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Re: New Coil

Subject: Re: New Coil
Date: Sun, 9 Aug 1998 15:22:15 EDT
In a message dated 98-08-09 00:56:08 EDT, writes:

>    Assuming there is suffecient capacity to operate the plugs at 5000 RPM
>  (which in too may cases with original equipment is not true), and thus
>  "excess" capacity at lower RPM, then the whole reason for High Capacity
>  coils (such as the Lucas Sport coil) no longer exists. Yet, listers and
>  others who have installed such a coil do report advantages. Stronger
>  spark, allowing wider gaps etc, etc etc.

Can't argue with that. If the stock system is good enough, no need for the
high capacity coil. If the new coil gives performance gains, then I think it
is safe to say the old coil was NOT adequate.
>      If by simple act of checking the connections of the coil (a 10 second
>  operation) you could avoid any suppoised inefficiency, why would any
>  thinking person do so? 

Assuming you meant to say NOT do so, I can't think of any reason, yet we see
it often.
>    You can see the results on a Dyno. It's real

I'll accept that.
>  Just because you never use the engine to the max, is no reason to not
>  have the ignition system in tip-top order, or indeed any system on the
>  car.

Can't argue with that.
>   Nor do I. But then again, I don't have an elevator in my GT :>)

What, no elevator? How do you get to the second floor?  

>    If they use washers, they aren't mechanics on the cars up front.
>  Besides, washers won't work on tapered seat plugs, which are found in
>  most modern cars.
>   The proper way is to test each of a handfull of plugs in each plug hole,
>  selecting the one that places the side electrode in the proper position.
>  On a 4 cyl engine, I've rarely had to use over 7 plugs to get a set.
>  Usually it's 5 or 6. Got lucky once and did it with 4.

Agreed, yet many mechanics still use the washers, and many "experts" still say
to do it that way. I don't compete with either of my cars, so I haven't used
either approach.
>     Hooking up the coil correctly is one of those things that is done,
>  like hooking up the battery correctly.  It's just routine  to hook it up
>  correctly. You don't even think about it.

Agreed, if you know which way is correct. Usually, the only time this is a
problem is when someone converts from positive to negative ground. In the 2
years or so that I have been on this and the Triumph list, this question has
come up at least a dozen times. To those who haven't studied automotive
electricals, coil polarity is not intuitive. As a matter of fact, there are
places on the WWW with incorrect instructions for this.
>      Indexing of the plugs will give a marginal performance gain, which
>  will vary with a particular engine, but usually (assuming a 100 HP
>  engine) of 1 HP or so. Granted, the gains generally are in the upper RPM
>  range, and for the driver/owner who never gets his MG above 3500, no real
>  improvement. There is one other advantage to indexing the plugs, and that
>  is the placement of the "open" side of the plug facing the intake valve,
>  results in a plug that will stay cleaner, longer as the incoming charge
>  sweeps across the center electrode with the least interference which
>  tends to scour the electrode faces, keeping them somewhat cleaner. Also,
>  the incoming charge, being relatively cooler, will lower the temperature
>  of the electrodes, which (as I understand these things) reduces the
>  resistance, and thus making it easier for the spark to bridge the gap.

Sounds good to me!
>      I don't know what Barney will point you to, Dan, but, for starters
>  check out any service manual for any GM car with dual lead coils (Grand
>  Prix, Beretta, etc)
>   Then just for funsies, look under the hood and trace the coil leads from
>  any dual lead coil to their respective plugs. You will notice that the
>  two plugs are exactly 180 degrees apart on the firing order. Ie. one is
>  on compresion/firing stroke, the other is 180 degrees different, on the
>  exhaust stroke.
>   Finally, check out a coil itself. You will notice that (1) there is no
>  switching system to direct the coil output to one or the other tower and

Let me clarify my doubts on what Barney said. I don't doubt that the two plugs
fire at the same time, 180 degrees apart. I am familiar with that technique.
What I do doubt is the statement that the plugs are wired in SERIES with each

>  (2). the wiring diagram (from either a Haynes manual or other source)
>  will show the two HT towers are internally wired together. 

If the internal HT towers are wired together, then the plugs are wired in
parallel, not series. Both plugs fire at the same time, but the current
doesn't flow from the tip of one plug to ground, through ground to the other
plug gap, and then back to the coil. Current flows through both plugs to
ground, and then back to the coil. Current flow through each plug is
independant of the current flow through the other (or very nearly independant
- TOTAL current flow from the coil impacts the output of the coil, which will
impact current through both plugs).

Dan Masters,
Alcoa, TN

'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74

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