# theory on how much Kv a spark need to keep firing

Carlos Mobile Technician Puerto Rico Posted   Latest   Edited

Example: a coil produces 30,000 kv and your spark plug is calibrated to 60 thousand of an inch, .060*2.54 =0.1524(30,000*0.1524)=4.1524kv firing

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Glenn Owner/Technician
Texas
Glenn

Hi Carlos, Is this continuing from your previous posting on the subject?

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Funny
Rusty Owner/Technician
Massachusetts
Rusty

It all depends on the environment, lambda, humidity, fuel source, and pressure.

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Brandon Diagnostician
Pennsylvania
Brandon

Carlos, there is more to it than that: The Firing kV demand is determined by the overall secondary circuit’s resistance. With that being said, there are other factors that determine the firing KV demand. -pressure -gap(s) -electrical resistance -cylinder charge composition These three factors are affected by cylinder fill, Air/Fuel ratio, spark plug gap and any other gaps that are…

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Glenn Owner/Technician
Texas
Glenn

Maybe this will help: Ignition Sytem: Types, Parts, Working, Diagram [PDF] (theengineerspost​.​com)

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Gary Owner/Technician
Gary

spark plug is calibrated to 60 thousand of an inch, .060*2.54 =0.1524(30,000*0.1524)=4.1524kv firing You're 'way off on your math, Carlos. Many variables like spark timing, spark plug air gap, running compression, and air/fuel ratio affect spark plug kV at idle speed. In general, a spark plug should be showing in the range of 12kV to 14kV at idle if the engine is properly timed and the…

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Interesting
Glenn Owner/Technician
Texas
Glenn

Hi Gary, I hope you escaped the wildfires up there. I saw it in the news, it had me concerned. Now they have snow complicating the issues after the fact. Anyway, back to the subject: Carlos, you are taking a very loose general approach to your evaluation of the subject. I will give you an example that Ford has had issues with for years along with some other manufacturers. They are running…

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Gary Owner/Technician
Gary

Hello, Glenn. I'm in good shape here except the outside temperature is now 4*F. at 10:00 pm. I was using my snow blower to clear our mail boxes today and caught a big whiff of powdered snow, which just about froze me to death. The latest word is that the Boulder area has three people missing and nearly 1,000 homes burned to the ground. The authorities might take a long time finding those three…

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Thanks
Glenn Owner/Technician
Texas
Glenn

Hi Gary, The most memorable experience I had with altitude differences was years ago when I made regular Motorcycle trips out to Ruidoso New Mexico which is around 12,000 feet above sea level. I left San Antonio at around 600 Feet. I always found at about the halfway point of the trip I would have to pull into a rest stop and tighten my spark plug gaps and richen my main jet in my carb. The…

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