Has anyone done spark plug gap tests?
 

I've done some searching and see most people try to dabble in iridiums or other "upgrade" plugs. I've personally always stuck with plain old coppers; they've always worked best. It also helps I've got a simple 8v i4, so spark plugs are a quick 5 minute job.

For the 80's vw's, gap spec is 0.028 +/- 0.004. California spec is 0.028 + 0.004.

For pretty much as long as I've been changing out plugs, I've gone with bosch coppers, and kept the 0.032 gap, since in theory, that should be best?

But on a current car that I've been tuning up (1990 vw fox, ke-jetronic), I've killed off all vacuum leaks; pulling almost 20 inches at idle. Full ignition tuneup. MSD Blaster 2.

Before the tuneup, car had some old bosch platinums. I'm not sure of the gap. Don't have a tool at the moment.

But after swapping in the coppers, the idle is noticeably lumpier. Still trying to fix a lean running problem as well, so I'm not putting it specifically on the spark plugs (failed smog two times in a row now. insane NOx, but that's another story, not related to this topic..)


So taking this application as an example, has anyone tried say 0.024, 0.028, 0.032, 0.035, 0.040, 0.044?

I had a 1991 vw fox; pretty much the same car, albeit with digifant management. I've also used bosch coppers on that one, and after 20k miles or so, when I goto change the plugs, I'll often find the plugs have worn down / been blown out to 0.035-0.044 easily.

What's the response to different gapping? I haven't checked to see what color spark I get, but I can't imagine it being anything short of blue, since coil, wires, cap, rotor, and plugs are all new, and I added an additional ground strap to the valve cover.

I don't know, I tried Bosche +2 platinums in my Jeep, but it seems that they don't like them. I'm gonna get new copper plugs soon and see if it helps my really rough Idle situation. I hope it does.

I'm guessing that you should use whatever type of plug your vehicle was designed for, (unless you have an aftermarket ignition system) because voltage sent to the plug might create a stronger/weaker spark because of the metals used have different conductions of electricity. The escort used platinum plugs, so I used those, and it worked out great, now I'm gonna switch back to copper on my Jeep and see if that works out great.

Never messed with gaps though. I go with the assumption that whatever the spec is that the manufacture made is what is best for the most reliable, best burn possible without misfire, or weak spark, as well as long plug life. Wide gaps have to be regapped more often.

If your new Blaster 2 has runs at a higher voltage than what you were running before, you should be able to take advantage of by using a larger plug gap. If this is the case you may see increased erosion on the plugs & may want to consider a different electrode material. If it runs at the same voltage you will probably need to use a similar gap as before.

I swapped in a GM HEI distributor into my Jeep. From 30,000 to 40,000 volts. Stock .035", now .042". I can notice a difference. But there are other differances between the two distributors also.

Don

I don't mess with gaps either when upgrading. It seems funny to read 40000 volts, I upgraded an old sube from <7000 to 11000.
In 2007, I swapped out the three remaining original NGK old school "crap keepers" after 20years (exactly the month it turned 20- Freakin amazing). the bosch platinums work nice on the lower coil at 11000.
I too run an 8v 4cyl engine, but its a boxer. Different world of physics for the fires. Inlines need special attention, as most long time users figure out. I would go with the coppers too if in the scenario, and wouldn't even step up the coil too far unless the head was known to be a bullet proof rock, as well as pistons. most 8v are anyway, but there is extremes there too from the past.(ie, 83 escort)

I'm going to try gapping my plugs down to 0.025 soon. Definitely am getting god mileage right now though. I've got a real heavy foot, so take that into consideration. I need to source something cheap to replace my leaking filler neck hose. OEM part is $80 for 5" of rubber. No thanks.

Right now, the plugs are 0.032, and the idle is a bit lumpy. Back with 0.028 platinums and an aging stock coil, it was smooth as silk.

But on the last tank, I lost over 3 gallons due to the leak, and still managed 25mpg. That'd have been almost 36mpg if it weren't for the leak. Includes a lot of lead foot and maybe 50/50. Too bad the good mileage is also from running excessively lean. Somehow, the o2 ecu is still thinking everything is normal, even with a new o2 sensor. I'm pretty sure the noisy fuel pump isn't putting enough fuel pressure for the system. NOx was almost 3x the legal limit for the car, and about 9x higher than "normal"

It's so bad the back bumper by the tail is browned from heat, vs black from rich or nothing with neutral.



