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Old 12-15-2005, 09:10 AM   #12
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Join Date: Feb 2003
Chapter/Region: NESIC
Location: lincoln, ri
2003 GGA MBP
12.9 / 105+


Originally Posted by Element Tuning
I don't know the answer to your question as it pertains to conduction angle. I do know that the older coil packs could take up to 5 ms total dwell without much trouble but the newer coil pack are happier with 3-4 ms of total dwell time. What’s important to remember is that you only need enough dwell time to fully charge a given coil. Adding more time doesn’t necessarily benefit anything and in fact I usually find it can burn out coil packs and cause misfires. Why the misfires? I’m not 100% positive if this is due to overheating or possible spark jumping. I can tell you with conviction that I have not lost power by reducing the dwell times of the STI as I have tested the lower settings on the dyno. We usually make more power because it stops misfiring.

i wasn't sure of the units of the hydra's dwell parameter, and thought for a moment that it was in degrees of crank rotation--that's all i meant by conduction angle. from what you've posted it in straight ms.

that's very intriguing about the longer dwell actually precipitating misfires. one would assume that the opposite would be true, but from what you're saying it seems there's a window of dwell that works best. too long or too short and you get issues.

hmm. something is starting to make some sense here. i have a lot of experience with old antiquated vacuum tube amplifiers which use transformers to couple the high impedance tube circuits to the low impedance speaker loads. a coil is a transformer.

it is absolutely true that once the magnetic circuit of the coil is saturated you will not get any more transmission of energy when the current is interrupted. in fact, depending on the core materials of the coil itself (ie, steel, ferrite, etc), you will likely see a DROP in magnetic permeability once a sufficient level of flux is passing through the core and saturation occurs. a lot of core materials exhibit this tendency. there's a sweet spot in terms of flux vs. permeability where very low and very high flux levels show a dropoff.

the permeability is like a measure of the magnetic conductivity of the material. high permeability means high efficiency in terms of the magnetic portion of the coil. this is a "good thing" and is probably a direction in which the electrical engineers at FHI are going. in other words the newer coil packs are probably more efficient and thus saturate at lower flux levels, and the flux is determined by the # of turns on the coil and the amount of current passing through the coil. the dwell directly sets the amount of current.

so there is some logic behind the "sweet spot" for dwell duration and ultimate spark energy. more current doesn't always = more spark energy because there is an "imperfect" magnetic core material involved that has a varying permeability wrt flux density.


(for the curious, i have a good article on electromagnetics on my website written by an EE friend of mine, henry pasternack.
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