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Old 10-31-2002, 11:46 AM   #1
Midwayman
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Talking What is Dwell?

Playing with my Link under ignition settings I have two settings for dwell. 4ms and 5.5ms. Im guessing this is the time the spark plugs stay on with each ignition event? Anyone know exactly what dwell is, and probably more importantly how much you need?

I know it changes the sound of my engine dramatically.
It seems to have more knock resistance with less dwell
But seems to make less power with less dwell.
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Old 10-31-2002, 12:42 PM   #2
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I believe it's how long it takes for it to fire from time of sending the signal.

Reason it has more knock resistence, is that you're in effect running more retarded timing when you lower it (it signals later thinking it'll be on time and actually fires later).
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Old 10-31-2002, 12:50 PM   #3
HndaTch627
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dwell is the time that the coil is charging, before the ground is shut off and the spark is induced.

jeremy
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Old 10-31-2002, 12:52 PM   #4
Midwayman
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http://ourworld.compuserve.com/homep...ition/CDI.HTML

"Dwell time refers to the time the distributor points are closed. The dwell angle was the amount of rotation of the crankshaft that corresponded to the points being closed. This affects the charge time of the coil and hence spark length. Dwell was important then because at higher RPM the dwell time (points are closed to charge the coil) was not enough to fully charge the induction coil. That meant less voltage spark at higher RPM (...BAD). There was also the problem of how fast a point could open and close without "floating" (a problem you have with valves also). There was a real balance between dwell time at high RPM, how much voltage you needed for high RPM spark, how much voltage you could actually push thru a point without burning it up, and then what would happen at low rpm (long dwell times) when all that voltage was just heating up the coils.

In newer CDI systems this term is near meaningless for several reasons. Solid state transistors control the discharge pulses electronically with near instantaneous timings. So the dwell times can be finely controlled to achieve the best coil / spark outputs for any given RPM. Transistors can handle a LARGE amounts of voltage/current (compared to points). And, newer generation coils are extremely fast. Their coil pulse "voltage rise time" to the plug is VERY fast at around 6 microseconds). So charge / discharge times are not a huge factor (unless racing). Newer racing ignitions (like MSD) are NOT producing bigger sparks with long durations but in fact getting more effecient burn by producing very controlled multiple short duration sparks to the plug."


So my reading is that dwell is esentially the charge time of your coil pack. Big dwell, bigger spark. Tooo much dwell and the coil might blow. Sound right?
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Old 10-31-2002, 02:39 PM   #5
Midwayman
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Another interesting article...
http://www.tonyfoale.com/Articles/Ignition/Ignition.htm

Anyhow I think I have a hang on dwell.

Dwell is the charge time for the coil pack. Coil packs take a specific time to reach maxinum charge. Any further dwell time only create unnessacary heat. EG a coil may be come fully charged after 5ms charging for 7ms only adds heat.
Charging less than the maxinum results in weaker spark and poorer ignition formance.

fwiw at 7k rpm you have 8.7ms for each revolution. RS coil packs fire every other revolution. so 17.4ms between firings at 7krpm. you need about 1ms dead time. So a maxinum dwell of 16.4ms.
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