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Discussion Starter #1 (Edited)
Spark plugs are simply devices that carry a high voltage into the combustion chamber and converts it by jumping a gap into a spark to ignite the air-fuel mixture.

The ideal air-fuel mixture for an internal combustion engine is considered to be 14.7:1. The reason that 14.7:1 is considered the ideal air-fuel mixture is that tests have proven that at this ratio CO’s, HC’s and NOx are at their lowest levels.

At the point of deflagration, and average operating conditions, the maximum temperature of the internal combustion engine flame front hovers around 2,100 to 2,500 deg. C. and wavefront pressures of 50bar occur.

Conditions which create variable figures to those above include;

1/. Sudden temperature changes. Low temperatures of the incoming air-fuel mixture. The plugs are subjected to typical firing conditions that heat the ‘nose’ of the plug in the firing chamber to between 850 to 950 deg. C and suddenly chilled by intake air-fuel mixture.

2/. Sudden pressure changes that are brought to bear by high temperatures of burned gases.

There are others.

The center electrode is now inariably a nickel based alloy with all sorts of traces of other metals added.
The best and hardest to source Racing type spark plugs have iridium-tipped center electrodes with platinum or iridium alloys for ground electrodes.

Ever wondered why the best plugs have a pure copper core? Thermal conductivity. Often overlooked is the fact that the plug is the prime route for heat generated by the ignition of air-fuel leaves the firing chamber.

In higher performance engines the Spark Plug 'gap' is lowered as the compression ratio rises.

The insulation sheath is made of high purity Al2O3 (alumina) that is fired in a kiln at around 1600 deg. C.
It has to be robust to withstand the life it will lead.

The metal shells are formed by either rolling then machined or sawn and machined from a solid hex. bar.
The manufacture of the bit you screw into the head is quite involved, when you look at it, these things are remarkably cheap for the number processes needed to make just one plug.

Many plugs have two, three or four ground electrodes.
The spark occurs at the point of least resistance.
So you do only get ONE spark per ‘firing’.
The real reason for multiple ground electrodes is to reduce the risk of any single ground electrode heating to where pre-ignition can occur.

So much rubbish is written about Heat range that I broach the subject with a little trepidation.
The heat is there to allow the whole thing to self clean, that is it, nothing more than that, wrong heat range and the plug gets dirty (fouls), get it right and you keep firing on all cylinders. :)

Colder plugs have a shorter path to the outside World (called a ‘cold bridge’ when talking about thermal conductivity.)

I bet you would love to know what is the ideal tip temp for burning all that Air/fuel mix, well I’ll tell you it is 725 deg. C. ±25 deg C.

In ‘racing’ engines producing 500+hp heat range is very important indeed.

Edited, cos at this time of night after a hard day at workmy syntax, typing and general formatting skills are appalling.
 

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Nice!

Knowing that one of our 'members' has suffered badly from a plug disintegrating, what could cause this? I guess it would either be a manufacturing fault (unlikely?) or severe detonation presumably?
 

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Discussion Starter #3
Almost all failures of plugs are heat related, the cause is mostly worng Temp. of plug, but faulty ignition timing can do it, but there is a simple check for which has done it...

If only one or two are damaged then timing is your suspect, if nearly all are damaged heat range has done for them.

It ain't a hard and fast rule, but better than 9 out of ten times it will provide the answer.
 

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Do you rate multi-ground electrode plugs Mycroft? I mean, is there actually any real benefit to them? Does excessive heat of the electrode really contribute that greatly to pre-ignition, or is that the most common root cause?
 

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Discussion Starter #5
Sadly yes, glowing plugs are believed to cause more than 70% of the instances of pre-ignition. The remainder is carbon deposits and frankly they are usually causes by incomplete ignition of the Air/fuel mix, the plug is responsible nearly 50% of that remaining 30% so thats 85% of the root cause of pre-ignition is down to those pesky plugs!

Oh I hope you guys have tried to assist you car by cooling the area between the camshfts by removing that plate and blowing some cold air across that part of the head, it is almost as good (on a hot trackday blast) as changing the plug heat by 1 grade!
 

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Cripes, I had no idea it was as high as that, I was under the impression that the bad-boy of pre-ignition was excessive carbon... So potentially you have a major handle on pre-ignition by changing the heat-range of your plugs?
 
