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I'll chime in here (as is my wont). I'm not an EE--my electrical
knowledge is self-taught--so if I'm incorrect feel free to correct.<br>
<br>
The theoretical output of a coil--which is essentially half of an AC
transformer--is determined by the ratio of its secondary winding to
its primary. For example, a coil with 10 primary windings and 20,000
secondary windings will boost the primary 'signal' 2,000 times, so
it would boost a primary signal of 12V to 24,000 volts. When the
primary pulse to the coil is discontinued--e.g. points open--both
the primary and secondary induced electrical fields collapse, and
the secondary field is directed to the plugs*. The secondary field
collapses until it produces sufficient voltage to overcome the
resistance of the plug gap; hence the width of the gap determines
the strength of the spark. For example--pulling numbers out of my
exhaust pipe--if a 0.025" gap requires 10K volts to produce a spark,
then a 0.030" gap might require 12K volts to produce a spark. So, a
larger gap produces a 'hotter' spark, up to the theoretical limit of
the coil, and a hotter spark is better, no? Well, yes and no;
theoretically, as long as the spark is hot enough to jump the gap it
will ignite a proper mixture. A very lean mixture is harder to
ignite, and a very rich mixture could 'drown' the spark ('stratified
charge' engines use a richer mixture to ignite a leaner mixture). A
hotter spark may more reliably ignite a non-ideal mixture, and may
help a bit to ignite a proper one (higher compression engines
require a hotter spark). But, as Josef noted, since every spark
transmits some of the non-ground electrode--probably billions of
atoms--to the ground electrode a hotter spark will erode the
electrode faster (since erosion starts with the first spark and with
a wider gap you should re-gap more often). Note condensers
(capacitors) are used in points systems and SU fuel pumps to
suppress spark arcing and subsequent points erosion. Which is why
...<br>
<br>
Exotic metal--platinum or iridium--plugs are more resistant to
erosion, which is why newer cars can go 80K miles or more without a
'tuneup,' which, for all intents-and-purposes just means swapping
plugs (note they come in 'single' (default) or 'dual' types, meaning
one or both electrodes are the exotic metal, respectively) .
Old-style plugs with copper and steel electrodes can reliably go 15K
miles or more, with one or two re-gaps, so exotic metal plugs aren't
particularly useful for our cars which might do a couple thousand
miles a year but, hey, knock yourself out. Note that platinum and
iridium plugs come pre-gapped, and you'd best not mess with them.
When I swapped plugs on my '08 Mustang I couldn't find a gap spec
anywhere, but IIRC I futzed with them anyway (of course) and think
they were all about 0.025". Fortunately, the car still ran well
after my meddling and I traded it in in a few years anyway.
Curiously, I watched a David Vizard video where he claimed he saw a
<i>slight</i> mileage increase using E3 'DiamondFire' plugs, so
there may be something to the plug voodoo. Fun fact: All the iridium
on planet Earth came from a single asteroid, and is found in a layer
of said earth deposited around the same time the dinosaurs went
kaput. Coincidence? I think not.<br>
<br>
Anybody who's worked on 'modern' cars, say, newer than 2000MY or so,
has noted 'Coil On Plug' ('COP') technology, where each plug get its
own coil. Now, the coils on these are small, about the size of an
old 35mm film canister--remember those?--and you might say to
yourself 'Self, how do they stuff all that wiring into that little
film canister' and the answer is, the wires gotta be real tiny and,
yep, as you might expect they are fragile compared to our Bud Light
can-sized (sorry) old school Lucas coils. Early COP systems--looking
at you, VW--were prone to gremlins and I still hear about COP
failures on newer cars and other makes, esp. with DOHC engines which
always, eventually, seem to get leaky valve cover gaskets which dump
oil into the plug tubes (as opposed to leaky Healey valve cover
gaskets which just dump oil, well, everywhere).<br>
<br>
OK, caffeine rush is fading. Ciao.<br>
<br>
Bob<br>
<br>
* Note coils for our Healeys come with either 'SW' ('switch;' i.e.
ignition switch) and 'CB' ('contact breaker;' i.e.
points/distributor) or '+' and '-' labels on the primary terminals.
