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Coil Packs and Dwell Time

belize1334

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I've been reading threads about dwell time ever since I put in my COP setup. It runs quite well actually but I wanted to be sure that I'm not giving up performance in ways that I don't notice.

The primary argument against COP seems to be that, when wired in series, the Intrepid/300m coils don't have the same dwell time as OEM coils and so they don't fully charge in time for the ignition event. In parallel their dwell times are lower than the OEM coil-pack (or so I heard) and are thus able to full charge... but the igniter can't handle the current draw from a 0.5 Ohm impedance load.

So here's my thought. Clearly the intrepid/300m coils were meant to be charge at 12v since they're not actually intended for wasted spark. So, drop the "wiring in series in order to protect the ingiter" philosophy and address the problem of the igniter not being stout enough to handle the load from two coils. How about running two OEM igniters in parallel, each driving a different "bank" of coils. That is, two igniters being driven by the same ECU signal, but with outputs for 1-3 and 2-4 respectively. Or, alternatively, run the two igniters in TRUE parallel with input and outputs fully shared so that they behave as one and then run the coils in parallel as well.

Would two igniters play nice if they were driven off of the same ECU output? Since they're transistors I don't imagine they would draw too much current from the ECU... but would they interfere with each other? /ubbthreads/images/graemlins/dunno.gif
 
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prove_it

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I have wondered about running the same set-up with my COP two.
I hope this thread continues and gets deep and full of knowledge.
 

belize1334

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I've got an extra 1G coil that I'll take down to the EE lab and test the inductance of the primary coil. Then I'll pull my COP and do the same. This should settle, for once and for all, how the charge time requirements of the chrysler coils compare to OEM coils and whether the stock dwell times should be altered when running COP.

As for the voltage issue, I don't see how the chrysler coils could possible store as much energy as OEM when configured in series as mine are. I'll be able to make a more exact statement to this effect once I've measure the inductance but my instinct tells me that if you want good spark then they should each see the full 12v. To that end I'm going to keep this dual-igniter in mind and see if I can get it set up and running.
 

prove_it

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Keep me posted, I am very interested in this and will be following you in this adventure. In the last few months it seems that everyone who was running COP set-ups have switched back, blaming the coils for weak spark issues. I know our factory transistor can't handle much without getting overloaded. I am using mine in series like everyone else. I love my COP due to the smoother idle.

Good work and thanks for getting into it and getting it all tested, I look forward to the results.
 

TurboTrader

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Pemberton, NJ
I have an automotive genius friend attempting the same thing with the two ignitors for his COP setup, 300m coils as well, IIRC. Will definitely update here if I hear any specific results from him. He is also planning some type of heatsink to keep them cool from what I understand.

I'm interested to see the results.

However, I still don't understand, even running two ingnitors, how it would be better than running a DIS-2, for example, with the COP setup, as it has not only been covered more, but many have yielded excellent results for those that do need the extra spark, despite our stock ignition setups being pretty good up to 500HP from what I understand. If it's not broke, why fix it?
 

broxma

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Oh ye of little faith.

click

Same post but actually got it working properly. System is still on my Evo and running like a champ. If you continue read from that point you see I made that system work very well. Post 90 in the same thread has all the part numbers from your local store.

I have a COP system right now but I am probably switching over to this system in the next few days.

Tell your friend with the heatsink idea that Ford coils off the new trucks already have a integrated heatsink. Also, we tried the dual ignitor system on a few cars and could never get it working proper. It became an issue with timing. Not engine timing, but timing between the coils. When you are talking periods in the range of 50ms, having two ignitor only a few ms out of sync screwed it up. He may have better luck however. I actually make mention of a dual ignitor idea in the EvoM post a bit into it.


/brox
 
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belize1334

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I do really like that setup and the fact that you've got it working with a DSM igniter makes it even more attractive. The reason that I'm continuing to try to get more out of my intrepid coils is that I like the clean install with no cables and I've already got the setup built.

As for the DIS-2, I don't think that there IS an advantage to dual igniters over something like that other than the fact that I can probably get on at the junk yard and have it all running for the cost of my soldering time. This is an adventure in cheap, DIY solutions to known issues.
 

broxma

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The Intrepid COP I built has worked decent thus far but I am now at a point where I am concerned about its ability to maintain spark. I am looking at two options.

First, buying brand new Intrepid coils. The ones I get are junkyard captures and while I have 50 of them, I know of no test procedure to differentiate between good and really good ones.

