This came up on another thread and I didn't want to hi-jack it, so why did the GM engineers install a reverse polarity HEI coil on some cars? I've always heard it was for simple radio interference, and that the reverse polarity ones reduced radio noise (AM?), but have been leary of that explaination as I would of figured it'd of been cheaper to simply build one type of coil and reduce radio noise in all their cars. That being said, I have multiple times over the years with both my 455 and 231 V6 gone back and forth between the Chevy one and the Buick one, namely dependant on how soon I needed the coil, and usually the reverse polarity one wasn't instock and have never noticed any difference in running or my radio (FM) signal quality. The science guy side of me does not see a functional difference between the two, as it should only reverse the north-south polarity, and it's the collapsing of the magnetic field that induces the spark voltage and that should push the voltage the same way regardless of polarity. Thoughts?
Maybe it has to do with the electron's spin when it enters the primary windings from the other direction.:idea2: Seriously, I can't make a case for a transformer primary winding having the polarity different changing the EMI. Saturation of the inner windings would be the same...unless they are making it a two-pole transformer. I can't imagine why that would be a design feature, because IIRC, there is only one aim for a coil- stepping up the voltage. Two poles would mean one of the two high voltages going somewhere else. All that "somewhere else" is going to the plugs, if it is an efficient coil. IIRC, current flows from the body of the plug to the electrode on Kettering ignition. Guess I'll have to go crack open a book and look again. I haven't read up on this stuff in decades, so I could be remembering it wrong. But from a strongish EM Physics background (5 college semesters), I can't make a case for a difference.
I wouldn't say I have a strong EM background, but did take calculus based physics in college and did spend a few weeks on electricity and magnetics, and I too can't make a case for it. I'm hoping someone sees this and might know of a GM engineering report or something. And it's kind of splitting hairs, but the purpose of the coil isn't so much to step up voltage (that's the function of a transformer), but to induce a significantly high voltage from a magnetic field collapse. I think of 'stepping' as you input voltage A into one end and you get voltage B out the other and more of a constant flow, where the coil requires current to actually stop for it to function as intended.
The ignition coil is a transformer, per se. Maybe "step-up" sounds weird, but the fact that it has a varying (oscillating between approximately 12V and essentially 0V) gozinta and ~40kV gozoutta makes it a step-up transformer. Leaving out the variable battery voltage and charging system variations, this is essentially the case.
I've never seen a difference from one coil to the next other than the wire colors on the big body HEI units. I figured if it was the wrong coil the car wouldn't run right or there would be a fire. Since neither happens I just assume they're interchangeable.
