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Old 08-29-2008, 04:14 PM   #1
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Widening spark plug gap?

I've been thinking about widening my plug gap. I hear that it extends the spark under low load, but doesn't work as well in high RPM. As I rarely run more than 50% throttle this shouldn't be an issue. Stock GM ignition systems generate a good, healthy spark so I think it should power it.

I also read in another thread that widening the plug gap doesn't really work unless you have a wideband o2 sensor. I have no idea if the stock o2 sensors on my truck are wideband or not, and if the cost of upgrading to wideband is worth it.

-Jay
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Old 08-29-2008, 04:25 PM   #2
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Quote:
Originally Posted by Jay2TheRescue View Post
but doesn't work as well in high RPM. As I rarely run more than 50% throttle
RPM != throttle.

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I have no idea if the stock o2 sensors on my truck are wideband or not, and if the cost of upgrading to wideband is worth it.
Count the wires coming off your O2 sensors. IIRC, wideband has 5 wires. Anyway, I'm 99.99% sure that you do not have wideband sensors.

If I understand correctly, it's not a matter of upgrading to wideband, the whole vehicle (especially the computer) has to be designed around wideband O2 sensors.
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Old 08-29-2008, 04:35 PM   #3
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I see. Thanks for your input.

-Jay
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Old 08-29-2008, 04:52 PM   #4
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Widening the gap doesn't usually do anything because it retards ignition timing. If you widen the gap and then change timing you'll get a difference.
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Old 08-30-2008, 09:21 PM   #5
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Considering the fact spark plugs widen as they are used I would have thought this would be something of a non issue.

In other words: As the plugs are used they wear away and thus the gap widens so at some point they are replaced with new plugs with the gaps returned to their starting point.

Pete.
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Old 08-31-2008, 07:41 AM   #6
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Quote:
Originally Posted by Pete View Post
Considering the fact spark plugs widen as they are used I would have thought this would be something of a non issue.

In other words: As the plugs are used they wear away and thus the gap widens so at some point they are replaced with new plugs with the gaps returned to their starting point.

Pete.
I agree.

From my personal experience I have found that I get better engine performance and fuel economy after a new set of plugs properly gapped to mfg specs is installed.
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Old 08-31-2008, 08:47 AM   #7
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My experience from having built and tuned motors with single and dual plugs is that a wider gap DOES improve combustion at low throttle and low rpm. And while widening the gap does induce very minor retard of the spark timing on the order of nano-seconds, the effect is well outside the rhealm of significance for any ignition system with electronic control as it will automatically find the right timing.

The tradeoff to a wider gap however comes at higher throttle. It essentially boils down to whether the ignition system can reliably push a spark through the compressed mixture which is more dense with the higher throttle opening. (Greater mass increases resistance.) The manufacturers set their spark gap specifications based on the expected output of the motor and ignition system. In other words, the exact same motor setup to produce 'x' horsepower efficiently will need a smaller spark gap to produce more power, and can use a larger gap to produce less.

I fully explored this when I had built my 1.6L Isuzu motor to produce close to 400HP. The manufacturers original spark gap specification was for .032", but anything over 220HP or so produced allot of misfires and severly limited output. After dropping the gap to .025", the motor easily produced power throughout the entire range. Doing this degraded idle performance very slightly with a very rare miss occurring, but it was the tradeoff I had to make in the absence of upgrading the spark energy available.

So the question really boils down to how widening the gap affects your acceleration. I say widen it and see what happens. It won't damage your ignition, and probably won't hurt your plugs unless the clearance to the piston is really tight - in which case they will be automatically regapped for you.
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Old 08-31-2008, 11:23 AM   #8
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Thank You Snax. As I rarely push the engine over 2,000 RPM I think a widened gap would be a good experiment. I will wait to do it now though. I just got my new plug wires in today, and my grille block in last night. I'll establish how these mods have effected my economy before I make any other mods.

-Jay
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Old 08-31-2008, 02:03 PM   #9
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Wow...how do you keep it under 2000 rpm? I have plenty of torque to accelerate hard and never exceed 2000 rpm, but my transmission doesn't seem to be aware of that fact, and exceeds 2000 unless even grandma is honking her horn behind me...
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Old 08-31-2008, 02:15 PM   #10
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I can usually give it about 25% throttle and right as it just about hits 2,000 RPM it will shift. You have to remember, my truck has a larger displacement than yours does.

I can probably get away with lower RPM's than you can.

-Jay
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