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Bosch coil


 
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Hp Super C
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PostPosted: Mon Jan 11, 2021 4:14 pm    Post subject: Bosch coil Reply to specific post Reply with quote

Has anyone used a Bosch blue coil on their Farmall? It claims to put out 50,000 volts.
 
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Janicholson
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PostPosted: Mon Jan 11, 2021 9:54 pm    Post subject: Re: Bosch coil Reply to specific post Reply with quote

Coils only putout voltage that fires the plug. 50,000 is lots. 20,000 is more than needed in our world of tractors. If the primary resistence is around 3 to 4 ohms it will not overload the points. If less, it will not be a long lived proposition. Unless there is something very wrong, it does not need voltage it will never reach. Jim
 
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Hp Super C
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PostPosted: Tue Jan 12, 2021 2:11 am    Post subject: Re: Bosch coil Reply to specific post Reply with quote

I checked the specs on a stock coil and it’s 1.5 ohm. Same as the Bosch I found. The reason I’m looking for more spark is I put a 3.25 stepped head piston kit in, 240 head and manifold, and a bigger carb. I’m thinking I can get a little more out of it if I get a hotter coil and open up the plug gap.
 
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Janicholson
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PostPosted: Tue Jan 12, 2021 6:44 am    Post subject: Re: Bosch coil Reply to specific post Reply with quote

If you are pulling with it fantastic. The plugs are probably firing in a 150 or so compression pressure. maybe a bit more you probably know. Gapping a .025 plug to .035 changes the required voltage. Plugs fire as soon as they are presented with enough voltage to jump the gap, and no more. I spent my first 30 years in the automotive industry. and I have seen engines needing 25,000 volts to run at 7500 rpm in cars, and 15,000 in motor cycles.
Looking at diagnostic equipment. So at 7 volts running and charging it would draw about 4.6 amps. if running 14.6 volts charging, it is well into 8 amps without resistor. With resistor of similar ohms, you are back to the 4 amp OK level. A dyno will tell you the answer. Seat of the pants maybe not. If it misses at all when in operation it could help. especially if the original coil had a path to ground before it reaches plug firing voltage. Good luck with it, I like increasing performance until things break. Jim
 
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PostPosted: Tue Jan 12, 2021 10:16 am    Post subject: Re: Bosch coil Reply to specific post Reply with quote

The compression ratio on it is somewhere between 8-8.5:1. The stock 240 had 7.3:1 with flat pistons. The step on the new piston is .2” and the piston is a few thousandths taller from the wrist pin, plus the bigger bore. I’m trying to get it over 40 HP to the PTO.
 
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