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the coil thread

Old 05-15-13, 11:44 AM
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the coil thread

i don't know much about ignition, however there have been some coils testing going on and ts time to share the results.

first up is this https://www.rx7club.com/haltech-foru.../#post11386667

like the post says, we assume more energy is better, but have no idea about peak voltage vs spark time.

then i asked to have the FC, Rx8 and LS2 truck tested, here they are at max power




and then we retested at "factory" dwell times

finished test at 2 ms

FC
2 ms charge = 240 mV peak, 0.8 ms duration
4.5 ms charge = 510 mV peak, 1.3 ms duration

LS2
2 ms charge = 630 mV peak, 0.25 ms duration
6 ms charge = 1300 mV peak, 0.5 ms duration

RX-8
2 ms charge = 630 mV peak, 0.4 ms duration
4 ms charge = 840 mV peak, 0.5 ms duration

so under 3ms charge, rx-8 coil is the best of the three
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conclusions? dwell time is important!
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Old 05-15-13, 12:17 PM
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actually hypothesis #2 is that the more RPM you run the shorter discharge time you want. you want to spend the most time burning the fuel and not sparking the plug.

notice its a hypothesis, not a fact...
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Old 05-15-13, 06:56 PM
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here is a shot of the mercury IGN-1A



these plots were made by discharging the coil into 800V of zener diodes and a 10 ohm resistor in series, voltage measured across the resistor
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Old 05-19-13, 03:58 PM
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Originally Posted by gxl90rx7 View Post
here is a shot of the mercury IGN-1A



these plots were made by discharging the coil into 800V of zener diodes and a 10 ohm resistor in series, voltage measured across the resistor
I don't know how to read these charts. How do these coils performance relate to the 3 tested above? Also could anyone also test the Ls1 coils as done so above?
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Old 05-29-13, 08:31 AM
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Originally Posted by t-von View Post
I don't know how to read these charts. How do these coils performance relate to the 3 tested above? Also could anyone also test the Ls1 coils as done so above?
the peak voltage shows how "hot" a coil is.. the hotter the coil, the easier it will be able to bridge a spark plug gap in adverse conditions (high boost, rich mixtures, using water injection, etc).

but there is also the factor of spark duration, which is how long the coil takes to fully discharge, or how long the spark plug is lit. longer discharge means the more energy storage capability of the coil. a hot output is no good if it does not last long enough to fully ignite the mixture, especially in the long combustion chamber of a rotary

the charts above show the LS2 having the hottest output, but shortest duration. the FC coil has the lowest output, but longest duration. The IGN seems to be a good compromise between both. The rx-8 coil seems to work best with low charge times (high rpm)

In general, the physically larger the coil, the more coil inductance, which means longer duration. its no surprise the FC coils are the largest of these

i will add some more plots of LS1, as well as what happens when you overcharge them (and if they auto discharge)
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Old 05-29-13, 07:54 PM
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Originally Posted by gxl90rx7 View Post
the peak voltage shows how "hot" a coil is.. the hotter the coil, the easier it will be able to bridge a spark plug gap in adverse conditions (high boost, rich mixtures, using water injection, etc).

but there is also the factor of spark duration, which is how long the coil takes to fully discharge, or how long the spark plug is lit. longer discharge means the more energy storage capability of the coil. a hot output is no good if it does not last long enough to fully ignite the mixture, especially in the long combustion chamber of a rotary

the charts above show the LS2 having the hottest output, but shortest duration. the FC coil has the lowest output, but longest duration. The IGN seems to be a good compromise between both. The rx-8 coil seems to work best with low charge times (high rpm)

In general, the physically larger the coil, the more coil inductance, which means longer duration. its no surprise the FC coils are the largest of these

i will add some more plots of LS1, as well as what happens when you overcharge them (and if they auto discharge)

Wholy sh*t I totally understood that. Thx! I have a set of Fc coils for my 20b that I tried out at one point and noticed a small drop in power over the Ls1's. Now I wonder how well fc coils would perform in this test with an amp? Could they maintain the same duration with a hotter spark? I'm getting ready to eliminate my power steering and can build a nice bracket to hold those larger coils in the old power steering pump location.

So in general, Na rotarys don't really need a really hot spark as they run leaner but all rotarys need longer duration due to cumbustion chamber size to get a more complete burn?
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Old 05-30-13, 04:57 AM
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I'm still confused at how you keep saying the LS truck coil (assuming D585 truck coil?) is hotter than everything else. Your charts and labeling clearly show the IGN-1A achieving 7 divisions of voltage at 3.5ms charge and the LS truck coils achieving the same 7 divisions with 6 ms charge.

