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Just about to replace my old and oily sparkplugs, to find that a known supplier send me NGK BPR5E with their mantenance kit, should be BPS6ES as per NGK site advice

Has any one come across similar sparkplugs? can i use them? 

1971 TR6 Pi

Thank you

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NGK plugs run hotter the lower the number (some other manufacturers go the other way). So the 5  supplied will be less prone to fouling than the 6.

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The ‘E’ version supplied to you has a V cut into the electrode for a better burn - I used these on my Stag and found them much better than the standard S versions.

as mentioned earlier, the 5 should be better than 6 at preventing fouling.

......Andy

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I've had NGK BUR6ET 3 electrode plugs on my TR6 and GT6 for years. Same heat range as the standard plugs but with 3 electrodes they last for years, tens of thousands of miles. Also seem to give smoother tick over and pick up from low revs.

Nigel

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Good to hear they worked well for you. I have just noticed that you said bpR5e..... the R stands for ‘Resistor’  , I doubt you need that characteristic for your car, I never had a problem with them in the past, but some folk may have a different view. I havn’t used them in my cars for many years though.

they work well for you, drive and enjoy :)

......... Andy

 

 

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Just a dumb question. BB sets the sparkplug gap at 0,25",which I usually do but how important is it to get it right? New Spark plugs the gap is around 0,35" and then I reset for 0,25" the issue is should I leave as original? Biger gap isn't stronger spark then better ignition? 

Thanks 

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Modern cars have some form of electronic ignition , which generally provides higher sparking voltages than the old coil and points system used in the TR-hence the 0.035 gap in the NGK plugs out of the box. 

My BUR6ET plug's gaps are whatever they came as in the box as they can't be changed. They  operate satisfactorily with a Pertronix Igniter and some form of monster coil a previous owner installed in the 1970's.

Edited by Mike C
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In general, a larger spark plug gap is good, allows for a better burn..... but The larger the gap, the greater the strain on the HT system. 

25 thou is the regular position for traditional set with points and std coil.  If you have good quality electronic ignition and high quality/power coil you should be OK with a larger gap, personally, I wouldn’t go over 30 thou, but each to their own. I have run at 35 for a while, but I didn’t notice any improvement in anything so figured I’d reduce stress in the HT circuit and go back to 30.

dealers choice..... trial and error,  go with what works well for you, but don’t be surprised if some of the HT components need to be renewed a little earlier with larger gaps.

......... Andy 

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IIRC you need some sort of resistance in the line be it the leads or cap or plug. If there’s very little resistance the voltage will jump the gap too easily and you get a weaker spark. On the other hand you don’t need resistive leads and resistive plugs as it may put too much load on the coil as it has to build the voltage to a higher level. Not forgetting of course if you have radio the interference will ruin listening to.......(insert here the name of your favoured pop music)

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Errrr- no. Sorry Dave but whoever told you that is a bit muddled.

The resistance is there solely to reduce the rate of current rise and so minimise radio interference. Ideally you would have minimum resistance in order to get the highest spark current.  The resistance will  not make any significant difference to the coil voltage. That is determined by the plug gap. Until the gap breaks down, no current flows so the resistance has no effect on the rate of voltage rise. Once the gap breaks down the resistance just slows the discharge rate a little bit so it makes the spark a bit weaker but allows it to exist a little longer. 

Having a wider plug gap means the coil voltage is higher, which puts more strain on the insulation of the HT winding and of course on the distributor and leads. The spark energy is fixed and is determined by the coil magnetic core and the ampere-turns in the primary so the plug gap determines how that energy is expended. A wide gap will give a higher and hotter spark current but for a shorter time. A narrower gap will give a lower spark current but it will be there for a bit longer. 

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Well that told me! Here I am at gone midnight rummaging around in the loft for my notes... and I can’t find them! 

Excellent piece written by Mr.Pratt and Mr. Witney! 

Covered everything from automotive up to the big radials

But on a point the gap is treated as a resistance, no? So if you had an extra wide gap... resistive plugs and resistive leads. Would one of Mr Lucas’s coils struggle to overcome?

Edited by DaveN
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Sorry Dave - I wasn't trying to shout you down or anything.

