Spark Plug Wires

[gthyni]

If the resistances is in serial that gives:

5 + 5 + 5 + 5 = 20 ohm

if cables and plugs are 5 ohms each.

 

if in parallell:

((5 + 5) * (5 + 5) ) / ((5 + 5) + (5 + 5)) = 100 / 20 = 5 ohms

 

a third option would be to have 2 colis in one box

in which case in would be no different from a single plug

system.

 

You don't get a weaker spark on the 2nd plug,

you get a equally weakened spark on both plugs.

[al_roethlisberger]

Sure, I understand the series and parallel issue, my question is whether or not just one resistor plug or one resistor wire(cap) is sufficient for the 2 plug and 2 wire "loop" to and from the coil In other words does the entire "loop" just need 5k Ohm resistance, regardless of where that resistor "sits" to keep EMI under control.

 

You don't get a weaker spark on the 2nd plug,

you get a equally weakened spark on both plugs.

 

With all due respect, I don't think this is quote correct... well, yes it's correct electrically ...but what I mean/meant is that the second plug will have two things working against it.

 

1) Some spark energy will be lost to ground and resistance through the engine head/block as it travels from the negative electrode on the first plug, to the negative(now actually "positive") electrode on the second plug.

 

2) The second plug is also firing "backwards" arcing from the "negative" electrode to the tip of the plug, which is was not designed to do. This will also be a barrier to an efficient spark, as the plug inherintly wasn't designed to do this. How much will this matter?? Good question. Probably not much, but just something to realize when using a "lost spark" system.

 

So I believe, and based on speaking with a number of tuner guys, that the spark on the second plug will be a bit weaker, but it will work fine.

 

To your point about using a different type of coil-pack that doesn't have this issue, yes that could be done. And in fact, this was what I was looking at doing, that is buying an aftermarket coil that actually has two coils in the pack and independently, but simultaneously fires that cylinder's two plugs. However, I would have had to fabricate a connector, or hack into the stock wiring harness to do this, and this is something I wanted to avoid, hence my earlier post in the "For Sale" section looking to buy some used coils to cannibalize the connectors

 

Anyway, when I found the OEM dual-output coils from MM that would be "plug and play" I was willing to sacrifice some efficiency for the convenience and reliability these offered.

 

...oh, and BTW, keep in mind that I'm still not 100% sure that they MM dual-output coils indeed are "lost spark", but then again, I'm pretty sure they are just from my conversations. We'll know soon enough though

 

And of course, I could just be wrong about everything I wrote above ...as it's all hear-say at this point! I'll let you know what I find out.

 

al

[jtucker]

Hmmm... if this coil is "lost spark" as you say, then I'm not sure if I would want it or not. I like the idea of the dual-plug setup providing some fault tolerance, in addition to performance. In other words, I would *like* to be able to run on a single plug if I need to...

[al_roethlisberger]

Hmmm... if this coil is "lost spark" as you say, then I'm not sure if I would want it or not. I like the idea of the dual-plug setup providing some fault tolerance, in addition to performance. In other words, I would *like* to be able to run on a single plug if I need to...

 

 

Yes, that is true... however one could easily "clip" one of the wires to the head and all would be well, so you would still have your redundancy even if you broke one plug "clean off"

 

Obviously, a "lost spark" system isn't the best choice in regards to efficiency, but it is the most economical for most coil makers to build, and other than your mishap ... how often does the scenario for most bikes occurr where this sort of physical redundancy is needed for a spark plug or coil? Probably pretty rare, except in our case. So most OEM solutions use this method.

 

But again, I think that it still works... you would just have to clip/bolt/affix one of the cables with the broken plug to the head, and it would work fine.

 

al

[dlaing]

I thought a lost spark was when it sparked not only at just before TDC of compression but also at another point.

Like on parallel twins with one coil it would fire simultaneously on both the left and right cylinders, so that it would alternate firing at about TDC of compression and TDC of exhaust or some other point in the cycles.

Anyway, I did not know that a pair of plugs could be run in series like that....pretty neat!