They'll work either way, but some voodoo is employed whereby, when
properly connected the secondary field is routed in series with the
primary circuit to give a slight boost to produced spark.<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 5/4/2023 4:43 AM, josef-eckert---
via Healeys wrote:<br>
</div>
<blockquote type="cite"
cite="mid:1683200618943.30241.4931512a23c5af4193aff3855654c40b0b67018f@spica.telekom.de">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title></title>
<p style="margin: 0px;"><span
style="font-family:arial,helvetica,sans-serif;font-size:10pt;color:#000000;text-decoration:none">Sorry,
I am out here. This guy wants to play till the engine is shot.<br>
</span></p>
<p style="margin: 0px;"><span
style="font-family:arial,helvetica,sans-serif;font-size:10pt;color:#000000;text-decoration:none"> </span></p>
<p style="margin: 0px;"> </p>
<p style="margin: 0px;"> </p>
<p style="margin: 0px;">-----Original-Nachricht-----</p>
<p style="margin: 0px;">Betreff: RE: [Healeys] Spark plug gap</p>
<p style="margin: 0px;">Datum: 2023-05-04T12:45:37+0200</p>
<p style="margin: 0px;">Von: <a class="moz-txt-link-rfc2396E" href="mailto:simon.lachlan@alexarevel.plus.com">"simon.lachlan@alexarevel.plus.com"</a>
<a class="moz-txt-link-rfc2396E" href="mailto:simon.lachlan@alexarevel.plus.com"><simon.lachlan@alexarevel.plus.com></a></p>
<p style="margin: 0px;">An: <a class="moz-txt-link-rfc2396E" href="mailto:josef-eckert@t-online.de">"josef-eckert@t-online.de"</a>
<a class="moz-txt-link-rfc2396E" href="mailto:josef-eckert@t-online.de"><josef-eckert@t-online.de></a></p>
<p style="margin: 0px;"> </p>
<p style="margin: 0px;"> </p>
<p style="margin: 0px;"> </p>
<div style="position: relative; color: #000000; font: 12px
Arial,Helvetica,sans-serif;">
<div class="WordSection1">
<p class="MsoNormal"><span style="mso-fareast-language:
EN-US;">Thanks for that. I’ll certainly bear it in mind.
Likewise, I’ll keep a close eye on my engine’s
temperature. The latter is quite well protected with a
modern rad, all the correct baffles, 5 blade fan plus
electronic fan. But, as I said, I’ll keep an eye on it.</span></p>
<p class="MsoNormal"><span style="mso-fareast-language:
EN-US;">Someone mentioned that he used “Iridium” plugs
from NGK. I googled them….horribly expensive. Can they be
worth it in our old cars?</span></p>
<p class="MsoNormal"><span style="mso-fareast-language:
EN-US;">Simon</span></p>
<p class="MsoNormal"><span style="mso-fareast-language:
EN-US;"> </span></p>
<div>
<div style="border: none; border-top: solid #E1E1E1 1.0pt;
padding: 3.0pt 0cm 0cm 0cm;">
<p class="MsoNormal"><strong><span lang="EN-US">From:</span></strong><span
lang="EN-US"> <a class="moz-txt-link-abbreviated" href="mailto:josef-eckert@t-online.de">josef-eckert@t-online.de</a>
<a class="moz-txt-link-rfc2396E" href="mailto:josef-eckert@t-online.de"><josef-eckert@t-online.de></a> <br>
<strong>Sent:</strong> 04 May 2023 07:06<br>
<strong>To:</strong>
<a class="moz-txt-link-abbreviated" href="mailto:simon.lachlan@alexarevel.plus.com">simon.lachlan@alexarevel.plus.com</a>; Healey, Forum
<a class="moz-txt-link-rfc2396E" href="mailto:healeys@autox.team.net"><healeys@autox.team.net></a><br>
<strong>Subject:</strong> AW: [Healeys] Spark plug gap</span></p>
</div>
</div>
<p class="MsoNormal"> </p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">For me, i
prefer Champion plugs plugs to NGK, but that´s a matter of
taste. I think both, Champion and NGK, are of similar
quality. Matter of taste, as I wrote. But NOT the car
manufacturer determines the plug gap, its the plug
manufacturer. Definitely the car manufacturer takes this
for his specs in the workshop manual.</span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">There is
to much hype about plugs anyway. I am working as a
professional, Elecrtonics and Elecrtrcian engineer, at a
big classic car parts supplier here in Europe and I never
go away from the given plug gap as set by the plug
manufacturer. Austin-Healey engines are not high tech,
they are tractor engines and can take a lot of misfit, but
anyway BMC knew at the time what´s best to do with them,
even its printed 60 or 70 years ago.</span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">Some
people try to adjust the fuel mixture with a CO-tester.
