Start: conditions experienced with all engine parts cold, A/F O2 sensors offline and still heating, cold plugs, cold oil etc.
 

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09 Altima 3.5SE 6MT Sedan
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and as I think about it...bigger gaps needing more voltage will take more time to develop enough voltage to create the arc...so wider gaps has the effect of retarding your timing, and smaller gaps would advance it...though I have no idea of whether we're talking a few percent or way more.

Retarded timing (aptly named) means the engine is slower to pick up rpms, and too advanced will lead to predetonation (knock).
 

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Discussion Starter #10
Understood... the way I drive would be classified as "Cruising" then. Very rarely do I go above 2000 RPM.

Also, I do believe that your assessment is correct... when I moved from 0.050 to 0.055 I noticed the car taking longer to reach higher RPMs and thus, felt that it'd lost a bit of acceleration. It didn't really bother me as my main goal was to have the engine sound smooth and quiet.

If I found out (somehow) that the only thing I'm losing by using 0.055 is just a bit of acceleration and picking-up in RPMs, while the rest of the ignition system is not being compromised I'd probably leave it the way it is. Otherwise, I'll probably have to scale it back like 0.050-51.

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The difference in .002" mentioned above making the difference in car idle is somewhat ridiculous, at least to me. A difference of that little should make no difference at all. Only big changes like .005"+ will provided the OEM gap was chosen the the middle like all of them are. I routinely set gaps for years at up to .005 smaller to make the tuneups last longer, you set small so the gap wear runs up through the ideal number and it then takes longer to get too big to give issue. I did it on every brand car on the planet and never had any issues at all when I worked garage.

As well, the difference in coil saturation time over say .005" in and of itself will be so little (milliseconds) that the timing has no need to change due to it. The plugs never fire in the exact same place anyway, the moving around on the wire electrode of the jump-to point can have the variance .002" if using a extended tip type plug anyway. And multi-point tips that cannot be gapped are never the same (why I hate them), look at a garbage E3 plug, some of the jump-to points are close to .010" in difference and why they are crap.

Bigger gap is a good thing to work toward but you will stress your ignition parts harder. In my view ANY loss of performance means you are also shortening the life of the plugs, the loss is due to the spark getting weak enough, the mapped fuel then overrides it to begin to slowly foul the plugs and them not burning as clean will then die faster. Less spark has the same effect as too much fuel, if the ECM picks up on it it will lean the motor down to possible damage, unburned fuel being perceived as rich by it. That is potential engine problems. I'd NOT be looking at smoothness ONLY and would drop that gap back down a bit.

Retarded timing also means more heat taken by engine parts unnecessarily. Wider plug gap will lead to better idle but then the car doesn't run as well under load when the ECM goes to WFO full rich fuel, which is harder to ignite.

One way to tell if too much spark before parts start failing is to watch the plugs at the uninsulated portion right under any plug booting. Almost all cars show some slight evidence of spark jumping around the outside insulator porcelain there to get to ground rather than going through the gap as intended. Plugs tend to rust there from the humidity trapped under any covers which are commonly not nearly as waterproof as most think. The quick local heating at a cold weather start then condenses water there to rust and the rust carries spark easily. If that amount of shorting there increases to really show up as carbon streaking then you have too much of something. Once a solid short path is established there then a lot of spark will bleed off to go there and car performance drops off in a miss. I have cured innumerable engine missing issues by simply yanking plugs to then clean that area off really well and same plugs go right back in motor to no miss and they last until the next time years off in the future.

FYI, selling plugs forever proves that not all plugs are set for the exact engine and why they should ALWAYS be checked for gap before going in motor. For one, you have no idea of how many of then get dropped on a hard floor to alter the gap. It's far more than you think. For two, the maker gaps them at only ONE gap and that is the most commonly one used out of all the cars that one plug may go into. Meaning if you don't have the popular gap in your motor the plug gap will automatically be WRONG.

Cruising means low load lean and hard to ignite due to particles too far apart, BUT WOT or WFO (where I come) from means hard to ignite too due to the density, more fuel to have to light off and special problems there as well.
 
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