[Healeys] Spark plug gap
Bob Spidell
bspidell at comcast.net
Fri May 5 18:25:22 MDT 2023
re: "... all this fiddling with the spark plug gap to account for the
engine’s particulars must be a fool’s errand, and cannot possibly work!! "
It works if your car runs smoothly. If you run a little toward the lean
side--which Healeys don't like--a performance coil and a little more gap
may help give a little smoother running engine. Running very rich, to
the point you get black soot out of the exhaust is not advisable for a
number of reasons. So, set your mixture as you like and set your gap at
book 'spec,' or a little larger if you like. A carburetted engine isn't
likely to run at stoichiometric, except possibly under specific
conditions and, probably, purely accidentally. Running very lean
increases NOx emissions--why some engines have EGR valves (boo
hiss)--and running rich will kill a catalytic converter before someone
even gets a chance to steal it.
Piston aircraft with well-designed fuel injection systems--typically
Continentals--tuned injectors and multi-cylinder CHT/EGT meters can run
'lean of peak' for economy/endurance. Running at peak, i.e.
stoichiometric, is inadvisable because it produces the hottest
combustion temperatures and will cook these glorified lawnmower engines.
Richard M. probably has dyno numbers that show the effect of mixture vs.
plug gap.
bs
On 5/5/2023 4:05 PM, alfuller194 at gmail.com wrote:
>
> Bob – I’m afraid you have me confused…
>
> You indicated “…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 Josef tells us that “ …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. …”
>
> SO – If one can use an instrument and get a perfectly stoichiometric
> air/fuel ratio and it doesn’t give best results [Worse at altitude or
> in the summer driving season!] – then surely all this fiddling with
> the spark plug gap to account for the engine’s particulars must be a
> fool’s errand, and cannot possibly work!!
>
> P.S.: And whatever you – do NOT adjust the timing to try to make the
> car run its best.
>
> ----------------
>
> All the best,
>
> Al Fuller
>
> *From:* Healeys <healeys-bounces at autox.team.net> *On Behalf Of *Bob
> Spidell
> *Sent:* Thursday, May 4, 2023 7:56 AM
> *To:* healeys at autox.team.net
> *Subject:* Re: [Healeys] Spark plug gap
>
> 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.
>
> 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 ...
>
> 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 /slight/ 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.
>
> 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).
>
> OK, caffeine rush is fading. Ciao.
>
> Bob
>
> * 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.
>
>
> On 5/4/2023 4:43 AM, josef-eckert--- via Healeys wrote:
>
> Sorry, I am out here. This guy wants to play till the engine is shot.
>
> -----Original-Nachricht-----
>
> Betreff: RE: [Healeys] Spark plug gap
>
> Datum: 2023-05-04T12:45:37+0200
>
> Von: "simon.lachlan at alexarevel.plus.com"
> <mailto:simon.lachlan at alexarevel.plus.com>
> <simon.lachlan at alexarevel.plus.com>
> <mailto:simon.lachlan at alexarevel.plus.com>
>
> An: "josef-eckert at t-online.de" <mailto:josef-eckert at t-online.de>
> <josef-eckert at t-online.de> <mailto:josef-eckert at t-online.de>
>
> 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.
>
> Someone mentioned that he used “Iridium” plugs from NGK. I googled
> them….horribly expensive. Can they be worth it in our old cars?
>
> Simon
>
> *From:*josef-eckert at t-online.de <josef-eckert at t-online.de>
> <mailto:josef-eckert at t-online.de>
> *Sent:* 04 May 2023 07:06
> *To:* simon.lachlan at alexarevel.plus.com; Healey, Forum
> <healeys at autox.team.net> <mailto:healeys at autox.team.net>
> *Subject:* AW: [Healeys] Spark plug gap
>
> 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.
>
> 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.
>
> 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.
>
> 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.
>
> Josef
>
> -----Original-Nachricht-----
>
> Betreff: RE: [Healeys] Spark plug gap
>
> Datum: 2023-05-04T00:06:58+0200
>
> Von: "simon.lachlan at alexarevel.plus.com"
> <simon.lachlan at alexarevel.plus.com>
>
> An: "josef-eckert at t-online.de" <josef-eckert at t-online.de>
>
> You may be right. Not sure.
>
> 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.
>
> 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.
>
> Anyhow, I’ll keep an eye on them. I’m a pretty tame driver so
> there won’t be undue stress under the bonnet.
>
> Simon
>
> *From:*josef-eckert at t-online.de <josef-eckert at t-online.de>
> *Sent:* 03 May 2023 20:56
> *To:* simon.lachlan at alexarevel.plus.com; healeys at autox.team.net
> *Subject:* AW: [Healeys] Spark plug gap
>
> Spark plugs are designed and tested to be used with the gap given
> by the producer of the spark plug.
>
> When you widen the gap the plug gets hotter as it is designed for
> and the electrode can melt or wear very fast.
>
> Its a very short win you gain modifying them.
>
> I never understand why people think they are better engineers and
> know better than the designers of the system they use.
>
> Josef
>
> -----Original-Nachricht-----
>
> Betreff: [Healeys] Spark plug gap
>
> Datum: 2023-05-03T21:39:57+0200
>
> Von: "Simon Lachlan via Healeys" <healeys at autox.team.net>
>
> An: "'Healeys'" <healeys at autox.team.net>
>
> I run my MkII BT7 on NGK BP6ES which were recommended by some of
> the wise ones on this list.
>
> The car has a “Sports” coil and a 123Ignition distributor. DW fast
> road cam…etc
>
> 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.
>
> So, I went with 0.028.
>
> 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.
>
> Despite it’s 3:54 diff and 28% OD, it was never sluggish on our
> local hills. But now it fairly zooms up them.
>
> To be frank, all a bit of a surprise.
>
> Not boasting…just putting that out there in case anyone else is
> thinking of going up a few thou…..
>
> When I asked about gaps a few years back, some of the suggestions
> were near 0.040”. Surely that a bit much?
>
> Simon
>
>
>
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