Spark plug gap for FE on the 1.4T

61760 Views 136 Replies 38 Participants Last post by obermd, Aug 1, 2014

XtremeRevolution

Discussion Starter · Apr 28, 2012 (Edited)

In another thread, I talked with a member named Ian_12 regarding spark plug gap. He informed me that he increased his spark plug gap from .029" to .034". The result for him was a significant improvement in fuel economy.

I have little experience with changing spark plug gap, so I figured someone who had more knowledge and experience on this topic would chime in. On the L67s, supposedly some people reduce spark plug gap to prevent spark blowout under high boost levels, although I'm not even sure if that's actually a problem. My L67 runs on .060 from the factory, and .055 was recommended to me with a smaller pulley and a few supporting modifications, which never really exceeded 14psi total.

I will be trying this tomorrow, but I wanted to know if anyone knew any specific reasons why a certain spark plug gap is chosen over another. .029" does indeed seem to be a bit small.

Reactions: 2

121 - 137 of 137 Posts

wallbngr

· #121 · May 25, 2012

70AARCUDA said:
...this engine (1.4LT) has 9.5:1 (static) CR and the turbo is good for 16 psi stock, so at full boost, the effective CR is closer to 20:1.

...from my earlier posting on this same subject:

I learned something today .. Aluminum engines do have higher compression (aluminum dissapates heat faster) So THAT is how they get 138 horses out of a 1400 cc motor
Ok i understand how that turbo works .. So the 1.4 is comparible to the Ford smallmotor with the Skyactive tech. THat injects exaust gases into the combustion chamber to keep the gas air mixture from detonating ..
The only turbo motors I ever worked on was the old Detroit Desels when I was in the Army 30 years ago ..
These New one are much more sophisticated now

XtremeRevolution

Discussion Starter · #122 · May 25, 2012

wallbngr said:
I learned something today .. Aluminum engines do have higher compression (aluminum dissapates heat faster) So THAT is how they get 138 horses out of a 1400 cc motor
Ok i understand how that turbo works .. So the 1.4 is comparible to the Ford smallmotor with the Skyactive tech. THat injects exaust gases into the combustion chamber to keep the gas air mixture from detonating ..
The only turbo motors I ever worked on was the old Detroit Desels when I was in the Army 30 years ago ..
These New one are much more sophisticated now

I don't think it being aluminum has much to do with the compression. The compression is simply from being able to cram more air into the cylinders when the turbo is creating boost.

The exhaust gas injection has been around for a while (at least back to the early 90s) via the EGR system.

thekevin

· #123 · May 25, 2012

I have fought a lot of egr systems on my vehicles, my 95 s10 blazer with the 4.3 mpi was the worst. I had to pull out the egr motor once a month and clean it.

Being aluminum doesn't have anything to do with the amount of compression, it only allows the motor to handle higher compression because it dissipates heat faster keeping you from ruining parts like the head.

Sent from my SAMSUNG-SGH-I997 using AutoGuide.Com Free App

albow77

· #124 · May 31, 2012 (Edited)

This tank was 42.4 MPG. It was on 87 oct with no eth. I will say that the wind was never in my favor and was working against me most of this tank again. So far I will believe that the plug gap has not changed anything in fuel mileage. Just improved the low end power. I normally ran the 87 oct and got 41 to 43 normally and that has not changed. The one tank that I did run and got 44.7 was with 91 oct no eth and I haven't been able to match that with the 89+ eth or the 87 no eth. I filled up with 87 again and give it one more try before going to 91 full time.

obermd

· #125 · May 31, 2012

albow77 said:
This tank was 42.4 MPG. It was on 87 oct with no eth. I will say that the wind was never in my favor and was working against me most of this tank again. So far I will believe that the plug gap has not changed anything in fuel mileage. Just improved the low end power. I normally ran the 87 oct and got 41 to 43 normally and that has not changed. The one tank that I did run and got 44.7 was with 91 oct no eth and I haven't been able to match that with the 89+ eth or the 87 no eth. I filled up with 87 again and give it one more try before going to 91 full time.

I suspect I'll get slightly better MPG once the car and I adjust to the new low end power. This is because a large part of my commute is borderline between 5th and 6th gears. The extra low end power allows me to be in 6th gear. This will help. The parts of my commute that are fully in 6th gear won't change. I discovered today that I can now shift to 6th at 40 mph vs. 45 mph. This is a 400 RPM difference at 40 mph.

albow77

· #126 · May 31, 2012

obermd said:
I suspect I'll get slightly better MPG once the car and I adjust to the new low end power. This is because a large part of my commute is borderline between 5th and 6th gears. The extra low end power allows me to be in 6th gear. This will help. The parts of my commute that are fully in 6th gear won't change. I discovered today that I can now shift to 6th at 40 mph vs. 45 mph. This is a 400 RPM difference at 40 mph.

The one thing I have noticed is that when the car was bogging before the regap I had a sudden burst of power at about 1700 to 1800 rpm. That burst of power was a shift indicator for me. Now after the regap I have been noticing that I blow right by the 1700 and have been shifting at 2300 to 2500 rpm because it is running better and is gaining rpms a lot faster. Just need to pay more attention!!!!

obermd

· #127 · May 31, 2012

albow77 said:
The one thing I have noticed is that when the car was bogging before the regap I had a sudden burst of power at about 1700 to 1800 rpm. That burst of power was a shift indicator for me. Now after the regap I have been noticing that I blow right by the 1700 and have been shifting at 2300 to 2500 rpm because it is running better and is gaining rpms a lot faster. Just need to pay more attention!!!!

