Spark plug test success! (A-B-A-B = 2% gain with lower heat range plugs)
 

Been having some spark knock since day one using 87 octane under high load at varying rpm ranges. Watched it with scan tool timing advance would get low pulling a hill and would suddenly shoot up when it started to knock. No knock with 89 octane though.

Well I did not want to waste an extra $1-2/ tank on fuel so I found some plugs one heat range colder to test out. Been running these colder plugs for severial thousand miles and mileage seems better. Even hit a 45-46 mpg tank which is my highest ever and seem to be averaging more singe change of plugs. I noticed no more knock on 87 but I was like there is no way it is helping mpg this much and must be in my head or driving style.

So I did an A-B-A-B test today on a 10 mile stretch of road severial times each direction. With oem 6 heat range plug I averaged 52 mpg north and 53.6 mpg south. With 7 heat range plug I averaged 53 mpg north and 54.6 mpg south. This is around a 2% gain from plug change alone!

With colder plug it would hold 2 deg more timing pulling a hill resulting in more power and less downshifts to 5th on some slower inclines which causes real time mpg go down. This was at 50 mph cruise control only. Baro was 98 kpa and 86 deg ambient temp with iats running 107-113 deg. Been averaging over 40 mpg with stock plugs and over 1 mpg more with colder plugs. Been a while since I updated my fuel log though.....

My only question is which of the two vehicles listed was this test done on? Great results

I'm guessing since he was seeing 50+ mpg during the tests that this was in the 2013 Accent, not the minivan.

Thats pretty interesting results. I was looking into why this would happen/make a difference in mpg. I came across an interesting thought that the ethanol in our fuel was causing a need for lower temp spark plugs to prevent detination. I don't know if that is the cause but I am interested in maybe trying this out at some point. I can only find E10 gas here.

Im curious at what point the increases fall off if you went another step colder?

I opted for 2 steps colder ngk's on my car but didnt do any real testing to have data to back up my fuel economy but was able to advance my distributor almost all the way...

Did the plugs you removed show any signs the heat range needed to be changed?

Isn't that backwards?
 

I thought the presence of ethanol increased the octane, not lowered it. I understand you can jack the compression on an engine that only ever runs E85 up to crazy high levels with no risk of detonation. I don't know what the ignition thresholds are like for ethanol but I reckon if it's harder to ping, it's probably a little harder to light, too. I'm just taking a flyer here, but I would think ethanol would benefit from a hotter plug, not colder.

OP is taking advantage of his computer's programming to maximize economy with a colder plug, which permits more advance and therefore a more complete burn.

Correct...the van falls behind the accent by ~20 mpg.....

You can only go so far with a plug change as it is only one area that can have too much heat and cause knock. Lowering thermostat temp may help you get a few more degrees of timing out of it by making cylinder walls cooler... Each setup is different so test away!

As in what kind of signs? Color looked good imo. Not wet/dry fouling noted. Ceramic body of plugs from hex head to maybe 1/4" toward top of plug was turning a burnt rusty brown color though. Coil side of hex not threaded end... Not sure if this is normal or sign of too much heat? Around 30k on oem ngk iridium plugs...

Running e85 allows you to run more power ie timing, compression, boost, ect. You can run a hotter plug with it but if you want to take advantage of it run a colder plug and adjust timing, compression, boost near knock threshold fore more complete burn.

Correct...I am trying to take advantage of the oem tune with 87 octane. With this somewhat high compression(11:1) engine it is easier for knock to be triggered. Also seems the tune is on the edge for best fuel economy in areas which was having slight knock. Seemed like any area high load where computer did not richen fuel up it would start ticking and knocking. I do not think going colder than this will help as I should not be losing any power through knock at this point and taking advantage of oem tune and 87 octane. Now if I can change to colder thermostat or fool ecu with resistors on coolant temps, iats, ect it may make it adjust more timing with no knock. However it will also adjust afrs, fuel pressure, cams open/close, ect. The tech in this little engine scares me right now so I am taking it slow and learning how it works and responds to things daily via scan tool live data before planning next mod...

Computer on this thing is strange. Hard as heck to go open loop. Have to be in gear down a pretty steep grade for several seconds and if using cruise control seems to want you at least 3-5mph over set speed before it will go open loop dfco. And at wot open loop will only happen in very high rpms and sometimes not in lower gears. It will however stay closed loop and richen mixture slightly at same time which is why I say it is weird. Afrs go to mid 11's during wot open loop.

I would also like to add that dealer told me that it was not knock but sound of gdi engine and high fuel injection pressure. They are right about high fip as it idles around 60psi and goes to max of around 2200psi under high load. They were wrong about it not being knock as the sound is gone and pretty much everything except for timing in certain areas changed.

The discoloration of ceramic body sounds normal. Were you want to look is the business end.

