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Old 09-12-2012, 12:57 AM   #11 (permalink)
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I put Autolite Platinums in it, same as what was in it. Of course gapped correctly.

The ones I took out had widely varying gaps. Four looked quite good, two had pretty worn ground electrodes.

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Old 09-23-2012, 11:58 AM   #12 (permalink)
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It is probably too late for you, but...

Going back 35 years to my automotive training...

The whole point of spark plug heat range is to keep the plug hot enough to burn any deposits off of it without either burning up the plug or pre-igniting the mixture and suffering the resultant detonation. Interesting to note that some engines like Remote Control glowplug engines and top-fuel dragsters both rely on pre-ignition from the hot plug to keep running.

So the right temperature is about 500f if I recall correctly. If the plug is at that temperature it will just be on the verge of pre-ignition, and it won't take much spark to fire it off. If it is cooler, it will take a strong spark to fire the mixture and there may be occasional misfires, which means fuel wasted and an O2 sensor that turns up the richness on the mixture to compensate. So you have to keep the plug up near 500f.

The problem is, when you are just loafing around, like we do when we are trying to save gas, the plug stays too cool. The temp range is chosen for WOT (wide open throttle). Now for a fact if you are racing or pulling a trailer up Pikes Peak, you would want colder plugs in your engine, and it is often done. We however, want a sure ignition while loafing around 98% of the time. Our use of full throttle is very rare and only momentary at that. If you can stand the risk (of WOT use), you could benefit from hotter plugs, at least theoretically.

I have in thepast switched to hotter plugs to get a lean mixture to ignite at light loads and did see a fuel mileage and driveability improvement. YMMV.

So, how do you know what plug to run?
Well, for maximum power we run them at WOT for a while and then pull them out to look at the colour of the insulator. White is baked too hot, light beige is perfect and black is too cold, (or too rich, but this isn't meant to be an all encompassing lesson). So if you pull the plugs out of you car after routine driving and they are black, you are running too cold. Gas and combustion products are being deposited on the cold plug insulator and most likely the engine is misfiring and wasting fuel. You need a plug heat range that puts the beige back into your insulator if you want consistent ignition.

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Old 09-23-2012, 12:24 PM   #13 (permalink)
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that car should be in the 30+ mpg range if it is anything like the first gen 1987 I drove, it got that. My father in law owned it from new ,so it was well maintained. Plugs Platinum (open the boxes and make sure the electrode is not the small dia. wicker type ) and when you pull the plastic intake to change the plugs take the time to stuff the intakes with clean paper towels before anything else is done
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Old 09-23-2012, 12:46 PM   #14 (permalink)
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Egad, I got this post mixed up with one on heat range.

Yes, spark plug types, advantage? Well, platinum is proven.
And did you notice some of the platinum plugs that came with the car have platinum only on one electrode and half of them have it on the other? Has to due with electron flow and erosion in the dual plug coils and the manufacturer being able to buy single tipped plugs cheaper than dual tipped platinums. Look at the number on the OEM plug, it has an odd suffix and the catalogs don't even mention it, we cannot buy them, manufacturer only.

So platinum is proven as an erosion resistant material, and the iridium is supposed to be even better, but perhaps the electrode would then outlast the insulator and the threads electrolytically corroding into the heads. Maybe we should stick with platinum and change then every few years just those 2 items sake?

What about the copper and silver cores? Gotta be better than carbon cores? I mean like carbon is a resistor, right? Well, it all has to do with high voltages, very little current flow, radio suppression and a whack of other things, but basically, no, copper and silver cores do not help. A carbon core actually helps to build up higher spark voltages and hotter spark as well as dampen radio interference. No magic bullet in core or electrode types other than what the manufacturer specified unless you have highly modified the engine some strange way.

Cheap plugs are made of cheap materials and have bad things happen. Electrodes fall off, insulators carbon up easily, electrodes wear. No bargains in off brand plugs and made in China look-alikes.

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Old 09-29-2012, 02:50 PM   #15 (permalink)
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Quote:
Originally Posted by ConnClark View Post
The only thing that would improve mileage as far as sparkplugs go is having more than one per cylinder. Ask any pilot of a piston engine plane that does a magneto check on warm up. They will tell you that they get more power running off both sets of plugs than they do running on one set using the exact same throttle setting. This is due to a faster flame propagation through the cylinder from sparks starting in separate locations. Note, multi electrode sparkplug (3 or more) do not have the same effect because the spark only goes between the center and one of the other electrodes.
Alfa-Romeo's have (or had) Twin-Spark engines. These engines were attached to some very nice looking, and nice to drive cars which would fall apart very quickly due to lack of dealer interest.
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Old 09-29-2012, 06:08 PM   #16 (permalink)
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My belief is, that the spark energy comes from the ignition coil, not from the spark plug.
The gap in the spark plug determines how the energy is used.
if the gap is "small" then the spark will start a bit earlier and burn longer.
But if the gap is "big" then it takes a bit more time to have enough voltage across the gap before the spark can jump and the spark burn time will be a bit shorter.
In both cases the energy is the same.
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Old 09-30-2012, 10:55 AM   #17 (permalink)
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Quote:
Originally Posted by Arragonis View Post
Alfa-Romeo's have (or had) Twin-Spark engines. These engines were attached to some very nice looking, and nice to drive cars which would fall apart very quickly due to lack of dealer interest.
First generation Fits outside the US came with 1.3 liter dual spark engines with CVTs. Fantastic little cars, capable of 60 mpg on the highway and up to 70 mpg hypermiling WITHOUT EOC.

Took the pkugs out of one a while ago. The tips were the expected dark reddish, while the post of the electrode was slightly white. Perfect lean burn. And the motor ran perfectly fine on regular unleaded.
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Old 09-30-2012, 04:47 PM   #18 (permalink)
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Other engines have had dual spark plugs. My wife's V8 Benz has 16 spark plugs--talk about a royal pain to change!

I know that in the aircooled Porsche world, it is used to allow higher compression than with the single plug setup. The second plug is placed symmetrically with the original plug. The general rule of thumb is that you can run a full point compression more on the same fuel with twin plugs as with single.

That is highly dependent on combustion chamber shape, though. The wedge-shaped aircooled VW heads benefit much less than the somewhat-more-hemispherical 911 combustion chambers.

One friend of mine remarked that dual spark plugs are a band-aid to help suboptimal combustion chamber designs run more compression... I'm not sure he's wrong!

In other applications, such as aircraft, the dual plugs are there only for redundancy. They are typically run by completely separate ignition systems such that if one component fails there is a separate system still doing the work.

-soD

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