In that case ignore my previous comments...not that it would not work, but I think that you are correct that 5kOhms should be enough suppression for two resistorless plugs in series.

And if the coils are the same size as stock, you may have to also shorten the spark plug gaps because you may be getting less voltage???????

Or get an ignition booster???

Can you tell which high voltage terminal is Positive? It may make more sense to put the resistor on the positive side so that the Negative side does not have to compete as much against the ground of the bike.

Serial plugs seems pretty voodoo to me, but if it works, will there you go!

[al_roethlisberger]

Hrmmm, yeah... you could be right on the terminology... "wasted spark", "lost spark", "single fire", "dual fire"... it gets confusing after a while

 

 

But just to avoid confusion for now, let's just go with the "lost spark" term for now to describe the "serial fire" dual plug setup

 

And yes, you are correct that one may have to squish the gap a bit, or "boost" the ignition. But the advantages are still there.

 

I'm sure I'll have to play with it a bit at first, but then again the guys at TLM said that they kept the timing, gap, etc... all stock, and it ran like a clock. So who knows. They have apparently sold several of these conversions, so I'll defer to their expertise for now

 

al

[al_roethlisberger]

Some interesting info from Mike Rich:

 

Hi Al - I think you've been misinformed about how ignition coils work - both sides of the coil fire simultaneously . The principle is as follows - There are 2 sets of windings in every coil - the primary and the secondary  -when the primary winding is charged it excites the electrons in the larger secondary ( this is when the voltage steps up and amperage steps down) When the ECU triggers the coils to fire it simply grounds the primary coil and the secondary coils current seeks ground - (The spark plug ) and fires the Engine. Usually the dual fired coil is designed with a single primary winding and  either one large secondary -that seeks ground from both end of the winding - or the more complex dual secondary windings that are wound around a single primary. In all instances that I'm aware of you can only fire a spark plug by making the current seek ground - through the path of least resistance - (your spark plug wires) There is more to this ( coil saturation time ect.....)But this is meat and potato's of it.  -----  To answer your other questions - you need dual resistor plugs - and caps ... It will not effect the spark energy to any appreciable degree - and your ECU will love you for it!  Remember - do not turn your Guzzi"s ignition on without properly grounded spark plugs connected to the plug wires! It can damage your ECU!

                                                                              Regards Mike Rich

 

al

[callison]

My old Honda 350/4 had two sets of dual output coils and two sets of points. The coils were connected such that the outputs would fire the cylinder under power (compression) as well as it's balance mate 180˚ degrees out on the exhaust stroke. The spark in the exhaust stroke is the "waste " spark as it doesn't provide anything to the combustion process. The point here is that it only took two sets of points and coils to fire a 4 cylinder engine. I believe this a pretty standard approach for parallel 4 cylinder bikes. I talked to someone, can't remember who, and a waste spark on a Guzzi engine is also harmless, so ignore it and concentrate on the basics. The dual output coil needs to have a load on each of the spark leads or the voltage developed when the primary field collapses will be high enough to destroy the insulation - ruining the coil (same for a single output coil). So I would say, don't attempt to test it, hook it up correctly and assume that it's going to do it's job in the same fashion as a single output coil. It is for this reason that you do not make the spark plug gap too large. If the arc resistance is higher than the insulation punch through, the voltage will seek the easier of two paths and punch through the insulation ruining the coil. Too small a gap, and the spark loses effectiveness. Manufacturers specifications for spark gap measurements reflect the choices of the coils quite effectively. The other things that can affect spark gap resistance, such as high combustion chamber pressure, are not likely going to be approached by a streetable engine, so I would discount their effect on the discussion. Today's word is bifilar. This is how ignition coils are wound as opposed to the standard transformers you find in the power supply to your stereo.

[dlaing]

So if there is no manufacturer to determine gap and resistance figures, what should Al do for his dual plug set up?

[callison]

Use the stock gap. The coils are from the same manufacturer and are built in the same way, they just have another winding in them is all.