Come on, someone has to have tried different gaps. How does heat range come into play as well? Wider gap and higher heat range? Or lower? I'm not looking to lose any performance. If anything, gain performance, especially now since I want to be able to fully utilize the msd blaster 2. Hell, performance and economy should go hand in hand, discounting driving habits.

Mods that result in increased engine efficiency give you more horsepower OR better fuel economy: you choose with your right foot. Better driving habits are more effective than any mod.

When it was time for new plugs, I took a few measurements. My fuel consumption at idle and at 3000 rpm in neutral was unchanged when I swapped out the Autolite copper plugs with 40kmi on them for Denso copper plugs.

Denso came out with the Denso Platinium TT, and their ads boast about a 0.54% improvement in fuel economy, from 36.8 to 37.0mpg, versus "Competitor A". They don't say under what conditions, so you can't draw any conclusion other than that Plug A vs Plug B isn't going to make more than a 0.54% difference in power or economy. Utterly invisible to your butt-o-meter, and almost certain to be drowned out by noise in the data at the pump.

The manufacturer of your engine spent hundreds of engineering hours (I hope) optimizing the ignition system. If you believe it was optimized for performance/economy instead of cost, then I wouldn't mess with it.

The best place to test different gaps and different plugs is a bench dyno, but since I don't have one of those in my garage either, I'd be happy to read any data you collect on the road or in the driveway.

Everyone is talking about modifying the plug gaps across all cylinders in the engine, but has anyone tried using different plug gaps for different cylinders? It sounds crazy, but I was reading an article on Autospeed about cylinder-specific tuning, and the variance in AF ratios and other factors for different cylinders in the engine was reasonably large.

The Autospeed article
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For instance, one of the situations in which cylinder imbalance of Air/Fuel ratios would occur happens when an assymetrical intake is utilized:
http://www.autospeed.com/cms/gallery...0&a=109725&i=5
In this situation, the air is taken in through one side of the manifold, before being distributed through the various, equal length runners to the engine. From the flow diagram, it seems that the runner farthest from the intake port would be receiving the most air, while the runner closest to the port would be receiving the least.

Now, because the engine is running in closed loop (feedback from the O2 sensor and various other engine points determines fuel delivery), the amount of air reaching each cylinder plays a major role in determining whether the car runs as close to 14.7 to 1 as possible. Due to the fact that many cars run a single O2 sensor, that sensor is only seeing the average of AF ratios from the engine. Also, each cylinder recieves the same amount of fuel (because there is only one O2 sensor, fuel isn't automatically adjusted for each cylinder). This would mean that some cylinders are receiving more fuel than necessary, and others less than they need.

For instance, the cylinder farthest from the intake (I'll call it cylinder 1) is receiving much more air than the other cylinders, while also getting the same amount of fuel. This would cause it to run leaner than the other cylinders. The opposite cylinder, closest to the intake is receiving less air with the same amount of fuel, causing a rich condition in that cylinder. To protect the engine, most cars will err on the side of delivering too much fuel, rather than too little. This means, if the O2 sensor finds that the average cylinder AF ratio is too lean, it will immediately enrich the mixture, thus impacting fuel economy. While this will average out to approx. 14.7-to-1, the cylinder that is running lean is also influencing the knock sensor of the engine. Engine knock, or detonation is primarily seen when an engine is running too lean for the operating conditions. When knock is detected in fuel injected cars, the vehicle's ECU immediately responds by retarding the ignition timing (less power) and dumping more fuel into the engine to eliminate the lean condition.

So basically, cylinder imbalance can result in the car using more fuel than necessary to compensate for the differences across the cylinders.

What I'm wondering is whether it would make sense to counter this with variable plug gaps across a given engine. My 96 Accord uses an intake setup similar to the flow diagram pictured, so I figured that by using a narrower plug gap at the same position as cylinder 1, and a wider gap at cylinder 4 (in my case, the cylinder closest to the intake), the cylinder that is running rich would burn more fuel, while the cylinder running lean would burn less.

