95REGF150
10+ Year Contributor
- 447
- 242
- Mar 7, 2012
-
Elk Grove,
California
Well it's time to bring back up the stock coil Vs. COP debate. I know that if you read through most threads on here about the subject you will find the general consensus to be that not only are COP setups not an upgrade but that they actually provide worse performance than the OEM coil pack due to the dwell time being fixed in the ECU.
However, I had never seen any actual data on the subject mostly just theory and opinions. Now I personally want COP simply for the more modern look of it in the engine bay over the wires. So I do not care if it performs better than stock. But I would not install something simply for looks that does not perform at least as well as stock.
So while some threads got derailed looking at total spark energy or using CDI boxes I want to focus on the one argument most made as to why a COP setup would be worse than our factory coil pack, the required dwell time. Everyone seems to think that the COP coils will require a longer dwell time because they are designed for use on a sequentially controlled engine and only fire on a cylinders compression stroke rather than both compression and exhaust strokes as in our wasted spark setups. The longer time between firing should allow for a longer dwell time between plug fires and so the coils should be designed to take advantage of that. So when they are used in wasted spark configuration they are now being short charged and not reaching the same total amperage as what we were receiving from the factory coil pack when ran at the same dwell time
At least that was the theory but again no one ever offered any evidence to back it up. So I set out to see if that was really the case. I went to the parts store and bought 4 of the 300M coils and have 2 seperate factory DSM coils in my parts bin. It's pretty easy to measure resistance with your average multimeter but that will not give you enough information to calculate dwell, you also need the inductance which is much harder to measure. Luckily I have a fancy LCR meter at work that can do this easily. Long story short here are the numbers from the two coil setups
OEM DSM Coil Packs
Coil 1 - R=1.03 Ohm L=7.254 mH
Coil 2 - R=1.04 Ohm L=7.471 mH
Coil 3 - R=0.98 Ohm L=6.997 mH
Coil 4 - R=1.03 Ohm L=7.395 mH
Average R=1.02 Ohm L=7.279 mH
300M Coils
Coil 1 - R=0.49 Ohm L=2.441 mH
Coil 2 - R=0.51 Ohm L=2.375 mH
Coil 3 - R=0.52 Ohm L=2.425 mH
Coil 4 - R=0.50 Ohm L=2.467 mH
Average R=0.51 Ohm L=2.427 mH
For the 300M coils we will wire 2 of them in series for each circuit so it will be
Averagex2 R=1.02 Ohm L=4.854 mH
Just by numbers comparison you can see that the 300M coils exactly matched the resistance of the OEM coil pack but the inductance is much lower. So now with this information we can use a formula to calculate the amperage of the coil vs the dwell time. The below charts were all done at 14V for the sake of comparison. Obviously this changes with voltage but all we are interested in here is the comparison between the two.
OEM Coil Pack:
300M Coils x2:
LRC circuits are exponential/asymptotic so since both setups have the same resistance they both approach the same amperage of about 13 Amps. Inductance though plays into the time it takes to get there and that is what we are looking at here. And you can see that actually contrary to everyone's assumptions for the same dwell time they actually end up with MORE current on the 300M coils.
Now this can be a problem if the coil is being ran at an amperage beyond what it can withstand but as many people have been using these coils for a long time I guess its safe to say they can take it. Interestingly enough I found some threads where people were increasing the dwell time by DOUBLE what the factory settings were because they assumed the coils needed it. They didn't report any blown coils so they must be pretty tough. It's just funny because it was completely unecessary.
For reference here is the factory ECU dwell table on a blackbox ECU:
So you can see at 14V the OEM dwell time is around 5.5 mS. So for the OEM coil pack that is just over 7 Amps. On the 300M coils we are seeing over 9 Amps so there is more energy being input to the system. And now I will make the assumption NOT a weaker spark than with the OEM coil pack. Whether that actually equals a stronger spark I can't say.
