Posted by John T on January 28, 2009 at 07:27:39 from (75.65.88.188):
In Reply to: Electronic Ignition posted by Chad504 on January 28, 2009 at 06:04:49:
Chad, Its hard to give a guaranteed "perfect" answer to your questions, but I will give you my best electrical engineers opinion:
QUESTION:
Would I see a performance improvement? Assuming a 3/916 bore with Firecrater pistons and 130# compression?
ANSWER: The firing voltage is a function of 1) The medium (fuel and compression) in which it fires and 2) the plug gap. Therefore, an elec ignition with a high voltage coil will still fire AT THE SAME VOLTAGE the stock ignition would fire. The coils voltage rises ONLY high enough to arc current across the gap AND NO MORE. ALL subject to the stock ignition (say with a 20K max voltage capability) having the ability to fire the plug. Even if a coil is rated at say 40,000 volts, that dont mean it fires the plug gap at that voltage, only high enough to fire the plug, the same as the stock coil would do which (depending on compression) is in the neighborhood of maybe 5,000 to 10,000 volts or so. Its just that the HV coil has the CAPABILITY to rise to 40,000 if necessary versus maybe half that for a stock coil......
SOOOOOOOO will you see any improvement, my best guess is given that compression if the tractor was on a dyno YES there may be some slight HP improvement but I wouldnt expect much UNLESS the compression was wayyyyyyyy higher to the place the stock wouldnt fire at all. Even if theres little HP gain, however, you may still see an improvement in idling and start up (see below for reasaons)
QUESTION
If I was to go this route with the ign and coil, what should I set the plug gap to?
Iffffffff you have BOTH an elec ignition switch PLUS a HV coil I would widen the plug gap to the 0.040 to 0.050 or so range to get a wider fatter hotter higher energy (volts x amps x time) spark discharge. The elec switch gives a faster more positive current switching (no points bounce and ringing) that can handle more coil current (then points can handle) and the HV coil has the ability to rise to a higher voltage necessary to fire across that wider plug gap THEREFORE WITH A elec switch coupled with a HV coil you can discharge more energy (volts x amps x time) across a wider plug gap to initiate combustion. Thats where you may get a better star and idle even though not all that much HP gain butttttt as compression rises remember the HV ignition imrpoves performance muchhhhhhhh more
QUESTION
What about if I just change th ign first, should I open th plug gap?
ANSWER
YES Id widen the plug gap to take advanatge of the extra energy and wider fatter hotter spark if you have BOTH an elec switch and HV coil. Even at the same gap theres still an advantage due to the faster more efficient positive switching versus points switching, but to get all the advantage of an elec switch if you couple it with a high energy HV coil and widen the gap you stand to gain more in improvement.
QUESTION
Also, if I replaced the coil should I change the gap, if keeping the points?
ANSWER
If you replace a stock coil with a HV coil but keep points and widen the gap, she will fire at a higher voltage buttttttttttt you dont gain much. So if you keep the points I wouldnt see much advantage in a wider gap. Again its the combination of a wider gap (need HV coil) PLUS the elec switch (faster more current capable positive switching) that gives you the improvement. If you widen the gap with a stock coil you may be pushing the coils limits a tad versus the higher energy rated HV coil thats designed to work at higher voltages and currents then the4 stock coil....
BOTTOM LINE if you use an elec switch PLUS a HV coil and run a wider gap you gain the advantage the elec switch hss to offer and as compression rises you stand to gain more in HP plus better idle and start up
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