You might have something here?

I haven't tried different plug gaps to control lean/rich conditions, but I do use my management system to control individual cylinder fuel and timing trims.

This makes a big difference and you would be surprised how much there is to gain.:thumbup:

pgfpro,

How do you tune individual cylinders? How do you get your feedback for individual cylinders? I guess you do this on your del sol.

On TDI engines, each power stroke is sensed by the crank sensor and fuel trims for individual injectors are adjusted to compensate for variations between cylinders and injector bodies and make the engine run smoother.

On a gas engine with perfectly matched injectors and cylinders I can see how you could compute individual cylinders AF ratio from the power they generate given an equal quantity of fuel injected in each cylinder. But as soon as there are mechanical variations between cylinders, say uneven compression for example, or something that throws an injector's flow off, that all goes out the window.

I think it would be easiest for manufacturers to ensure their intake manifolds evenly distribute air between cylinders, or just go with an o2 sensor per cylinder.

I'm going to go ahead and try it on my Accord. Don't know if I'll be able to do any A-B-A tests today, since everyone is going to be out christmas eve.
I'm planning to set the plugs as follows: (MFG recommended plug gap .039 to .043)
Cylinder 1 (farthest from intake): .035
Cylinder 2: .039
Cylinder 3: .043
Cylinder 4 (closest to intake): .045

Don't forget to index them.

Yes I'm running it through my engine management. What I found is when it goes into lean burn mode the cylinders change a lot between each other.
I'm still not to sure why but I have some theory's. So what I do is run the car on a chassis dyno and run four individual W/B O2 sensors.

The SAE (society of automotive engineers) already answered alot of these questions it seems, I checked that paper out at my libarey a few years back, so not all the info is fresh in my mind, but from what I remember serfice gap plugs like Botsh +2 and +4 platum plugs have a cooler spark due to the spark travling accrose the ceramic insulater, they also worked better with some styles of engine combustion chamber over other styles, I think larger might have been better, it sticks in my minds that big amarican V8's worked best with this style of plug, I could be wrong on this however.
With standard style of spark plugs that most people are used to the smaller the gap the hotter the spark, the draw back to this smaller gap was that less fuel/air was in the gap so the flame spred was slightly slower if the gap was to small, with to large of a gap the spark was cooler and did not ignite the fuel/air as well, higher voltage helps to a point but to high and it caused other problems in other parts of the igition system.

A larger gap should help with FE as you should get a better burn. The problem with large gaps is it takes more voltage to fire the plug. This starts to become more of a problem as rpm and load increase. Also as a plug gets dirty, its easier for the path to find a short to ground as the larger gap must be overcome.

The energy for the spark is stored in the ignition coil.

As I understand it, the spark lasts longer if the gap is smaller. And if the gap is enlarged the voltage between the gap gets higher before the spark jumps and the spark duration is shorter.
I think the spark energy is the same in both cases.

Once I verified this with a scopemeter. I had different gaps in different cylinders and I could see that the gap affected to spark burn time.

I'd also like to know what affect it has to FE

So, I tried it out, and it seems like I gained 2 or 3 miles per gallon on the highway in my Accord. I haven't A-B-A tested it yet, but running at between 65 and 68 MPH on the highway left me with 33 MPG (I-95 from Georgia to Maryland). No other mods except an upper grill block and Scangauge. Generally, I make the drive with rear wheel skirts and a lower grill block and get 34 MPG (driving at 60-63 MPH). Acceleration also seems smoother, but I want to pull the plugs and do some kind of official testing first.

A couple of years ago, my SE-R's mileage started going down on long Summer highway trips. Mileage dropped from 38 mpg to 36, same drive, same Summer. Since I hadn't changed anything else, I replaced the plugs. Their gaps were all in the .055 range. After I got the new plugs in, my mileage went back up to 38 mpg on long highway drives.

...look up SAE paper #700081:

Spark Plug Design Factors and Their Effect on Engine Performance,
by: Robert J. Craver, Richard S. Podiak and Reginald D. Miller,
of: Champion Spark Plug Co.