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someone else understands plugs

Mycroft,

see you understand plugs, Remove the top cover will help ,
there are vents in the back cover for the cam belt shield this
allows air to be pumped over the coils etc, although if you have
a mis-fire remove the top cover sometimes eradicates it , this is
due normally to the coils over heating when the cover is fitted.
 

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Discussion Starter #8
Abbey (Mark?) I have always had huge sympathy for my plugs they lead a wretched tormented life!

The coils have a torrid time of it too, a point well made.

BTW, the Soarer have packs of 2 coils.ie 3×2 coils, is it the same on the Skyline?
 

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Discussion Starter #9
Danoh, if you have checked everything else then yep, it can reap rewards.
I have cured it on one of my old cars, by adjusting the gap and the heat range slightly.
There are some little variables that you can play with to get the best from your car.

PS, don't confuse 'Pre-ignition' with 'Knock' somewhere on one of the servers at work there are 3 wav. files of an Austin Healey 3000 the first is the car with 'pre-ignition', the second with the same car 'knocking', the final is how it should sound, once heard never forgotten.

Perhaps someone could produce such a thing for this site.
 

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Discussion Starter #10
8 pot has asked the following;


#The spark plug info was interesting but way over my head.#

Bugger! It wasn't meant to, please try again.



#What type of plugs do you recommend at different states of tune, is it worth swapping to fancy plugs even if car is running "stage 1" or 14psi?#

I avoid recommending anything in particular as there are plenty of very (very) competent tuners on here and they are your 'providers'.

I have a very pretentious view of my role here...I just want to 'arm' you with a bit more info than you did if you just fell straight into their arms, this is not to imply that they would serve you wrong, far from it, if the 'feedback' I get is anything to go by, but it is more to get you to be able to articulate want you want and to know what it means to go down that route.
The other is to raise some awareness of the intricacies of design and performance.

That is why your first statement 'hurt'. I have failed yet again, this is not easy to get right, trust me.

Mods, perhaps 8pots other thread is redundant now.
 

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Good info! Cheers

I use the HKS plugs. they are a good all rounder for my engine.
i tried some std NGK copper core but they kept missing on high boost.
then i got some Champion C59 (some kind of racing plug) but they are a bit hard to keep clean with normal driving.

best (for me) were the HKS 5408-S40I (these are for my 220 btw so they might not be right for a skyline)
but i have no info on their heat range or anything really. anyone know about these plugs?

Drew
 

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I have been using NGK coppers on my 240rwkw Gtr and am happy with them. At a pound each i cahnge them every 5k kms and haven't seen one in bad shape yet. 1 range colder(7) and gapped down to 0.8mm seems to do the trick.

Soarer have packs of 2 coils.ie 3×2 coils, is it the same on the Skyline?
Skylines have a coil for each cylinder.
 

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Mycroft,
Sorry no offence intended abouy the thread, I will have to read it again quietly without the wife nagging about playing on this bl**dy computer -she does not understand.
 

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Mycroft,
I can confirm that you only get one spark per firing on multi electrode plugs.

In my recently installed flamer kit I wired it up to a multi electrode plug and when it's switched on you can see the spark jumping between the different electrodes each time but you only get a single spark per firing.

I find the worst conditions for plug 'fouling' tend to be long runs at constant light throttle loads i.e. motorway driving etc where the plugs don't get up to temperature because of the light loads and so progressively get coated with more and more carbon deposits. Always a good excuse to make sure that you leave the motorway early on a run and have a 'spirited' blast to clean your plugs :D

The only plug problems I have had before are with plugs appearing to 'stutter' under hard acceleration at high boost (1.5 bar). I assumed that this was due to a weak spark being 'blown out' by the incoming rush of air and pressure wave when the throttle was suddenly snapped open.

Andy
 

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Discussion Starter #15
The only plug problems I have had before are with plugs appearing to 'stutter' under hard acceleration at high boost (1.5 bar). I assumed that this was due to a weak spark being 'blown out' by the incoming rush of air and pressure wave when the throttle was suddenly snapped open

I have never encountered any circumstances where a spark (providing it is spiteful enough) will not jump the gap.

What actually happens is a subtle form of ionisation around the plug itself, this forces the mixture away from the tip, causing the spark to fire in a zone of little or no Fuel/Air mixture.