Also, the LS1 coil is not the one to check for auto discharge.
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Old 05-30-13, 08:55 AM
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the LS2 does have the highest voltage, its weird that only that coil causes my misfires. The IGN1A graph is just zoomed in more.. In the posts above, look at the volts/div for the blue lines, the LS2 pic is 200mV/div and IGN1A is 100mV/div. Counting the divisions, the LS2 coil tops out at almost 1.4V, while the IGN1A at 3.5ms tops out at 0.6 V

i was not able to get an LS1 coil yet, none in stock locally. i did try to overcharge the LS2, but i could not get it to auto-discharge. I ran it at 15ms charge for 5 minutes and it just got really hot, but no auto-discharge happened. this guy was able to get one to auto-discharge..

http://forums.hybridz.org/topic/5464...-2#entry707110

maybe it depends on the particular brand?


Here are some more shots of the IGN-1A at higher charge times, it is beastly at 10ms lol



for ***** and giggles I also ran the FD coil last night, here it is at 4ms:



not really impressive, slightly more voltage than the FC coil , but about half the duration, which is no surprise since it is smaller in physical size, so less inductance


i also got my hands on an MSD 6A ignition controller P/N 2600.. it uses a CDI circuit to multiple-strike a coil of your choice, this is with the FD coil


each restrike is 1.2ms apart, and each peaks at 2V with duration of only 150 us (0.015 ms), but it restrikes 8 times up to 3000rpm, where it gradually backs off to to 4 restrikes, and down to 2 restrikes at 6000 rpm. If you ran this on the factory wastespark setup, divide all those rpms by 2, so at 3000rpm it would be down to only 2 restrikes
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Old 05-30-13, 12:45 PM
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/\ nice way to illustrate a point i have been making for years about the MSD/wastespark scenario dropping down to minimal numbers of strike very early and before peak TQ for most of us

it sums up as while those with MSD /wastespark overtake the HEI / wastespark guys upwards from 8500 rpm .. they might not be better from 3000-8000 where most engines are at peak TQ

it also shows how a late 80's mazda heavily backed the longest duration HEI spark with ( only ) the necessary voltage to jump the large SD plug gaps
perhaps themselves at that point conceding that the spark duration is the single most influential / desirable quality of spark for a full burn once a certain threshold voltage has been achieved
( ie.. no further gains and maybe only issues can be had from a further higher voltage strike in the same peak pressure conditions )
keep in mind higher voltages tend to force arc paths easier and may have been seen as a service liability by the factory and thus duration was sort as best path for best burn for street type conditions

its info like this that is turning people back to HEI and hybrid/HEI ignition systems .. more so when many now understand the sequential ignition HEI CNP/COP ECU setups are not limited in dwell until silly rpms and offer more potential over much more of the rev range under normalish mixtures than the CDI can
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Old 05-30-13, 04:25 PM
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So what I am trying to understand is that with my relatively high revving 13B 1/2 bridge (8500-9000) are the stock FC coils inhibiting my higher rpm range? I always felt that the MSD wasn't a help, but should I convert to RX8 coils as they are designed for the rpm ranges I am in? I know these are simplistic questions, but I am looking for a broad brush type of answer.

Eric
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Old 05-30-13, 04:26 PM
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This is great info. Kudos to you for taking the time to do the tests!

My subjective $.02...

- From what I've gathered on the D585 auto-discharge, it's pretty random. There are a ton of these things being made by aftermarket companies and, I'm guessing, more than one OE supplier. The guys on yellowbullet are saying there isn't much rhyme or reason to which ones do it. I think I've experienced it, but never investigated further than to swap the coils out for IGN-1As and having no more issues with no other changes. I've also run several engines, piston and rotary, with the D585s cranked up to 6.0ms and had no issues. I'll just never take the chance again with them.

- Subjective, my SOP, feeling is that the IGN-1A works better with stupid rich mixtures than any of the GM coils. Perhaps the spark duration is the reason? In rotary applications, my experience has been, that the D585s misfire at anything fatter than 11:1 AFR. I don't typically tune most applications to the fat side of 11:1, but when trimming in a scratch tune it happens. I've run the IGN-1As through similar processes without much issue of misfire. The LS1s? Don't even bother!

- Would be interested to see the results of the CDI output with a CDI specific coil. The high internal resistance of the FD coil is certainly limiting output. I'm still of the mind that there is no benefit to CDI for most applications compared to modern inductive coils. But a full blown, proper test would be interesting.
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Old 05-30-13, 04:29 PM
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I'm also curious about your test rig. What are you using to supply power to the coils?
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Old 05-30-13, 04:45 PM
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Originally Posted by 23Racer View Post
So what I am trying to understand is that with my relatively high revving 13B 1/2 bridge (8500-9000) are the stock FC coils inhibiting my higher rpm range? I always felt that the MSD wasn't a help, but should I convert to RX8 coils as they are designed for the rpm ranges I am in? I know these are simplistic questions, but I am looking for a broad brush type of answer.