Third image down:

NGK Spark Plugs USA

Also more info here:

NGK Spark Plugs USA

The business end on the oem plugs looks good from what I can tell. I can not tell much of a difference between oem and 1 step colder. I wonder if the the knock was so little that it would not easily show up on the plugs but was enough to see a gain from going a step colder on the plug. I may run this same test in the winter to see if I get same or similar results with colder plugs.

Good to know. I wonder what similaries our engines share considering they are both Hyundai products. I'm still curious if this would work for my elantra. I'm not having "knock" issues so I'm inclinded to say it may not have the same beneficial effect.

You are hitting on the entire purpose of having a full length insulator.

This weekend, I pulled the original plugs from my wife's 2007 Honda Fit, and the insulators had a very light brown color to them, which is perfect.

Back in the 1970's, motorcycle ignitions were notoriously weak in voltage, so if the ceramic insulator was too short (i.e. cold), and you happened to ride a two-stroke, the insulator would get a thin film of oil baked on it, then that cylinder would stop firing all-together.

Why?

Because the insulator is *supposed* to run hot enough to keep cylinder deposits from building up on the insulator, and keep it from conducting the voltage from the tip, down the ceramic to the metal casing.

To make the most of the available spark energy in the ignition system, I would want the insulator to be the highest resistance (to ground) item inside the cylinder, and keep it that way.

With a strong spark, most of the available fuel will be more fully burnt, and thus give better fuel economy.

Placing a plug with a shorter insulator only compromises the spark system, and increases the chances that the spark will leak off some of it's potential voltage before jumping the gap across to the electrode, because when it's colder, it can not burn off the carbon deposits more readily.

The objective is to keep the insulator hot enough to keep it clean, but not to the point of over-heating.

Cycle magazine had some excellent articles from the 1970's, on how to read spark plugs. These would go a long way in helping to the get the proper spark plug range for each running engine with it's specific requirements.

Jim.

i've got a question do you have a multi-meter; if yes do a continuity test(or resistance test) on the hotter plugs between the electrode and the metal body.

Not sure. I have the 1.6 gdi engine in mine and it is 11:1 cr. Yours has the 2.0 right? Not sure of the cr on it though or if you have any knock. I only have slight knock/ticking using oem plugs with 87 octane, high map pressures, high load, and at varying rpm. Sometimes you have to know what to listen for and sometimes it is obvious.

Tried this when I first got the new plugs but for some reason multimeter could not read it. Number would not read or jumped around a bit. Maybe it needs new batteries? I will try again though. What would this mean if there were a difference?

At first thought, this *should* work. Use a multimeter to apply a small voltage to the insulator, and measure the resistance of the insulator to ground.

*However*, this approach is not valid as the voltage level goes from let's the 0.5 volts that the meter puts out to measure resistance, to the 30,000 volts that the ignition system applies to the spark plug.

The effective resistance values of these two measurement methods will give completely different results.

Some multimeters provide "ranges" for different applied voltages to the test item, and these in turn give different effective ohms readings as well.

One would need specialty equipment to measure the effective resistance of the spark plug at operating voltages.

And then let's not forget, that as the insulator heats up, the resistance will change again.

_____________

Even if one had the proper equipment to do the above, it still does not define the intent of spark plug heat range on a running engine.

The intent of the insulator length is to simply keep the insulator running at a temperature that allows it to stay reasonably clean from contaminants, and thus provide a solid spark to the cylinder.

If the ceramic gets too hot, the shiny surface finish changes to a grainy, lower resistance surface finish, that then allows more contaminants to adhere to the finish, resulting in spark loss to ground.

Too short of an insulator, allows the ceramic to build up more deposits, and again, allows spark to short to ground.

The heat range is carefully selected for the reasons above.

Jim.

if you set it to megaohms it'll tell you if you have an easier path to ground, then the electrode tip to the spark gap; which would indicate if the spark plugs were needed to be changed anyway; considering any megaohm reading is bad if it's suppost to be insulated.

v=i*r

So what is the current (no pun intended) state of this discussion? Colder plugs might be better for FE but harmful to the engine? I am interested in this but still a little confused.

Colder or hotter depending on the situation may or may not improve your mileage.
From the NGK website:

In nubbzcummins case.
The long term effect of running this plug has not been determined, being colder it may not fully burn off deposits and require more frequent replacement or a cause long term reduction in fuel economy. The most common reason for changing heat ranges is engine modifications an example: raising the compression. A car that is burning oil might benefit from hotter plug to reduce fouling.


Go here for a spark plug overview:
NGK Spark Plugs USA

Very interesting thread. I am curious because the wife's 08 Avenger will knock on 87 octane; I've been running 89 for a couple years now to avoid that. It's a 2.4L that runs 10.5 CR. Never thought of running a range colder plug.