Researching coil dwell and spark duration. This subject, specifically coils, is queried and commented on on most forums when older motorcycles are involved.
The engine tuning software, Tuner Studio (TS), permits the user to input settings for coil dwell and spark duration.
Coil dwell is simple, amount of time needed to bring the coil to the optimum coil charge for the engine in question. In a distributor type system, this is the time between each corner of the distributor shaft when the points are opened allowing the coil charge to go through the spark plug to ground, igniting the air-fuel mixture in the engine cylinder. The spark duration is the time the points are open, extremely quick. The coil and spark duration are calibrated for a specific engine.
I have commented on coil changes in that a coil will provide adequate engine operation, but the coil internal wiring must be the same. Using a coil that is not exactly the same does impact on engine power and fuel economy.
Changing a distributor system to an electronic ignition module is a good upgrade but you must ensure that the coil dwell period and spark duration is maintained to continue having optimum engine power and fuel economy.
Along came EFI where the OEM tuned the engine to achieve the same aim as with a distributor type ignition system. The OEM, very guarded in how it did the work, could after installation, adjust the coil dwell and spark duration if required. The OEM did not provide the owner with the tool(s) to do this, but most of us just want to start the engine, put the vehicle in "D" for ditch and go.
Bring on aftermarket/replacement ECUs, and carburetor to EFI conversions. The owner now wants to control the engine's destiny.
Aftermarket/replacement ECUs generally have engine tuning software that allows the owner/tuner to calibrate the engine tune, and two of these parameters are coil dwell and spark duration.
There are a lot of coils on the market and some will have the data required such as dwell time, but a lot will not. A caution regarding this is that all coils regardless of what the coil is purported to do and what it is for are not always created equal. Internal wiring sizes, primary/secondary, can be smaller or larger, changing the coil charge/discharge characteristics. The time required to discharge the coil, spark duration, may or may not be known.
The coil discharge through the spark plug regardless of spark duration must be sufficient to provide good air-fuel mixture burn. A coil that does not fully charge will not provide a long enough or hot enough spark to completely ignite the air-fuel mixture, or be able to bridge the spark plug gap. Too much coil charge - dwell time too long, and the coil may not discharge fully, and be too much and exceed the spark plug electrode gap. Too much coil charge can overheat the coil and cause it to fail.
The issue with a coil is the primary coil current. The coil resistance remains the same as does the voltage. The coil primary current is dependent system voltage, resistance constant.
An example I found on-line.for a specific coil indicated that for a coil primary circuit current of 2 amps, the spark generated only bridged a spark plug gap of 5 mm. For the same coil, a primary circuit current of 7 amps resulted in the spark bridging a spark plug gap of 22 mm. To achieve this variation of current in this specific coil, the coil dwell time had to be increased by over 3 ms indicating how critical correct coil dwell time is.
For the specific coil example, spark duration was also investigated. Spark duration for a primary coil circuit of 2 amps indicated that the spark duration was only 0.56 ms, whereas a primary coil circuit of 7 amps was 1.4 ms.
The coil driver is part of this equation. Two types available; "closed loop" electronic ignition module - no ECU dwell map, or a mapped dwell - ECU controlled.
The "closed loop" modules monitor the coil current and adjust the dwell time to ensure the target current level is always achieved, something like an alternator monitoring the electrical system voltage. These modules generally use 7 amps as the set point to be maintained.
ECU controlled modules use the settings in the engine tune to control the coil dwell (charge time).
I have thought about this regarding the ability to input a setting for coil dwell and spark duration. From my layman's consideration, setting the spark duration at say 2 ms, and not having enough dwell time to have the correct corresponding coil charge, is not advantageous. The coil dwell time must be adequate enough to provide a discharge spark for the required spark duration.
This can be achieved by bench testing, requiring instrumentation and well thought out procedure, or by experimentation on engine. Most of us will try the experimentation route.
I have investigated a new timing light. The options are quite extensive with varying prices; however, I did find one timing light that does more than indicate engine ignition timing. The Snap-On Ultra Light EETL500 - not inexpensive. It can measure engine RPM, ignition advance and dwell, measures burn voltage and burn time, checks current battery state, measure and display kV readings (view individual cylinder firing voltage, perform snap throttle and coil stress tests), and diagnosis faulty ignition wires/plugs/modules/coils. Will not; however, make lunch.
This timing light has a focus on the hot rod and car enthusiast group.