I have also noticed the same change in my car. The transition into full turbo is much smoother than before regapping to 0.035.

DrVette

· #128 · Jun 2, 2012

ECOmaniac said:
Hmmmm...I wasn't talking to you, at you, or about your "educated personal experience", I was speaking generally, should have been more explicit. I can tell you though...you responding to everyone with a condescending/abrasive attitude as if they are digging at you is more of a disincentive to contribute than anything. I am beginning to get a chuckle out of the dissertation length responses you type to a single sentence response and profess all of your statements as if they are gospel. You are always on the defensive..why?

Err, I beg to differ with your assertion of Xtreme Revs.
I think you've judged him wrongly, IMHO his postings have been in good faith not abrasive.
My $0.02 worth

Rusty Wrench
aka DrVette

Reactions: 1

DrVette

· #129 · Jun 2, 2012

wallbngr said:
I learned something today .. Aluminum engines do have higher compression (aluminum dissipates heat faster)

Using an aluminum "head" REQUIRES more compression than a cast iron head to achieve the same power out put due to the heat soaked up by the aluminum.

wallbngr

· #130 · Jun 2, 2012

thekevin said:
I have fought a lot of egr systems on my vehicles, my 95 s10 blazer with the 4.3 mpi was the worst. I had to pull out the egr motor once a month and clean it.

Being aluminum doesn't have anything to do with the amount of compression, it only allows the motor to handle higher compression because it dissipates heat faster keeping you from ruining parts like the head.

Sent from my SAMSUNG-SGH-I997 using AutoGuide.Com Free App

I have a 95 Blazer too and my EGR froze in the -25 weather . it worked again when it warmed up. Those 4.3s get crapppy miliage when you hav to ron in 4 wheel.
I regapped the plugs to .035 and the lowend puwer is MUCH better . Im waiting for the Trans. computer to re learn the shift points .
Before when the trans would shift down at about 25 id shifted hard . Hasn't done that .
Takes a few key cycles to reset it self.
Is there ANY fuel with out ethenol in it around ...
Where I live the low grade gas is 85.5 mid is 87 and plus is 91
The nearest big town I go to shop the lograde is 87 the mid is 89 and The hi 91
I have to do the mid where I live ...
I still am experimenting to see what kind of miliage i get with the premium ,

disco

· #131 · Sep 27, 2013

NGK plug gap bulletin

If you'll notice , the NGK service bulletin to mechanics ; "while using a high-flow air filter , .035 should be the minimum gap as to take advantage of the denser air/fuel mixture ."

obermd

· #132 · Sep 28, 2013

disco said:
If you'll notice , the NGK service bulletin to mechanics ; "while using a high-flow air filter , .035 should be the minimum gap as to take advantage of the denser air/fuel mixture ."

Can you post a link to this?

Sic81

· #133 · Sep 28, 2013

Can you give more details? Is this about our cars or other cars? Which kind of plugs are you referring to, iridium or copper?

6speed

· #134 · Oct 7, 2013

In my plug gap change from .025” factory to .035”, I gained 0.8 MPG & engine accelerates a bit smoother. That was over 20,000 miles ago. A definite no-brainer if someone is thinking about doing it.

disco

· #135 · Aug 1, 2014

I use a K&N with a snorkel delete!
This is a link to the Tech Bulletin!

http://www.ngkplugpro.ca/content/contentfiles/pdf/NGKSP-0606-3-PerformanceAirFilterIssues.pdf

spacedout

· #136 · Aug 1, 2014 (Edited)

disco said:
I use a K&N with a snorkel delete!
This is a link to the Tech Bulletin!

http://www.ngkplugpro.ca/content/contentfiles/pdf/NGKSP-0606-3-PerformanceAirFilterIssues.pdf

No turbocharged engine I have ever seen has a a gap as large as .35 from the factory to avoid possible spark blowout. This is why GM recommends a .28 gap on the cruze 1.4T.

The PDF is interesting but I'm unsure of how accurate the information is as its a bit outdated(from 2006). Modern engines are designed to run E10 fuel with no problems, the computer can compensate for E0-E15 in the cruze with no problem(all 2012+ GM cars can run up to E15 fuel).

Changing the air filter to something with higher flow can confused the computer and cause a lean condition, however if this happens in the cruze it would throw a check engine light. All one needs to make sure is they disconnect the battery so the computer rechecks everything & can adjust for the new found airflow.

obermd

· #137 · Aug 1, 2014

The original gap for the 1.4T engine was 0.033 - 0.037". Anything above 0.037" and you will risk spark blowout at high RPM - been there, done that. The desire to reduce overall maintenance costs/time on the Cruze led to a decision by GM to switch their recommended gap to 0.025 - 0.028" for the 1.4T engine running the OEM/NGK iridium plugs. I measured the gap growth in mine over 30,000+ miles and extrapolated back - starting at 0.029" will result in most of these plugs eroding to 0.035 - 0.037" in 60,000 miles.

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