The gap is initially an insulator since air is non-conductive. The breakdown voltage of air at ambient temperature and pressure is about 3kV/mm and that rises with pressure so in an engine it will be more. I can't find any data on the effect of fuel mixture on that. A high enough voltage ionises the air which causes it to become conductive and current can flow. There will be some low resistance  of course but negligible in comparison with suppression resistors or leads (otherwise they would never be needed ).

While no current flows, resistance has no effect so the lead and suppressor resistance will not influence the voltage required to break down the gap. It's only once current flows that the suppression resistance comes into effect by limiting the peak current reached.  The coil is essentially a voltage source with the voltage being proportional to the magnitude of the magnetic field, the rate of change of its collapse and the length of the conductor in the field. The coil internal impedance and the external suppression components, if any, will determine the circuit current and voltage once conduction starts.

Yes as you say, an extra-wide gap might make life difficult for a standard coil but mainly because its insulation may not be adequate to withstand the voltages required. It will probably manage to generate sufficient voltage but maybe not for long. Wide gaps really need a purpose-built coil.

It will be interesting to learn what P&W say once you find the notes.

Edited by RobH
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^   a little over my head on first reading and without taking the time to take in what you're saying, but thanks for the explanation.  B)  I'll read it over again until I understand.  

On 8/18/2019 at 10:59 PM, RobH said:

Until the gap breaks down

Does  "the gap breaks down"  mean : the circuit is completed when the electricity jumps across the gap ?   Why not just say "until it sparks"  - Would that colloquialism have a slightly different meaning ?

 

1 hour ago, RobH said:

Wide gaps really need a purpose-built coil.

Is this the purpose of  'sports' coils ?  

I'm not advocating spending to upgrade from a usable standard coil,  but rather if the coil is US, then for normal driving / fast road use or economy cruising, would such a high-voltage big-spark coil make any difference.  ? ie.,  is it worth paying more and to get a performance type ?  

 

On 8/18/2019 at 10:59 PM, RobH said:

A wide gap will give a higher (voltage) and hotter spark current but for a shorter time. A narrower gap will give a lower spark current but it will be there for a bit longer. 

I'm not able to distinguish which is better ..in the practical application of our cars.   I can envisage they'd be benefits of having a (colloquial) "bigger" : higher voltage and hotter spark current,  for a shorter time if the race tuned high-lift cam motor is spinning around at 7000rpm.  But would the bigger spark (higher V & hotter) not be of benefit  ..perhaps through more complete combustion at all times ?  or is a slow burn more efficient at lower (2-4000 rpm) engine speeds ?

Thank you.  Pete. 

 

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Yes Pete - gap breaking down and the spark is essentially the same thing. The spark is just the rapid heating of the ionised air by the current flowing through it.  

As I understand it 'sports coils' are supposed to be able to supply a higher voltage and hence sustain a fatter spark. Whether that translates into better performance is going to depend on a lot of other things. It ought to if it results in better combustion of the air-fuel mixture but if everything else is standard the gain might not be noticeable. If it was a quick fix the original manufacturer would probably have done it.

In answer to the last question I can only offer this which seems to sum it up well. Bear in mind the spark is just the initiation of the burn:

https://performancetrends.com/Definitions/Burn-Rate.htm

Edited by RobH
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"Side gapping" will increase spark length for the same kV.  Works like a lightening conductor in reverse, by focusing the electrical field between the sharp edges of both electrodes. See photo:

http://www.gmtips.com/3rd-degree/dox/tips/ignition/spark.htm

but plug life much reduced !

Modern fine wire plugs with a ca 1mm diam. centre electrode work similarly, but are expensive.

A longer  spark kernel is useful for improving ignition of lean mixture. So no use in a PI TR6.

 But someone will have tried it.

Peter

Edited by Peter Cobbold
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Yes, corners/sharp edges/needle points will concentrate the field and draw a longer spark for the same voltage. Such a feature on both electrodes will improve the separation further. The only disadvantage is that all the spark erosion will take place in this smaller area so you need to fettle and/or replace your plugs more frequently. Not quite win, win, win but almost!

Cheers, Richard

PS: If you get a shock from touching e.g. your car, electrical equipment, radiators, etc. then learn to initially touch them with the palm of your hand, not finger tips as your palm will draw little or no spark.

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I also see that some folk recommend 'indexing' the plug so that the electrode gap is facing the incoming fuel/air mixture.

 

Edited by DaveN
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