# Spark plug gap???



## chevycruze2012 (Nov 13, 2012)

70AARCUDA said:


> • OEM (stock) is _supposed_ to be 0.027"
> 
> • "TUNED" recommendation is 0.028"
> 
> • DIY MPG'ers uses 0.032"(typical)-to-0.035"(extreme)


So I would see better results if I gapped them to 0.35" if I'm going for performance and mpg?

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## brian v (Dec 25, 2011)

70AARCUDA said:


> • OEM (stock) is _supposed_ to be 0.027"
> 
> • "TUNED" recommendation is 0.028"
> 
> • DIY MPG'ers uses 0.032"(typical)-to-0.035"(extreme)


These are the correct plug Gap allowances , It is your choice to make for the desired affect that you seek .


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## chevycruze2012 (Nov 13, 2012)

brian v said:


> These are the correct plug Gap allowances , It is your choice to make for the desired affect that you seek .


Okay. Sweet. Ill try it at 0.035" and see what that does for me...and hopefully it gets me where I want lol

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## obermd (Mar 3, 2012)

The original 1.4T spec in GM Global connect was 0.033" - 0.037"


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## chevycruze2012 (Nov 13, 2012)

obermd said:


> The original 1.4T spec in GM Global connect was 0.033" - 0.037"


Okay cool. Thanks man. Now I just need to track down my spark plug gap tools haha.

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## NickD (Dec 10, 2011)

If bigger is better, try a 60 mil gap like the original HEI's used, they you really would get a lot of misfires if that is your goal. And increasing the number of misfires increases the odd of breaking down both the coils and ignition driver circuitry. If that plug doesn't fire each time, they have to eat up that energy.


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## chevycruze2012 (Nov 13, 2012)

Yeah...I just bought a good one from lisle of the coin style. Like this one.
View attachment 34417


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## brian v (Dec 25, 2011)

You'll learn the hard way . 
We suggest a pair of plyers to adjust the ground electrode only , feeler Guages for measurements .


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## justjohnthomas (Jul 27, 2013)

There is an entire (long thread) on here with members perceptions and opinions on this topic. Search (or just a quick look http://www.cruzetalk.com/forum/showthread.php?t=6722 ) would answer this question without creating new topics to hinder further searches.

On another note, disk are the worst way to go. Quality feeler gauges are your friend. Rember it doesn't take much movement on the ground strap to drastically change gap...just dont get frustrated and throw it at your garage wall. If you get too far out of spec you'll know when you drive it


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## obermd (Mar 3, 2012)

http://www.cruzetalk.com/forum/57-how-library/6722-diy-re-gap-factory-spark-plugs.html includes all the tools and a video from NGK on how to regap your spark plugs.


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## Sunline Fan (Jul 29, 2012)

Quite frankly I'm shocked that someone with nearly 1000 posts around here doesn't know the suggested spark plug gaps by heart. It's not like we don't ever suggest or discuss them around here.


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## chevycruze2012 (Nov 13, 2012)

I know what the manufactures recommended plug gap is since ive read the owners manual twice.....I was wanting to know what the best gap is for optimum performance and mpg ratings. That's all lol


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## brian v (Dec 25, 2011)

Sunline Fan said:


> Quite frankly I'm shocked that someone with nearly 1000 posts around here doesn't know the suggested spark plug gaps by heart. It's not like we don't ever suggest or discuss them around here.






Yeah ! I'm thinking he is looking for some thing new to clean ..
We will have to get him involved in the Baseball league then the Bowling league then the cleaning league , owe wait I want to park me cruzen in his garage for a day .
Besides learning a few things about useless tools which never get mentioned in these under read how too 's .


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## NickD (Dec 10, 2011)

Semiconductor components have a key specification, breakdown voltage, and the greater the breakdown voltage, the greater the $$$$$.

Have a hunch the reason reason why Chevy reduced the spark plug gap from 35 down to 28 mils was to comply with the lower breakdown voltage of the components they are using. 

Breakdown voltage should be a self explanatory word, if the voltage exceeds the breakdown voltage, those components will break......down.

Not only the electronics, but the coil itself has a breakdown specification, and if just one coil breakdowns, have to replace all four.

And the larger the gap, the greater that voltage.


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## Patman (May 7, 2011)

I reset my plugs to .035 in my Eco and I noticed a loss of power(weak spark). When put back to stock(.028), the power was restored. I did that last night and still on the fence for MPG but the car does run much smoother now. FWIW, I may try .032 but .035 felt like it caused a weak spark. I have 2 sets of plugs. The set in the car now are the stock NGKs, the set I took out were replacement AC Delcos I bought not long ago and set to .035. This topic has been "dragged thru the mud". I think the biggest discussion that came out of it was the inconsistency of plug gap. It all turns into personal perception, despite what the actual MPG is, if you are not satisfied with how the car runs what is the difference. I am staying with .028 for a while. I asked one of the hypermilers here what mods he had and he said he was stock so I am presuming somewhere @ .028. But he lives in Idaho and has 100000+ miles on his car already(2012 Eco).


