ballast resistor jack humphrey the standard ignition ballast resistor spec'd for non fi straight axle and mid year cars gm is shown in the corvette parts book with a nominal ohm rating and indicated as identified with a blue stripe use of ncrs member fred oliva interchange book shows this part as used on corvette and hp chevy passenger cars and only garden variety ballast resistors taken from gm passenger car junkers of the era chevy buick caddy have no evidence of color coding dots stripes have correct original steel band tabs with delco remy emboss and notches as indicated by judging guides either st or nd design style but measure in the ohm range since the ballast resistor sits in series with the coil primary a higher than nominal resistance value will decrease spark voltage does anyone know what tolerance spec gm had on the part has anyone substituted a garden variety passenger car ballast resistor for a corvette rated ignition part before comments please
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Re: Ballast Resistor
re ballast resistor jack humphrey coil is factory stock let's say a every factory spec has a tolerance that's why i asked if anyone knew it while ohm doesn't seem like a lot the resistor is in series with the primary of the coil and coil primary winding are pretty low resistance guys on the order of a few ohms dc impedance so think of the combined series dc impedance as being in the ohm range therefore the shift in voltage drop from the coil primary onto the ballast resistor from a to ohm increase could be significant you could move of the designer's intended energy out of the coil primary and therefore out of the secondary serving the plugs with a too fat ballast resistor the absolute current through the primary is what stores magnetic energy in the coil windings and provides the source for brief high energy voltage output in the secondary windings that's why i asked if anyone knew the factory tolerance spec on the ballast resistor thanks for the attempt to help but i was looking for technical accuracy gm didn't make similar looking parts with unique p n for their health it took an act of congress to create a new part in the drawing system and the corollary purchasing inventory efforts there's probably a bona fide reason why ballast resistors and coils used on corvette hp engines differ from run of the mill passenger cars -
Re: Ballast Resistor
re ballast resistor bill clupper i can't speak for the external resistors but when they were incorporated into the wiring harness we had to hold ohms on a ohm spec i would expect the external to have a similar spec range or about of the target valueComment
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Re: Ballast Resistor
re ballast resistor carl rose hi mr humphrey you bring up a very interesting question it has been a while since college physics but here are a few of my own thoughts is there really a large difference between and ohms as i remember from using my voltmeter shall have to check the calibration there is not i realize that v ir current varies inversely to resitance so mathematically there is difference but practically do you use resistor wires and ac non resistor plugs by the above reasoning how much current is necessary to energize a coil i honestly don't know however i would hypothesize that chevrolet would not use an guage wire if large amounts of current were necessary if you would like an excellent coil that appears stock you might consider the jacobs variable resistance coil about that will change the spark current depending on the load condition mr jacobs also authors an excellent book on theory of ignition systems if you are interested unfortunately the coil is only available in chrome and is slightly longer than stock i blasted mine for better surface adhesion and painted black it is on my ford heresy i know but as i remember it will fit under a ignition shielding and is virtually undetectable just my humble thoughts carlComment
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Re: Ballast Resistor
re ballast resistor jack humphrey thanks for the input your reply of tolerance was the data i was looking for by using another set of part source where used manuals i found the older ohm external resistor was used widely across chevy and other gm passenger cars concours judges look for the older script delco remy emboss in the mounting tab as well as the tiny squared off stamping outdent on the end of the mounting tab neither of these identifying marks are on current service spare replacement components i found my higher than expected resistance readings were caused by aging oxidation on the scrap yard parts i picked up dissassembling the original ballast resistors cleaning with light sand blast where appropriate and re plating key contact points brought them back to within of an ohm of nominal which agrees with your input thanksComment
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