That's for smarter people than me such as @bastarddsm to explain. I tagged you Kurt because I know you were pretty vocal in some of the COP pro/con threads I read and majorly against them. What's your take on this now that we have some coil values? Am I still missing something?
However, I had never seen any actual data on the subject mostly just theory and opinions. Now I personally want COP simply for the more modern look of it in the engine bay over the wires. So I do not care if it performs better than stock. But I would not install something simply for looks that does not perform at least as well as stock.
So while some threads got derailed looking at total spark energy or using CDI boxes I want to focus on the one argument most made as to why a COP setup would be worse than our factory coil pack, the required dwell time. Everyone seems to think that the COP coils will require a longer dwell time because they are designed for use on a sequentially controlled engine and only fire on a cylinders compression stroke rather than both compression and exhaust strokes as in our wasted spark setups. The longer time between firing should allow for a longer dwell time between plug fires and so the coils should be designed to take advantage of that. So when they are used in wasted spark configuration they are now being short charged and not reaching the same total amperage as what we were receiving from the factory coil pack when ran at the same dwell time
At least that was the theory but again no one ever offered any evidence to back it up. So I set out to see if that was really the case. I went to the parts store and bought 4 of the 300M coils and have 2 seperate factory DSM coils in my parts bin. It's pretty easy to measure resistance with your average multimeter but that will not give you enough information to calculate dwell, you also need the inductance which is much harder to measure. Luckily I have a fancy LCR meter at work that can do this easily. Long story short here are the numbers from the two coil setups
OEM DSM Coil Packs
Coil 1 - R=1.03 Ohm L=7.254 mH
Coil 2 - R=1.04 Ohm L=7.471 mH
Coil 3 - R=0.98 Ohm L=6.997 mH
Coil 4 - R=1.03 Ohm L=7.395 mH
Average R=1.02 Ohm L=7.279 mH
300M Coils
Coil 1 - R=0.49 Ohm L=2.441 mH
Coil 2 - R=0.51 Ohm L=2.375 mH
Coil 3 - R=0.52 Ohm L=2.425 mH
Coil 4 - R=0.50 Ohm L=2.467 mH
Average R=0.51 Ohm L=2.427 mH
For the 300M coils we will wire 2 of them in series for each circuit so it will be
Averagex2 R=1.02 Ohm L=4.854 mH
Just by numbers comparison you can see that the 300M coils exactly matched the resistance of the OEM coil pack but the inductance is much lower. So now with this information we can use a formula to calculate the amperage of the coil vs the dwell time. The below charts were all done at 14V for the sake of comparison. Obviously this changes with voltage but all we are interested in here is the comparison between the two.
OEM Coil Pack:
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300M Coils x2:
You must be logged in to view this image or video.
LRC circuits are exponential/asymptotic so since both setups have the same resistance they both approach the same amperage of about 13 Amps. Inductance though plays into the time it takes to get there and that is what we are looking at here. And you can see that actually contrary to everyone's assumptions for the same dwell time they actually end up with MORE current on the 300M coils.
Now this can be a problem if the coil is being ran at an amperage beyond what it can withstand but as many people have been using these coils for a long time I guess its safe to say they can take it. Interestingly enough I found some threads where people were increasing the dwell time by DOUBLE what the factory settings were because they assumed the coils needed it. They didn't report any blown coils so they must be pretty tough. It's just funny because it was completely unecessary.
For reference here is the factory ECU dwell table on a blackbox ECU:
You must be logged in to view this image or video.
So you can see at 14V the OEM dwell time is around 5.5 mS. So for the OEM coil pack that is just over 7 Amps. On the 300M coils we are seeing over 9 Amps so there is more energy being input to the system. And now I will make the assumption NOT a weaker spark than with the OEM coil pack. Whether that actually equals a stronger spark I can't say.
That's for smarter people than me such as @bastarddsm to explain. I tagged you Kurt because I know you were pretty vocal in some of the COP pro/con threads I read and majorly against them. What's your take on this now that we have some coil values? Am I still missing something?
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