Just a few thoughts on how our engines operate. Cheers
The engine tuning software, Tuner Studio (TS), permits the user to input settings for coil dwell and spark duration.
Coil dwell is simple, amount of time needed to bring the coil to the optimum coil charge for the engine in question. In a distributor type system, this is the time between each corner of the distributor shaft when the points are opened allowing the coil charge to go through the spark plug to ground, igniting the air-fuel mixture in the engine cylinder. The spark duration is the time the points are open, extremely quick. The coil and spark duration are calibrated for a specific engine.
I have commented on coil changes in that a coil will provide adequate engine operation, but the coil internal wiring must be the same. Using a coil that is not exactly the same does impact on engine power and fuel economy.
Changing a distributor system to an electronic ignition module is a good upgrade but you must ensure that the coil dwell period and spark duration is maintained to continue having optimum engine power and fuel economy.
Along came EFI where the OEM tuned the engine to achieve the same aim as with a distributor type ignition system. The OEM, very guarded in how it did the work, could after installation, adjust the coil dwell and spark duration if required. The OEM did not provide the owner with the tool(s) to do this, but most of us just want to start the engine, put the vehicle in "D" for ditch and go.
Bring on aftermarket/replacement ECUs, and carburetor to EFI conversions. The owner now wants to control the engine's destiny.
Aftermarket/replacement ECUs generally have engine tuning software that allows the owner/tuner to calibrate the engine tune, and two of these parameters are coil dwell and spark duration.
There are a lot of coils on the market and some will have the data required such as dwell time, but a lot will not. A caution regarding this is that all coils regardless of what the coil is purported to do and what it is for are not always created equal. Internal wiring sizes, primary/secondary, can be smaller or larger, changing the coil charge/discharge characteristics. The time required to discharge the coil, spark duration, may or may not be known.
The coil discharge through the spark plug regardless of spark duration must be sufficient to provide good air-fuel mixture burn. A coil that does not fully charge will not provide a long enough or hot enough spark to completely ignite the air-fuel mixture, or be able to bridge the spark plug gap. Too much coil charge - dwell time too long, and the coil may not discharge fully, and be too much and exceed the spark plug electrode gap. Too much coil charge can overheat the coil and cause it to fail.
The issue with a coil is the primary coil current. The coil resistance remains the same as does the voltage. The coil primary current is dependent system voltage, resistance constant.
An example I found on-line.for a specific coil indicated that for a coil primary circuit current of 2 amps, the spark generated only bridged a spark plug gap of 5 mm. For the same coil, a primary circuit current of 7 amps resulted in the spark bridging a spark plug gap of 22 mm. To achieve this variation of current in this specific coil, the coil dwell time had to be increased by over 3 ms indicating how critical correct coil dwell time is.
For the specific coil example, spark duration was also investigated. Spark duration for a primary coil circuit of 2 amps indicated that the spark duration was only 0.56 ms, whereas a primary coil circuit of 7 amps was 1.4 ms.
The coil driver is part of this equation. Two types available; "closed loop" electronic ignition module - no ECU dwell map, or a mapped dwell - ECU controlled.
The "closed loop" modules monitor the coil current and adjust the dwell time to ensure the target current level is always achieved, something like an alternator monitoring the electrical system voltage. These modules generally use 7 amps as the set point to be maintained.
ECU controlled modules use the settings in the engine tune to control the coil dwell (charge time).
I have thought about this regarding the ability to input a setting for coil dwell and spark duration. From my layman's consideration, setting the spark duration at say 2 ms, and not having enough dwell time to have the correct corresponding coil charge, is not advantageous. The coil dwell time must be adequate enough to provide a discharge spark for the required spark duration.
This can be achieved by bench testing, requiring instrumentation and well thought out procedure, or by experimentation on engine. Most of us will try the experimentation route.
I have investigated a new timing light. The options are quite extensive with varying prices; however, I did find one timing light that does more than indicate engine ignition timing. The Snap-On Ultra Light EETL500 - not inexpensive. It can measure engine RPM, ignition advance and dwell, measures burn voltage and burn time, checks current battery state, measure and display kV readings (view individual cylinder firing voltage, perform snap throttle and coil stress tests), and diagnosis faulty ignition wires/plugs/modules/coils. Will not; however, make lunch.
This timing light has a focus on the hot rod and car enthusiast group.
Just a few thoughts on how our engines operate. Cheers
