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Spark Plug Gap for Electronic Ignition


Lance
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Hello all,

I'm new to the club so please be gentle.

I have recently bought a GT6 Mk3 with electronic ignition.  

Please could you recommend me the best spark plug gap setting for this?

Many thanks and hope to hear from you.

(sorry it's such a basic question)

 

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Hi Lance,

 a lot depends on which system you have and the general condition of the engine.

Start with 0.030"

Check for ease of starting, smoothness in running and acceleration, MPG.

After a week or so (takes notes) increase by 0.005" run for a week and compare.

If any of it feels not right then close down to 0.025" (standard for contact breaker ignition)

 

Good luck

Roger 

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As above, 25 thou for standard coil and electronic ignition, or open up to around 30 thou with high output 'sports' coil. The bigger the gap, the more risk that something in the HT system will leak or track, so make sure the rotor arm, distributor cap and HT leads are in good condition and don't go beyond 35 thou.

Nigel

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44 minutes ago, Nick Jones said:

You clearly do get a bigger spark as it takes more energy to jump the bigger gap

Actually, no. The amount of energy available is fixed by the coil, so needing more energy to jump the gap means there's less remaining energy available to sustain the spark, so you probably get a weaker one.

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Maybe (and all this is just postulation) the energy available is fixed but the size of the gap sets how long the spark lasts. Small gap - long duration spark, large gap - same energy but all in one go. If this is the case the plug gap might need to be a compromise between how long the spark lasts and its physical length as both of these affect the efficiency of the fuel mix ignition. Any good?

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1 hour ago, Iain T said:

Lance, I have pertronix ignition, flamethrower coil with Bosch WR78 plugs that have 0.9mm (35.4 thou) preset gap and although early days seem to work fine. 

Iain 

I've had exactly the same ignition setup on my GT6 for years and has always worked well, though I replaced the Bosch plugs with NGK BUR6ET a couple of years ago, simply because the old plugs had been there so long.

Nigel

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23 hours ago, Pete Lewis said:

i would say remember you dont get a bigger spark but a larger gap also takes it longer to jump  

pete

Humm, does it?

Does a spark not travel (near enough) at the speed of light, like lightening?  I'd accept it might take longer to initiate the spark, as you need to build up enough potential to actually jump the insulating air gap and a bigger gap means more potential required to reach the tipping point, but once you've hit that tipping point I thought the spark itself would travel as the speed of light.  And the reason moden cars/uprated classic can run a bigger spark is because they have more powerful coild/coil packs that can generate the necessary potential in the available time.

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24 minutes ago, Mjit said:

Does a spark not travel (near enough) at the speed of light, like lightening

No. And neither does lightning (although "lightening" does because it's not the word you want - it's a synonym for illumination).

 

A spark is a chemical reaction that travels at the speed of the electrons being accelerated by the electric field. It's really quite slow.

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40 minutes ago, NonMember said:

No. And neither does lightning (although "lightening" does because it's not the word you want - it's a synonym for illumination).

 

A spark is a chemical reaction that travels at the speed of the electrons being accelerated by the electric field. It's really quite slow.

Quite so. You can photograph a lightning strike/propagation - TRy doing that with day light

What TRavels fastest - Light or Dark

The answer is Dark - because it is always there when the light turns up. (According to Terry Pratchett) 

Roger

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