You can do that, but it doesn´t give best results for road
use, especially in hotter climates and high above sea
level. </span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">When you
are very good in engine engineering and have all the tools
you can try to find some more horsepower in your engine,
but you always pay that with some more heat produced,
which is not at all good for our old BMC engines.</span></p>
<p style="margin: 0px;"> </p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">Josef</span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;"> </span></p>
<p style="margin: 0px;"> </p>
<p style="margin: 0px;"> </p>
<p style="margin: 0px;">-----Original-Nachricht-----</p>
<p style="margin: 0px;">Betreff: RE: [Healeys] Spark plug gap</p>
<p style="margin: 0px;">Datum: 2023-05-04T00:06:58+0200</p>
<p style="margin: 0px;">Von: "<a
href="mailto:simon.lachlan@alexarevel.plus.com"
moz-do-not-send="true" class="moz-txt-link-freetext">simon.lachlan@alexarevel.plus.com</a>"
<<a href="mailto:simon.lachlan@alexarevel.plus.com"
moz-do-not-send="true" class="moz-txt-link-freetext">simon.lachlan@alexarevel.plus.com</a>></p>
<p style="margin: 0px;">An: "<a
href="mailto:josef-eckert@t-online.de"
moz-do-not-send="true" class="moz-txt-link-freetext">josef-eckert@t-online.de</a>"
<<a href="mailto:josef-eckert@t-online.de"
moz-do-not-send="true" class="moz-txt-link-freetext">josef-eckert@t-online.de</a>></p>
<p style="margin: 0px;"> </p>
<p style="margin: 0px;"> </p>
<p style="margin: 0px;"> </p>
<div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span style="font-size:
9.0pt; font-family: 'Arial',sans-serif; color: black;
mso-fareast-language: EN-US;">You may be right. Not
sure. </span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span style="font-size:
9.0pt; font-family: 'Arial',sans-serif; color: black;
mso-fareast-language: EN-US;">Actually I thought that
the gap was determined by the car’s manufacturer ie
one could expect to find the same plug in two
different cars and to find that the recommended gap
was not the same for each car.</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span style="font-size:
9.0pt; font-family: 'Arial',sans-serif; color: black;
mso-fareast-language: EN-US;">Likewise, the BMC manual
suggests Champion plugs at 0.024” to 0.026” and that
was some 60+ years ago. I’ve always been told that
Champion plugs aren’t the best in the world and I’m
sure that a modern NGK can stand a little more heat
than the Champions that were around 60 years ago.</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span style="font-size:
9.0pt; font-family: 'Arial',sans-serif; color: black;
mso-fareast-language: EN-US;">Anyhow, I’ll keep an eye
on them. I’m a pretty tame driver so there won’t be
undue stress under the bonnet.</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span style="font-size:
9.0pt; font-family: 'Arial',sans-serif; color: black;
mso-fareast-language: EN-US;">Simon</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span style="font-size:
9.0pt; font-family: 'Arial',sans-serif; color: black;
mso-fareast-language: EN-US;"> </span></p>
<div>
<div style="border: none; border-top: solid #E1E1E1
1.0pt; padding: 3.0pt 0cm 0cm 0cm;">
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><strong><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;" lang="EN-US">From:</span></strong><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;" lang="EN-US"> <a
href="mailto:josef-eckert@t-online.de"
moz-do-not-send="true"
class="moz-txt-link-freetext">josef-eckert@t-online.de</a>
<<a href="mailto:josef-eckert@t-online.de"
moz-do-not-send="true"
class="moz-txt-link-freetext">josef-eckert@t-online.de</a>>
<br>
<strong><span style="font-family:
'Arial',sans-serif;">Sent:</span></strong> 03
May 2023 20:56<br>
<strong><span style="font-family:
'Arial',sans-serif;">To:</span></strong> <a
href="mailto:simon.lachlan@alexarevel.plus.com"
moz-do-not-send="true"
class="moz-txt-link-freetext">simon.lachlan@alexarevel.plus.com</a>;
<a href="mailto:healeys@autox.team.net"
moz-do-not-send="true"
class="moz-txt-link-freetext">healeys@autox.team.net</a><br>
<strong><span style="font-family:
