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Restoration & Repair Tips Board

flamethrower coil pertronix for john deere 420

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06-18-2012 16:02:33

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hi i'm thinking i may need a new coil for my john deere 420. i'm debating on whether to get a flamethrower coil or a stock coil? has anyone had experience using these flamethrower coils in tractors? results?

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06-20-2012 14:24:30

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 Re: flamethrower coil pertronix for john deere 420 in reply to nickkalisz, 06-18-2012 16:02:33  
What you must remember is the engine basics. That being with the spark discussion here, all any sparking device is ONLY the trigger to create an explosion of the fuel/air concentration in the combustion chamber. That explosion is what forces the piston down, not the spark. On any spark ignition engine you only need enough spark to lite whatever fuel/air mixture, whether it be gasoline, E-85, methanol and or nitromethane. There any number of variables to trigger the "bomb". Controlled burn of the mixture is where power is made versus the coil as such, 1 of many future discussions, Dale

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06-18-2012 22:30:21

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 Re: flamethrower coil pertronix for john deere 420 in reply to nickkalisz, 06-18-2012 16:02:33  
Non of these coils even with EI will improve the power output of the engine. What the flame thrower and EI will by you is to provide a good spark when the plugs have deteriorated and the gaps opens up. The EI frees you from replacing and adjusting points.

I am a big proponent of EI and I used to be a proponent of Pertronix EI but I had some reliability issues with the Pertronix unit on my TO-30 and I"ve gone back to conventional points. I think Pertronix has some QC issues with their module and the result is a lack of reliability (two failures within three months after 5 years of no problems) which to me is the only advantage of EI.

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John T

06-18-2012 16:33:42

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 Heres the real deal in reply to nickkalisz, 06-18-2012 16:02:33  
1) If you continue the use of mechanical points, which its not best to switch much over 4 amps of current, the Flame Thrower or Accell Or Super Coil or Super HV Coil or the Billy Bob Special Super Super Coil, or the factory stock coil IF ALL ELSE REMAINS THE SAME (compression and fuel) WILL NOT YIELD MUCH IF ANY GREATLY MEASURABLE DIFFERENCE IN PERFORMANCE AND THE FIRING VOLTAGE WILL REMAIN THE SAME REGARDLESS WHICH COIL IS USED !!!!!!!!!!!!!!!!

2) If you use any combination of coil plus ballast in the primary ignition circuit that has a total resistance a lot under 3 ohms (for a 12 volt system or half that if a 6 volt) and you still use points, THE POINTS WILL BURN UP SOONER AND IN TIME THE PERFORMANCE WILL BE DRASTICALLY REDUCED !!!!!!!!!!!!

3) Iffffffffffff the flame thrower has a primary resistance in the neighborhood similar to the stock coil i.e. around 2.5 to under 4 ohms (for a 12 volt or half that if 6 volt) you can use it unballasted in place of the stock coil and the points will last about the same and performance will be about the same NOT ANY PROBLEM

HOWEVER if you combine a high energy coil with an elec switch that has the capacity to switch the coils current IT IS POSSIBLE TO DISCHARGE A SPARK GAP WITH HIGHER ENERGY THEN THE STOCK SYSTEM AND "POSSIBLY" GET BETTER PERFORMANCE

BOTTOM LINE Be careful of HV after market coils use on a stock points system as if the point current is greatly increased they will burn and carbon sooner and performance will be poor pretty quick I.E. CHECK THE COILS LV PRIMARY RESISTANCE needs to be around 1.25 to uncer 2 ohms for a 6 volt system (or if on a 12 volt with an added ballast) or 2.5 to 4 on a 12 volt system......

Those high energy coils are more for elec switch use that can handle their higher current, they can still be used with points if their resistance matches the stock coils so the points dont burn up prematurely but if they cause the points curfrent to rise dramatically the poinst will burn caRBON AND performance will go real bad real quick

John T At Lake Meade and Hoover Dam NevaDA/Arizona today

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Dean Olson

06-18-2012 16:22:59

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 Re: flamethrower coil pertronix for john deere 420 in reply to nickkalisz, 06-18-2012 16:02:33  
I had one on a Farmall Super C and couldn't tell any difference in performance. It lasted about a year and a half and failed. I put a new cheap stock type Napa coil back on. Been fine ever since.

I seem to remember that a given engine only needs "X" amount of voltage to start the air/fuel mixture burning and that anything beyond that is wasted.

I think that stock for your 420 will be fine.

Unless of course you have a blower,turbo, and are dumping huge quantities of fuel in it:)

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John T

06-18-2012 16:49:19

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 Re: flamethrower coil pertronix for john deere 420 in reply to Dean Olson, 06-18-2012 16:22:59  
Dean, youre pretty much on track,,the voltage necessary to arc jump current across a given gap is a function of the gap thickness and the medium (fuel and compression) in which it fires. When the coil fires its voltage ramps up b ut only until its high enough to fire the plug and no higher and in a stoc k engine that may be 5K to 15K volts or so depending on gap and c ompression. The HV coils advertised to fire at 40,000 volts =dont mean they fire at that voltage, if only 10,000 fires ther plug thats all they go to but if you widen the gap and/or raise the compression 30 to 40K may be necessary

John T

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36 coupe

06-19-2012 16:01:47

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 Re: flamethrower coil pertronix for john deere 420 in reply to John T, 06-18-2012 16:49:19  
40 K in a 9n distrubutor cap would be a disaster.The rotor would break down an arc to the distrutor shaft.I think all cylinders would have spark at the same time.The ignition wires would arc over.I have worked with 25 to 30K in color Tvs for 40 years.25 K can jump a 1 inch gap in open air.Just take a look at A gm HEI cap or the cap in a 96 and later Ford.

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John T

06-19-2012 19:08:59

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 Re: flamethrower coil pertronix for john deere 420 in reply to 36 coupe, 06-19-2012 16:01:47  
EXACTLY, thats why most of the hype and sales adds are full of it lol Typical firing voltages are wayyyyyyy less then 40 K

John T

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