Way back in the 80's I designed one of the 'de-ionising' systems for a number of F1 teams, these old Turbo motors suffered this phenomenon to such an extent that at certain revs you could actually destroy the motor!

it usually happens only at high pressure or if there is excessive intake velocity.
 

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Brillaint thread I must say

Mycroft how often do you recommend changing the plugs then?
I have just got some Denso Iridiums from aforementioned tuner and cured a problem I had.
The HKS ones I had in there were there for 15000 mies and this is obviously too much.
I am planning to change every 9k. Is this about right?
Mind you I guess youo change them when they give up but just looking for some safe perameters for other users on here....

Mine is running 1.2 bar btw with a few extras!! So not quite stage one as it were!

NLW
 

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Discussion Starter #17
Mycroft how often do you recommend changing the plugs then?
I don't, the best advice on this comes from the guy who built your engine, he has all the knowledge at his finger tips, that is part of that 'scary' bill, he would have spent a little time thinking about the work he has undertaken for you, he will 'know' how 'hot she will run, he will then fit the plug with the right heat range, people like Mark/Gary/Mario/Tim most likely do this intuitively and frankly that intuition is better than any formula I could devise/envisage.

you can keep removing the plugs after different runs at different paces and circumstances, this is indeed how I taught myself this when younger, ask any 'good' apprentice ENGINEER (not 'fitter') and he will tell you of the hndreds of times he had to remove and inspect the plugs and 'pick-up' tips from the 'Teacher'.

Never resent paying for skill/knowledge, question everything else but not that.

Oh, one other thing...ask...I can't speak for the tuners here but most good tuners never resent or are 'short' with a customer asking such questions...good ENGINEERS like someone who will be in tune with something that has been worked on by them.

Bad'ns want you to break it and spend more.
 

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some interesting stuff, thanks mycroft.

Only problem I have is in certain tuning scenes, I do not trust the engineers.

I trust them to do the things they think about everyday, but ask them to go beyond their routine and they are on just as much unchartered ground as I am.

it depends on their degree of expert.

Lots of people charge a lot of money because they are greedy, not because they are worth, and it takes knowledge like that which you impart to us to know when someone is telling the truth or fobbing you off because they havent got a clue themselves.

eg. I recently had a fuel system made up for a four cylinder car with 8 injectors. The company building the engine wanted all the injectors fuelled sequentially, I insistsed on a parallel system where no injector had more than one other injector between it and the fuel source!

Arguably it doesnt make a lot of difference, but when close to the limit of the engine, I dont want one injector to ever be running elan for any reason I could have avoided just by applying some common sense.
 

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22B,
The thing is that quite a few tuners tend to make something that is relatively simple (in real terms) to sound realtively complex and so the 'baffle with bu!!shit' term springs to mind.

At the end of the day, to improve the power output of an engine requires more air/fuel and the correct timing. When you look at things in these simple terms, things tend to become a lot clearer.

There is a lot of good info out on the web (also lots of bad stuff....) about the basics of engines/suspension/turbos etc etc and it doesn't hurt to get a basic understanding of things before getting work done.

Personally I believe that researching exactly what a change does is a far better way of spending money that just accepting what someone else says.

Andy
 

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well all I can say is that

ABBEY MOTORSPORT have always given it to me straight (well they sometimes go for the cheeky butcher option as well - they like their meat through the back door!!), always answer my stupid questions and always call me back if they can't answer.
I have never felt ripped off, nor robbed, nor have they tried to push sth my way that needs not be.

It has always "tell me what you want from the car" and we will do it...do you want Torque or a quick car from stand still or lots of top end grunt. Never been or felt pushed to do anything other than that.

I agree with and appreciate what Mycroft puts down as he knows his stuff and as you say it does not help to have a good-basic understanding of what is going on in the RB26 as when I open the bonnet it never ceases to amaze me how anyone works on them so the tuners do earn their buck and hats off to them!! Plus it is interesting to get others views on things as for me spark plugs spark, they wear out and need replacing.

But I do leave it to the experts and go on their recommendation as there is so much stuff flying around that it is easy to get confused or pulled in another direction!! With tuning cars for years I have been guilty myself.

But I am very happy with who I am using now, always get a good service and I know I can get the answers I need quickly.

You pays yer way and all that!
NLW
 
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