Keith- I am going to disagree with you a little bit about the hotter larger spark. If it was as simple as ypu stated “as long as it ignites the mixture”, engineers would never resort to dual spark plugs for some engines. But you knew that or you wouldn’t have added “in most cases”
oldtimer 11, dual sparkplugs are a special case. Not the same as dual anode plugs either. By starting the flame front from two different locations, pressure builds up quicker in the cylinder. That is useful at very high RPM but could be counter productive at low RPM. Ideally only one plug would fire at low RPM and both at high RPM.
Nissan used them on some 4 cylinder pickup truck engines to cure a rough running engine design.On some engines the flame front spreads too slowly to combust all the fuel at the proper time. A larger hotter spark can help without the expense of dual plugs. If a hotter spark wasn’t better, why would we have gone to higher voltages and amps to fire plugs in the first place?
I guess I was not clear. Sometimes due to design, you do need a hotter spark or you get misfires. But if you don’t need the hotter spark, then a hotter spark doesn’t add anything. As engines are being pushed to the limit on a lean A?F mix, a hotter spark is needed.
I’ll also add to the center electrode clarification. A look at the NGK part number codes chart attechd willl show that the split center electrode has a different last alpha code than the solid center electrode. The “A” and “B” designations are used to designate that the sparkplug design is tide to a “specification control drawing” in the engine manufacturer’s design package. The car will come with an “A” or “B” plug, but the OEM replacement plug will be coded differently. It took me a bit of research combined with years of experience working with design packages to find out why I could not get the exact part number that the car came with.
This chart should clarify some questions.
That is an interesting post. If you trim off the techinfo… you get to the home page, then click on the spark plug link. This was the first time I had actually seen the tip of the V power plug and it was not how it was described. Instead of trimming back the ground electrode, they notch a groove in the center electrode. It has the same effect of concentrating the corona at the edge, thus giving a hotter spark.
BTW, to the OP, if you peruse around the site, you will see references to hotter and cooler plugs, that is not the same as hotter spark. Spark plug tips need to maintain a certain temperature to prevent deposits from building up on them, but if they retain too much heat, they will burn up the ceramic insulators. Sometimes if your driving conditions warrant, you have to switch heat ranges, for example if you do a lot of highway driving, you might need a cooler plug. But if your old plugs didn’t have damaged insulators, then you are OK.
I also see that they sell a racing plug, which they do trim back the ground electrode somewhat as I described. I wonder how much they charge for that little service.
A bunch I’m sure. That’s probably a hand operation after manufacturing. I doubt the volume is sufficient to do otherwise.
It’s a great site. I agree with your suggestion to the OP to peruse the site. It’s very informative.
Another thing which could have happened is that you cracked a plug wire. This vehicle has had 10 years of very hot under the hood temps and maybe the plug wires are brittle. You may have cracked one wire inside and can’t see it, but it causes a misfire. If it’s a V-6 and you’re not getting spark to one cylinder you could (maybe) notice it, maybe not. But a misfire would cause your MPG to drop. The vacuum line is another good idea. Lastly, maybe you could visit a Toyota website for guys who play around with their rides, I’m sure they could suggest the proper or optimum gap for your plugs. Good luck! Rocketman
Keith, I agree completely with your last two posts.
Kettering, not kittering
OK
Isn’t the dual spark plug of value only to add extra insurance that gas molecules will exist in the path of the spark during the (short) time the spark occurs?
Dual spark plugs can start the burn in two locations.
That’s an advantage if the combustion chamber is an oblong shape, like in the Wankel (rotary).
That is one advantage, but there are others. The fuel air mixture that enters the combustion chamber consists of air, fuel drops and fuel vapor. Only the vapor actually burns, but once it starts burning, it raises the temperature in the combustion chamber so that the fuel droplets begin to vaporize faster.
Actually, it it had enough time, all the fuel droplets would turn into vapor, but from the time the fuel exits the injector as a mist, it just doesn’t have time to completely vaporize at ambient temperatures. The higher the temperature, the faster it vaporizes.
So back to ignition, the spark ignites the vapors and as they burn, the fuel droplets vaporize and it in turn burns, building more heat and more vaporization of the remaining fuel until the droplets are completely vaporized and burned. The vapor ignition starts as a flame front from the point of ignition and spreads out to all parts of the combustion chamber. So pressure builds up in the combustion chamber as the flame spreads and the droplets burn from the outside in.
Starting the ignition point in two separate places will create two flame fronts spreading the ignition to all parts of the combustion chamber a little faster. This is an advantage to the oblong combustion chamber as noted by circuitsmith, but it is also an advantage for engines with a large bore and short stroke as well as very high RPM motors.
It is difficult to get more than one spark plug into a multivalve cylinder though so you don’t see that technology used much. But there is potential that could be explored here.
I have a Chilton repair manual and it states that for 89-94 2.4L engines the gap should be .31