Eric
possibly. we know the FC coil takes about 1ms to discharge, and we want dwell around 3.5ms, that's 4.5ms to complete a firing.

@9000rpm there is 6.6ms to complete each cycle, but with wastespark you need to fire twice, 3.3ms.

the discharge time drops with dwell, lets say .8ms = 1.6ms to fire twice, this only leaves 1.7ms to charge the coil TWICE.

by contrast the Rx8 coil @4ms dwell only takes .5ms to discharge, so @9000rpm its still has 2ms to do its taxes, or clean the fridge or something

feel free to check my maths, i played a pilot, not an engineer
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Old 05-30-13, 06:12 PM
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Originally Posted by t-von View Post
Wholy sh*t I totally understood that. Thx! I have a set of Fc coils for my 20b that I tried out at one point and noticed a small drop in power over the Ls1's. Now I wonder how well fc coils would perform in this test with an amp? Could they maintain the same duration with a hotter spark? I'm getting ready to eliminate my power steering and can build a nice bracket to hold those larger coils in the old power steering pump location.
that is what i want to try next, more voltage to the coil. were you boosted or n/a, and were you using the same charge times? Teh LS1's do look bigger than the LS2 truck coil, so maybe they have better duration

Originally Posted by 23Racer View Post
So what I am trying to understand is that with my relatively high revving 13B 1/2 bridge (8500-9000) are the stock FC coils inhibiting my higher rpm range? I always felt that the MSD wasn't a help, but should I convert to RX8 coils as they are designed for the rpm ranges I am in? I know these are simplistic questions, but I am looking for a broad brush type of answer.

Eric
that is a tough call, i think the only way to know for sure is try them out. i suspect they will help above 8000 rpm, but cold starts and low rpm will suffer a bit. When i swapped from IGN-1A's back to FC's i noticed cold starts and idle was smoother. before i had to give it throttle after starting for a couple seconds to prevent it from stalling, now it starts up and runs smooth on its own


Originally Posted by C. Ludwig View Post
I'm also curious about your test rig. What are you using to supply power to the coils?
i am using an R/C 11.1V, 45C Li-on battery.. fully charged it puts out a little over 12V. I was using a power supply, but it was hitting the current limiter and affecting the results, so i switched to the battery
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Old 05-31-13, 12:04 AM
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Originally Posted by gxl90rx7 View Post
that is what i want to try next, more voltage to the coil. were you boosted or n/a, and were you using the same charge times? Teh LS1's do look bigger than the LS2 truck coil, so maybe they have better duration

I'm NA. The truck coils I have are a used full set I got locally.

Originally Posted by gxl90rx7 View Post
that is a tough call, i think the only way to know for sure is try them out. i suspect they will help above 8000 rpm, but cold starts and low rpm will suffer a bit. When i swapped from IGN-1A's back to FC's i noticed cold starts and idle was smoother. before i had to give it throttle after starting for a couple seconds to prevent it from stalling, now it starts up and runs smooth on its own

I had the same easier starting with the fc coils when compared to the Ls coils. Now I did hear that the LS coils need more min battery voltage to turn on. Something like 10-11volts compared to the 9volts the fc coils needed to start working. So voltage drop during start-up made a huge difference with the Ls coils. My little Miata battery didn't help voltage drop either.
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Old 05-31-13, 10:19 AM
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Originally Posted by j9fd3s View Post
possibly. we know the FC coil takes about 1ms to discharge, and we want dwell around 3.5ms, that's 4.5ms to complete a firing.

@9000rpm there is 6.6ms to complete each cycle, but with wastespark you need to fire twice, 3.3ms.

the discharge time drops with dwell, lets say .8ms = 1.6ms to fire twice, this only leaves 1.7ms to charge the coil TWICE.

by contrast the Rx8 coil @4ms dwell only takes .5ms to discharge, so @9000rpm its still has 2ms to do its taxes, or clean the fridge or something

feel free to check my maths, i played a pilot, not an engineer
Really interesting. I have noticed that with my present setup of FC coils, every power run I make on the dyno goes all shaky above 8,000 rpm. Its like the car has tremors or something. When I changed the plugs to race plugs the point that the tremors started was a bit higher, like 8200 rpm, but the tremors were still there. I have a set of 3 Gen II LT motor coils from my other car that are spares at this time. It may be interesting to run them and see what difference they make. They were good on the Cougar to 9,000 rpm.