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## Vetterin (Mar 27, 2011)

+1 Patman! I have run my plugs at .030, 032, .035 with little noticable difference. Last weekend I replaced my plugs with the cheapie Autolite coppers set to .028 and the car still feels the same so .028 is where I will stay........for now....


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## NickD (Dec 10, 2011)

Power versus fuel economy is completely opposite in the fuel system, the richer the mixture, the more the power and less fuel economy. Whereas the leaner the mixture, the better the fuel economy, poorer the power.

Ignition is just the opposite Peak power and fuel economy occur at the same exact point. In theory, can't improve the performance of the ignition system if you get a hot spark at the right time. With power, far more combustion chamber turbulence that is likely to blow out a weak spark. But not nearly as noticeable when driving at a constant speed.

Never hurts to have a good hot spark. Actually the older ignition point systems gave a much hotter spark than these transistor types. A transistor hasn't been designed yet that can be switched off a fast as a set of opening points. Its that rate of change that induces a much higher voltage than a relatively slower transistor. But the reason for the change is reliability.

One of the best solid state ignition systems ever designed is the capacitor discharge system. A 1-2ufd capacitor is charged to 400 V, and an SCR dumps that charge into the primary of the coil. But this requires a most costly 12 to 400 V converter. With these current designs, just get barely enough circuitry to replace the points.

With the capacitance discharge system, the energy storage of the capacitor can be chosen to match the energy consumption of the coil, so you end up with a flat voltage output across the entire speed range of the engine. But in the barely point replacement type circuits, the dwell time decreases with engine speed. So end up getting a weaker spark when you need it the most. Only choice is to decrease the spark plug gap.

Try to sell capacitive discharge systems to the bean counters. I gapped my Cruze at 25 mils and enjoying both power and economy. Actually very large compared to my two cycle single cylinder engines, chain saw runs at a consistent 6,000 rpm. There the spark plug gap is 15 mils. Any larger and it won't start or run at all.


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## babymobilcruze (Aug 17, 2012)

You sure richer mixture more power? Especially in turbo motors that come super rich from the factory, a tune that leans it out adds power. Hence the need got an a/f gauge to ensure its not too lean and go boom. Ever heard the saying "it was never faster until right before it blew up"


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## NickD (Dec 10, 2011)

Think so, what do you think. 

Cruising down the highway at a steady speed, TPS remains constant, reasonably, PCM is in close loop, O2 sensor maintains the AF ratio at a near perfect stoichiometric ratio of 14.7:1. Turbo is in idle position. Spark advance is close to the anti-knock position for maximum fuel economy. Help to use the highest octane.

When you hit the gas, TPS tells the PCM to get out of close loop mode that enriches the AF ratio to approximately 12:1, not precisely sure what the Cruze is using, but this is a long standing power ratio. PCM is in open loop mode at this time, enrichment is gained by increasing the dwell time of the fuel injectors. Turbo kicks in, manifold vacuum drops even going positive that decreases the spark advance as it takes longer to burn that extra fuel.

Feel a bit of torque on your butt, instantaneous mpg drops to near nothing and instead of idling along at about 20 HP, that little 1.4L is kicking butt close to 138 HP. This is when you need that enriched fuel mixture.

Do this frequently and your stops to the gas station will go up exponentially. PT wear also increases exponentially with increased power demands.


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## 70AARCUDA (Nov 14, 2010)

For G100 gasoline, best "*power*" comes at about *12:1* AF-ratio while best "*economy*" comes at about *16-18:1* AF-ratio. E10 is pretty close to these values as well but E85 is NOT!

Smog crap regulations limits "acceptable" (per EPA & CARB, et.al.) to "*stoichiometric*" *14.7:1* AF-ratio because of catalytic convertor operation.

The only time the ECM permits "rich" running is for (a) cooling (ie: turbo-boost) and/or (b) WOT (ie: power). Otherwise, the ECM tries to keep engine in "closed-loop" operation at 14.7:1 AF-ratio as much as possible.


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## NickD (Dec 10, 2011)

Bit of buck passing going around with this technology, going back to the Model A Ford, it could burn just about anything. But as faster cars were in demand, compression ratios were increased, A was about 5:1, detonation occurred and combustion chamber temperatures drastically increased forming oxides of nitrogen.

Cure back then was to add lead to gas, but very little was known about the brain deformation particularly to children, adults became for more aggressive. Solution was to phase out the lead. But back up to high combustion chamber temperatures again so valves would burn out and even holes would burn through in aluminum pistons. Some unsuccessful attempts were tried to make engines out of ceramic. But still would not cure the NOx problem responsible for developing lung problems with people. 

Outside of not using lead for cooler combustion chambers, oil companies couldn't come up with a different safe substitute. Least this is the story I heard, so the buck was passed to automotive to attempt to solve this problem. WW II aircraft did not use lead, but used unleaded gas with water injection to cool things down. This led to the EGR valve development where up to 30% of the exhaust is recirculated back into the engine, with a defective EGR valve, your engine will burn up. And in effect your 100 CID engine is only a 70 CID engine.