'Arial',sans-serif;">Subject:</span></strong>
AW: [Healeys] Spark plug gap</span></p>
</div>
</div>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span style="font-size:
9.0pt; font-family: 'Arial',sans-serif; color: black;"> </span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">Spark
plugs are designed and tested to be used with the gap
given by the producer of the spark plug.</span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">When
you widen the gap the plug gets hotter as it is
designed for and the electrode can melt or wear very
fast.</span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">Its a
very short win you gain modifying them.</span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">I
never understand why people think they are better
engineers and know better than the designers of the
system they use.</span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;"> </span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;">Josef
</span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;"> </span></p>
<p style="margin: 0px;"><span style="font-size: 10.0pt;
font-family: 'Arial',sans-serif; color: black;"> </span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;"> </span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;"> </span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;">-----Original-Nachricht-----</span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;">Betreff:
[Healeys] Spark plug gap</span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;">Datum:
2023-05-03T21:39:57+0200</span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;">Von:
"Simon Lachlan via Healeys" <<a
href="mailto:healeys@autox.team.net"
moz-do-not-send="true" class="moz-txt-link-freetext">healeys@autox.team.net</a>></span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;">An:
"'Healeys'" <<a
href="mailto:healeys@autox.team.net"
moz-do-not-send="true" class="moz-txt-link-freetext">healeys@autox.team.net</a>></span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;"> </span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;"> </span></p>
<p style="margin: 0px;"><span style="font-size: 9.0pt;
font-family: 'Arial',sans-serif; color: black;"> </span></p>
<div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">I run my MkII
BT7 on NGK BP6ES which were recommended by some of
the wise ones on this list.</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">The car has a
“Sports” coil and a 123Ignition distributor. DW
fast road cam…etc</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">Now, talking of
“recommended”, the rolling road guys told me to
set the plugs at 0.028” and pooh-poohed anything
bigger when I suggested that I’d heard of much
greater gaps with my approximate setup.</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">So, I went with
0.028.</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">The other day,
I decided to experiment and set my spare set at
0.032”. Same NGKs, no mileage on them..decent
plugs. Anyhow, it made a very surprising
difference. All round performance is much
enhanced.</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">Despite it’s
3:54 diff and 28% OD, it was never sluggish on our
local hills. But now it fairly zooms up them.</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">To be frank,
all a bit of a surprise.</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">Not
boasting…just putting that out there in case
anyone else is thinking of going up a few thou…..</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">When I asked
about gaps a few years back, some of the
suggestions were near 0.040”. Surely that a bit
much?</span></p>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span
style="font-size: 9.0pt; font-family:
'Arial',sans-serif; color: black;">Simon</span></p>
</div>
</div>
<p class="MsoNormal" style="mso-margin-top-alt: auto;
mso-margin-bottom-alt: auto;"><span style="font-size:
9.0pt; font-family: 'Arial',sans-serif; color: black;"> </span></p>
</div>
</div>
<p class="MsoNormal"> </p>
</div>
</div>
<br>
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