I was wondering if anyone had done tests on this, then decided to do my own. I have a 4 banger, so changing gaps across the board is not time intensive at all.

I changed the gaps, and then checked the vacuum. Then I changed the gaps, and checked the vacuum again. Here's the data:

No, my gauge doesn't have decimals, but the needle moved so little between tests that I figured I should use decimals.

My question is how this relates to FE. Does higher vacuum mean higher efficiency?

holy smokes, 0.060! What ignition coil are you using? I've never went further than 0.040. Currently on 0.028 (spec). I've got a msd blaster2. Maybe I'll try 0.060 next time.

Cheers

This is apples vs. coconuts, but may have some relevance:

1. In BMW oilhead boxer horizontal twin 4 valve/cylinder motorcycle engines, surging is a big problem, so various sparkplugs and gaps have been tested. 4 prong and platinum or iridium plugs make the problem worse, impede the flame front, and degrade fuel economy and power. Best power, fuel economy, and surging relief are with plain old cheapo single prong Autolites set at 0.038 or as wide as possible as long as she runs well.

2. Aircraft Spruce & Specialty Company sell inexpensive cylinder head temperature sensors, actually little rings that fit between sparkplug and head with a wire to the readout gauge. Maybe such should be used in conjunction with testing various spark plugs and gaps among the cylinders.

Nice. I've always stuck with traditional copper plugs. #2 is a very interesting idea indeed. I'll do some testing later this summer, but I have a feeling I'll be stuck with narrow gaps since I'm going forced induction.

For now, I pulled a plug today (installed last year around this time @ 0.028. got 10k miles on them) and measured it to be 0.032. Not bad. At this rate, I can imagine these cheapo coppers lasting at least 30k miles.

from platinums to a classic style.. advance the timing a few degrees...and retard. See what works.

I went through this on a rock chunk steel 1950s style NGK plug in a 1987 subaru. the platinums fired so fast I had to retard the timing.

platimus are cheap.. just slap some back in? The inlines are sensitive however... hanging onto crud until chemistry is feeding the vents. The classic design must be a better choice? stay solid for the debris..

boxers do not need it. I am bragging.

It is the stock semi-electronic ignition. It has a distributor, but it is electronically actuated (distributor cap has some huge contacts, so the computer can decide when to fire it).


But... yeah.... stock ignition:rolleyes:

Interesting results!
I quess you measured the vacuum at idle?

Did you notice any difference in RPM?
I'm just quessing, but maybe different gaps causes different ignition advance and that causes different rpm and also different vacuum:confused::rolleyes:

...some dated, but still very relevant, SAE articles worth reading:

SAE 690018, "Inlet Manifold Water Injection for Control of Nitrogen Oxides - Theory and Experiment," by J. E. Nicholls, I. A. El-Messiri, and H. K. Newhall, Dept. of Mechanical Engineering, University of Wisconsin, 1969.

SAE 700081, "Spark Plug Design Factors and Their Effect on Engine Performance," by R. J. Craver, R. S. Podiak, and R. D. Miller, Champion Spark Plug Co., 1970.

SAE 700532, "Milage Marathon from 50 to 244 mpg," by D. C. Carlson and H. D. Millay, Wood River Research Laboratory, Shell Oil Co., 1969.

SAE 710832, "Effect of Compression Ratio, Mixture Strength, Spark Timing, and Coolant Temperature Upon Exhause Emissions and Power," by R. C. Lee, Phillips Petroleum Co., 1971.

SAE 710835, "Effect of Engine Intake-Air Humidity, Temperature, and Pressue on Exhaust Emissions," by S. R. Krause, Ethyl Corpoation, 1971.

...also, try contacting Champion Spark Plugs and ask them about the "real" relationships and effects of gapping, compression ratio, and A/F-ratios.

Yes, the vacuum was measured at idle. The spark advance, EGR, and even idle speed are computer controlled, so I believe that the spark did change stuff, and then the computer compensated for it.

For those who are wondering, I am running a .040" gap now

And what is the manufacture's gap spec for your car? Thanks!

.035 inches

Dont be afraid of the big gaps guys, GM spec a .060 in 1975, they backed it down the following year but for FE it wont hurt you.