A better method is to close the exhaust valve early to keep some of those exhaust gases in a cylinder. Typically EGR is only needed at engine speeds above about 1,500 rpm that completely contradicts our current low displacement high revving engines.

After all this horse trading, still need that stoichiometric mixture for combustion chamber temperatures. Lean burn engines can't do this, the heat absorbed by the gasoline to change its state from a liquid to a gas is enormous, cut the gasoline, the heat goes up, as does the NOx production.

Solution is yet another after the fact to undo the damage caused inside of the engine with a three rather than a two way catalytic converter. Latest technology is to add barium to the cat, but acts more like a storage device. And when it gets saturated with NOx, only way to clean that up is to decrease the AF ratio to the power level. The excess HC's are burnt in the cat, not the engine, so the cat would get extra hot to clean up that barium. So whatever is gained in economy is wasted in clean up.

Major fault with the cat, positively worthless unless its red hot, and will never get that way making two block trips in your car to the local bar or whatever. Was talk about electrically heating it first that came up in around the mid-80's. But showing energy losses in doing this to the EPA, economy would be drastically affected. We showed where we could improve the efficiency by a factor of around six by spraying gas directly into the cat, but the DOT was not too hot on this idea.

Yet another not very advertised problem with the car kept quiet is importing oil in particular from the middle east that has a high content of sulfur in it. With the high temperatures in the cat, HC's, and O2 and with the S, H2SO4 is the output burning holes in our lungs, sulfuric acid. 

You guys talk about tune with no idea the problems the automotive industry is facing, lead, sulfuric acid, and carbon monoxide are killers to human beings. Let's not even get into MTBE's.


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## 70AARCUDA (Nov 14, 2010)

NickD said:


> ...WW II aircraft did not use lead, but used unleaded gas with water injection to cool things down.


Uh, sorry, but your WWII history is flawed -- ALL wartime fighter/bomber piston engines used 2-to-5 times normal amounts of lead (tetra-ethyl lead: C_8_H_20_Pb) for KNOCK control (purple AVGAS 115/145), not cooling. Water-methanol injection was used for "short bursts" of combat cooling. And, very low/unleaded gasoline was pretty much reserved for use in rationed home-land vehicles. To my knowledge, NO combat aircarft used no-lead fuel.

The Wright R-3350 turbo-compound radial engines on our USN Lockheed EC-121 "Warning Star" radar planes required AVGAS115/145.


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## NickD (Dec 10, 2011)

Do appreciate being corrected if I post an error, just recall reading this in a late 60's issue of SAE Engineering in preparation for unleaded fuels with the new challenges involved.

Do have to agree with the heavy use of lead in WWII aircraft, lead spark plug fouling was a major issue. This site points this out. http://www.wwiiaircraftperformance.org/150grade/atsce-28march45.pdf 

Tried using ethylene bromide in fuels to keep the plugs clean, worked, but caused other engine corrosive problems. was easier just to replace the plugs as low as every 15 hours.

Ha, if I still had that old issue of SAE, would write for a correction to that statement.


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## 70AARCUDA (Nov 14, 2010)

It sounds to me like that SAE article was referring to the commercial and private aircraft use of gasoline, as they WERE cutting back on lead in the late 1950's (post Korean War) and early 1960's, because most commercial planes by then had moved from reciprocating engines using gasoline to jets or prop-jets burning JP-fuels. That left the private pilots to use low-lead (100LL) in late 1960's early 1970's, which lasted almost up to Y2K, when un-leaded was introduced. I believe leaded aircraft fuel is rather scarce (and expensive) these days.

Current aviation gasolines & lead content (mL/gal):

Unleaded......82UL octane; 0.0 mL/gal.(*purple*), phased-out in 2008!
Low-lead.....100LL octane; 1.2-2.0 mL/gal.(*blue*)
Leaded.....100/130 octane; 3.0-4.0 ml/gal.(*green*)
Mil-AVGAS..115/145 octane; 4.6 mL/gal.(*purple*), discontinued, only made for special/racing events.


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## NickD (Dec 10, 2011)

70AARCUDA said:


> It sounds to me like that SAE article was referring to the commercial and private aircraft use of gasoline, as they WERE cutting back on lead in the late 1950's (post Korean War) and early 1960's, because most commercial planes by then had moved from reciprocal engines using gasoline to jets or prop-jets burning JP-fuels. That left the private pilots to use low-lead (100LL) in late 1960's early 1970's, which lasted almost up to Y2K, when un-leaded was introduced. I believe leaded aircraft fuel is rather scarce (and expensive) these days.
> 
> Current aviation gasolines & lead content (mL/gal):
> 
> ...


Sounds like both of us have been around the block a couple of times. But that article was referring to using water injection. Now trying to think of private planes that employed water injection in lieu of the EGR.

Were very simple when they came in in 72, venturi vacuum went to a vacuum thermal switch directly to the EGR valve, only active when the engine was warm. Guys soon figured by blocking that vacuum line, would get all kinds of HP. But not for long, needed a valve job. EPA said only for NOx reduction, nothing about burning up your engine. Many found that out the expensive way.


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