This is not a YJ specific question. But I spend most of my time on the the forum in the YJ tech section so I figured here is as good as any. Feel free to move this if there is a better section.
Yesterday I changed the plugs and wires on my wifes Ford Escort. It rolled over 139K with the origional plugs and wires. I already had some Bosch platinum 2 tipped plugs that I was going to use on the YJ before I read that they tend to go bad quickly in out engines.
Her car calls for a .054 gap, and these plugs claimed to be "pre gapped" but didn't say what they were gapped to. I checked them and they were set to .020. I figured that with the double tips it might equal out to .040 or something, but I wasn't sure. I just picked the middle ground and gapped them to .040 on both tips. But I have no idea if that is too wide or not wide enough. With the double tips does that equal .080 (the total width of both gaps combined) or does it just equal .040?
Also, this is what the plugs looked like. But I'm not very good at comparing them to the pictures in the repair manual. They all kind of look the same to me. Anything I should be noticing about these? They were gapped wider than my gapping tool would even go.
Nah, the gapping does not double just because there are 2 points. Set them at o50 all around on all the tips.
Wow those old ones are the most worn-out plugs I ever saw. BUT NOTICE #2 and #4 seems to be a bit cleaner than the others - It might have been running a bit hotter on that plug for some reason. Notice how all those electrodes are completely rounded over. I would save them for a trophy and just look at em every now and then.
Doesn't a wider gap help it to run better though? Or does it not matter that much?
A wider gap will increase the voltage required to fire the plug. Modern ignitions like this can do that. This means the ignition is more reliable under all conditions. A higher voltage spark jumping a wider gap will hit more gas molecules and give a better ignition. But ultimately how hot it is comes down to what the coil can do. You've got some leeway here. I wouldn't go any tighter than 040 where they're at now. But back in the 70's both ford and chevy could run 060. So you could easy do 060 on this and it would be fine.
So if you feel like pulling them and re-gapping them them by all means do it. But I'm just lazy.
Since the gap size has a direct affect on the spark plug's tip temperature
and on the voltage necessary to ionize (light) the air/fuel mixture, careful attention is required. While it is a popular misconception that plugs are pre-gapped from the factory, the fact remains that the gap must be adjusted for the vehicle that the spark plug is intended for. Those with modified engines must remember that a modified engine with higher compression or forced induction will typically require a smaller gap settings (to ensure ignitability
in these denser air/fuel mixtures). As a rule, the more power you are making, the smaller the gap you will need.
A spark plug's voltage requirement is directly proportionate to the gap size. The larger the gap, the more voltage is needed to bridge the gap. Most experienced tuners know that opening gaps up to present a larger spark to the air/fuel mixture maximizes burn efficiency. It is for this reason that most racers add high power ignition systems. The added power allows them to open the gap yet still provide a strong spark.
With this mind, many think the larger the gap the better. In fact, some aftermarket ignition systems boast that their systems can tolerate gaps that are extreme. Be wary of such claims. In most cases, the largest gap you can run may still be smaller than you think.
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This is for racers only !!
Indexing refers to a process whereby auxiliary washers of varying thickness are placed under the spark plug's shoulder so that when the spark plug is tightened, the gap will point in the desired direction.
However, without running an engine on a dyno, it is impossible to gauge which type of indexing works best in your engine. While most engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve.
In any case, engines with indexed spark plugs will typically make only a few more horsepower, typically less than 1% of total engine output. For a 500hp engine, you'd be lucky to get 5hp. While there are exceptions, the bottom line is that without a dyno, gauging success will be difficult.