Can you increase the base voltage to an FC coil (like 16 volts) and produce a hotter spark? I know that this is done with the Standard GM and Ford roundy round guys as a cheap way to get more stable higher rpm power.

Eric
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Old 05-31-13, 12:02 PM
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yes, on any engine combustion pressure peaks at the torque peak and then falls off. so the ignition power you need goes down (or flat lines). this works ok on a stock 160hp engine that peaks @4500, but if you're making real power up top, things are different.

the race plugs should help as they take less voltage to fire, i'll post up the graph from the SAE paper.

increasing the voltage does help, more voltage in more voltage out? (i played a pilot, remember)

i was thinking ohms law applied, although it doesn't have the time constraint we want.
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Old 05-31-13, 01:42 PM
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hmm i tried increasing coil voltage up to 30V, but the output stayed the same. not sure why
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Old 05-31-13, 04:22 PM
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Originally Posted by gxl90rx7 View Post
hmm i tried increasing coil voltage up to 30V, but the output stayed the same. not sure why

On which coils?
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Old 05-31-13, 05:44 PM
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i figured it out. the ignitor i was using was hitting its current limiter a lot sooner with the higher voltage, so the output was not changing. But the coil was charged a lot quicker. So running 30V to the coil results in full output with only 1ms charge time vs 4ms at 12V

here is helpful reading on how coils work..
http://www.gofastforless.com/ignition/howig.htm

i did not realize the combustion chamber environment determines how much voltage the coil outputs. basically when the ignitor fires the coil, the coil voltage starts ramping up to whatever the threshold voltage is that will jump the plug gap.. as soon as the spark is started, whatever energy is left in the coil determines spark duration
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Old 06-01-13, 02:52 AM
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This has made for very interesting reading. I run an FC leading coil only (no trailing) on my 13b bridgeport and I have noticed that it seems to get lethargic at high rpm. Now I'm beginning to think that it is a pitfall of the wasted spark configuration of this coil.
Is it possibly the case that this coil doesn't have enough recovery/charge time at high rpm's to be causing a performance deficit? Hmm.. I might have to look at changing to COP with some IGN-1A's, or is there something better suited? What about FC trailing coils used as COP for leading?

Additional info; I'm using a max dwell setting of 3.0ms on my megasquirt2 v3 using the stock fc ignitor.
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Old 06-01-13, 03:44 PM
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lots of good (and surprisingly comprehensible) information here. I've always been intimidated and just downright dumb when it came to how coils actually work. I now have many pieces of the puzzle now.

much thanks to j9fd3s and gxl90rx7.
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Old 06-01-13, 04:12 PM
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Originally Posted by diabolical1 View Post
lots of good (and surprisingly comprehensible) information here. I've always been intimidated and just downright dumb when it came to how coils actually work. I now have many pieces of the puzzle now.

much thanks to j9fd3s and gxl90rx7.
gxl90rx7 did all the testing, so he should get the credit for this, all i did was ask a couple of questions
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Old 06-01-13, 07:36 PM
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Originally Posted by .::evil inside::. View Post
This has made for very interesting reading. I run an FC leading coil only (no trailing) on my 13b bridgeport and I have noticed that it seems to get lethargic at high rpm. Now I'm beginning to think that it is a pitfall of the wasted spark configuration of this coil.
Is it possibly the case that this coil doesn't have enough recovery/charge time at high rpm's to be causing a performance deficit? Hmm.. I might have to look at changing to COP with some IGN-1A's, or is there something better suited? What about FC trailing coils used as COP for leading?

Additional info; I'm using a max dwell setting of 3.0ms on my megasquirt2 v3 using the stock fc ignitor.
Currently using four leading ignitor and four trailing coils, COP, direct fire. Works great! 3.5 ms charge time. No issues at 10,000rpms
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Old 06-01-13, 07:40 PM
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Originally Posted by 23Racer View Post
Really interesting. I have noticed that with my present setup of FC coils, every power run I make on the dyno goes all shaky above 8,000 rpm. Its like the car has tremors or something. When I changed the plugs to race plugs the point that the tremors started was a bit higher, like 8200 rpm, but the tremors were still there. I have a set of 3 Gen II LT motor coils from my other car that are spares at this time. It may be interesting to run them and see what difference they make. They were good on the Cougar to 9,000 rpm.

Can you increase the base voltage to an FC coil (like 16 volts) and produce a hotter spark? I know that this is done with the Standard GM and Ford roundy round guys as a cheap way to get more stable higher rpm power.

Eric
Remember piston motor with COP fires the plug 4500 times at 9000rpms
Rotary motor with direct fire fires the plug 9000 times at 9000rpms
Rotary motor with waste spark fires the plug 18,000 times at 9000rpms.
Think that's correct.
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