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Jul 21st, 2025 | | | | Joined: Dec 2015 Posts: 43 Wrench Fetcher | | Wrench Fetcher Joined: Dec 2015 Posts: 43 | Does using a 12V coil on a 6V system have any advantages or disadvantages other than a strong blue spark versus a weak orange spark? Thanks! | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | This subject has been beaten to death for years- - - -pretty soon you'll hear some self-styled "engineer" come along and tell you there's no such thing as a 12 volt coil! Just run what the factory installed and forget about all the drama.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Mar 2010 Posts: 10,059 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,059 | Oh, and welcome to Stovebolt, New Guy!
(Sometimes Hotrod's "warm and fuzzy" demeanor is masked by his intensity.)
Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Dec 2015 Posts: 43 Wrench Fetcher | | Wrench Fetcher Joined: Dec 2015 Posts: 43 | Do I need an external resistor when using a 12V battery and 12V coil on the 1960 235 engine in my 1950 3100 with stock 6V system? 52Carl, where in Va. are you? Thanks to all. | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Yes. The "12 Volt" Delco coil is actually designed to operate properly at around 9 to 10 Volts DC. If it's run without a resistor the points will have a very short life due to excessive current flow. During a cold start, the battery voltage will drop to around 9.5 volts, so with the proper resistor bypass circuit in place, the coil will still provide a good spark.
BTW, the myth about the "hot blue spark" that everybody considers to be ideal went away in the mid 1960's when Delco started using TV/Radio suppression cable (TVRS) instead of copper-cored spark plug wires. All that metal-core wire does is cause distributor caps and rotors to burn out prematurely.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Aug 2000 Posts: 1,429 'Bolter | | 'Bolter Joined: Aug 2000 Posts: 1,429 | Just to complicate things, or maybe simplify, there are also 12v coils with an internal resistor.
Dennis
Last edited by DennisM; 02/23/2016 6:41 AM.
40 Chevy 1/2 ton
| | | | | Joined: Mar 2004 Posts: 6,189 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,189 | Denis, The benefit to using an external resistor with the bypass circuit wired correctly is that when the starter is engaged the balast resistor is bypassed putting the full battery voltage to the coil for a better start. If you use an internal resistor coil you loose that feature and the already low voltage while cranking the engine over is made even lower causing hard starts. Mike B  | | | | | Joined: Aug 2000 Posts: 1,429 'Bolter | | 'Bolter Joined: Aug 2000 Posts: 1,429 | I understand what you are saying Mike. It is no issue on my truck though. It cranks fast and starts right up. Maybe because I have the 6-volt starter pushed at 12 volts?
Dennis
40 Chevy 1/2 ton
| | | | | Joined: Dec 2000 Posts: 3,399 Gas Pumper | | Gas Pumper Joined: Dec 2000 Posts: 3,399 | He is asking if the 12 volt coil would benefit him while hes running a 6 volt system. 6 volt systems do not have ballast resistors or bypass circuits. The answer is no, they will run exactly the same. If you are experiencing a weak spark on your 6 volt system, some troubleshooting is in order. All stock ignition systems clear into the 1970's are 6 volt ignition systems. | | | | | Joined: Dec 2015 Posts: 43 Wrench Fetcher | | Wrench Fetcher Joined: Dec 2015 Posts: 43 | Thanks for all the responses. Next question, why did GM go to a 12V coil when all the systems run on 6V? | | | | | Joined: Aug 2000 Posts: 1,429 'Bolter | | 'Bolter Joined: Aug 2000 Posts: 1,429 | 12 volt coil and 12 volt battery doesn't sound like a stock 6 volt system to me. Does that even work without changing the 6-volt generator to 12 volt?
Dennis
40 Chevy 1/2 ton
| | | | | Joined: Dec 2015 Posts: 43 Wrench Fetcher | | Wrench Fetcher Joined: Dec 2015 Posts: 43 | Ignore my last question, I figured it out. Thanks again! | | | | | Joined: Dec 2000 Posts: 3,399 Gas Pumper | | Gas Pumper Joined: Dec 2000 Posts: 3,399 | Shoot!  | | |
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