what's this,4 cyl-8 spark plugs!why? - Vintage Mustang Forums

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post #1 of 10 (permalink) Old 09-19-2002, 10:24 PM Thread Starter
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a friend bought a 92 mustang for his daughter,i'm standing there looking at the 2.3 4 cyl.and happen to look at the plug wires,there's 8 of them,when did they start this in the 2.3 what is the point,one plug fires,gas explodes,pushes piston down.it don't matter how many sparks ignite the fuel it only has so much energy to expel.this was a new one for me maybe everyone is using 2 plugs per hole now and i'm still locked in the 1980's.someone got a explanation........ i'm thinking about going out and drilling 3 holes in each cyl. in my 428 just so it can take 8 hrs to change the plugs instead of 3.

THE ONE WHO DIES WITH THE MOST TOYS WINS and so far i'm losing...
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post #2 of 10 (permalink) Old 09-19-2002, 10:30 PM
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My brother has a 89 ranger with the 2.3 L and it has 2 plugs per cylinder. Runs good. John
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post #3 of 10 (permalink) Old 09-19-2002, 10:39 PM
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I looked up the system in the Ford shop manual and it states "One plug in a cylinder fires in the compression cycle and the other plug fires during the exhaust stroke". John
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post #4 of 10 (permalink) Old 09-19-2002, 10:39 PM
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My understanding is that the twin plug head was used to gain better combustion. The design allows the flame front to be initiated at two locations. I have no idea whether it worked. I believe Ford started using it in the early '90s.
The previous post about one plug firing on the dead stroke is news to me. I have no idea what the benefit of firing on the off stroke would be.


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post #5 of 10 (permalink) Old 09-19-2002, 11:16 PM
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Either way, The new Dodge 5.7 litre Hemi has 2 plugs per cylinder for a total of 16..... so there must be somthing good about it, specially since that thing is putting out 345 hp.

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post #6 of 10 (permalink) Old 09-19-2002, 11:19 PM
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"I looked up the system in the Ford shop manual and it states "One plug in a cylinder fires in the compression cycle and the other plug fires during the exhaust stroke".

Now im not sure about this system but ford uses a " wasted spark" coil pack type ignition that uses 2 coilpacks to fire 4 cylinders. Now you have 1 coil that fires 2 cylinders at the same time so when the coil fires it sends spark to 2 cylinders at once instead of one . The only way to safely send spark to 2 cylinders at once is to fire the coil while one of the cylinders is on compression and while the other is on the exhaust stroke hence the title wasted spark. Still not sure where the 2 plugs come in but im thinking it has something to do with overheating the plugs? If you fire one plug 2 times during one cycle of an engine it might cause heat problems ?Only reason i can think of at the moment...
post #7 of 10 (permalink) Old 09-20-2002, 12:07 AM
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I have a feeling it reduces the emissions coming out the tailpipe. Whether it fires on the exhaust stroke or a little bit after the primary spark, it will ignite whatever fuel and air is left in the cylinder and that will siginificantly reduce the hydrocarbon output of the engine. The Feds like that sorta thing. They don't care if it makes more power, just as long as it doesn't pollute.

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post #8 of 10 (permalink) Old 09-20-2002, 12:39 AM
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It's just a pollution thing. The guys pumping up their SVO's have found the "8 plug" heads to be fairly useless for a couple of design reasons. AND the extra plugs are useless for power purposes. Nissan did the same thing on 80's Pickups and 200SX engines. No appreciable power difference between 4 plug and 8 plug there either.
For many, many years Harleys have run a "waste spark" too. Nothing to do with pollution, it was just easier and cheaper to build them that way. The waste spark has no purpose nor effect on the running of the engines. For a while the big thing was to modify the heads for dual plugs. The plugs fired together and the waste spark was still produced. This is almost unheard of now since it's only REALLY useful for dragracers running nitromethane or alcohol. There are now some kits that eliminate the waste spark and allow individual cylinder tuning. The value of these kits has yet to be really proven beneficial, at least to me.
The only street engine I know of that really benefits from dual plugs is the Mazda RX7 type rotary engine, especially if they're turbocharged.

.... it wouldn't be the first time reality took theory and conjecture out behind the woodshed and gave them a good thrashing.
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post #9 of 10 (permalink) Old 09-20-2002, 10:05 AM
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It is common for light aircraft to have twin spark plugs per cylinder. The also have twin magnetos. I think it is more of a safety thing. Also, some of the older Porsches have twin spark plugs. In the Porsche case, it was a performance enhancement. But for the 2.3 litter Ford, I assume (like the others said) is for pollution control. I assume you could run a cam with a lot more overlap and still be clean. If it really works then I would assume all newer cars would have them and if was just a good idea that did not really work then it will just fad away. Sounds like the later is happening.

66 Fastback GT with long rod roller cam 302 and T5 trans. On the street and still needs a lot of work.
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post #10 of 10 (permalink) Old 09-20-2002, 05:01 PM
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emissions and added power....one fires in rapid sucession to the other....this means a better power band and a built in MSD type firing of the ignition...multiple spark discharge of a sort...

re:2 plugs per cylinder

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