Second, just move over to the GM/Aurora coil setup using MSD coils. I have a set of VatoZone GM OEM replacement coils which would probably be fine but I think I am going to spend a little more on it this time since I am expecting more from the Galant than I did from the Evo.

If I could verify a coil with a higher natural voltage and better dwell time I would make a plate for them to test them out but information on such things is often not available. I do have some Toyota coils from a V6 Camry or something that appear beefy but who knows how they perform in reality.

/brox
 

belize1334

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More on this...

My current plan is to attempt to run a '90 Power TR (J122) in parallel with the '91+ Power TR (J722T) that I already have. My reasoning for this is that both units should satisfy the same energy demands but the '90 unit doesn't have the integrated tacho module which will (hopefully) avoid some confusion in terms of which unit is talking back to the ECU. Also, I have an extra '90 in my hand from the Talon that I parted and I figure the harness for it should be easier to find since people cut them out when switching to '91+ ignition setups. My only concern is getting the wiring to work out so I'm on to trying to understand the circuit diagrams...

According to the '90 FSM, the 5-pin power transistor operates as a variable ground for the primary coils which are always powered. The ecu sends a signal to pins 2 and 5 which close the pathways from pins 1 and 6 (respectively) to pin 3 which is a common ground.

By contrast, the '91+ power transistor appears to have two more pins which work in conjunction as the tacho module...



It looks like 7 and 2 open pathways from 8 and 1 (respectively) to 3 which is common ground. Then, there seams to be an on-board IC which buffers the signals from 8 and 1 to create an output signal. 6 would seem to be the VCC for this IC.

So, as far as I can tell wiring the '90 in parallel with the '91+ is as simple pin-mapping (2,5,1,6,3) from the '90 onto (7,2,8,1,3) on the '91+. This should essentially double the current rating of the "effective" system while leaving it's down-stream functionality untouched.

Anybody have a '90 plug/harness that they want to donate to this project?
 

toybreaker

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Apr 30, 2006
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Interesting project you guys are working on. /ubbthreads/images/graemlins/applause.gif

Quote:
Anybody have a '90 plug/harness that they want to donate to this project?



Pm me your shipping address, (and if you can wait untill monday,) I'll get one in the mail.
 

belize1334

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Nov 18, 2003
Messages
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Location
Bozeman, MT
More on this...

I just got back from the lab where I bench tested my current COP setup (intrepid coils wired in series) as well as my spare OEM coil-pack.

Intrepid coils in series:
Primary Resistance: 0.8 Ohm
Primary Inductance: 2.9 mH

OEM coils:
Primary Resistance: 0.8 Ohm
Primary Inductance: 3.9 mH

As you can see, the intrepid coils actually match the intended resistance of the OEM coils when wired in series. That means that, given sufficient charge time, both configurations would come to the same final current value of 15 Amps (I = V/R = 12v/0.8Ohm). Now, somebody quoted that the spec'd current is only 6 amps. This corresponds to a charge time of roughly (1/2) the characteristic time. So, if 6 Amps is in fact the typical current then the dwell time of the ECU is t=(1/2)L/R or ~1.75ms.

Now for the interesting bit...

I plotted the current as a function of time for both configurations (found by I=Io * (1-e^(t/tao))) and then plotted the stored energy for this current for each configuration (found by E = (1/2) L I^2). The results clearly show that for charge times shorter than the characteristic time of the OEM coils (just under 4 ms), the intrepid coils (with lower inductance) actual have a HIGHER stored energy... as the charge time decreases the effect is increased... as the charge time increases both currents move toward their asymptote of 15A and the OEM coils ultimately store ~33% more energy... but it takes a while. So, what this really tells us is that we need to know the ACTUAL dwell time that the ECU uses in order to state definitively whether the intrepid coils have a weaker spark when wired in series. But, for anything shorter than about 6 ms it's at least a wash and at best the intrepid coils have more energy than the OEM coil pack. One thing is for CERTAIN though! Wired in parallel, the intrepid coils would KILL the OEM coils in stored energy.

But, of course, there's more to the story. I wasn't able to measure the secondary inductance so I don't know the winding ratio. That means that we can't say for sure at this point how the energy is delivered. It may be that the intrepid coils have a longer duration spark that's not as hot...




EDIT: According to stealth316 the charge time of 3si motors is about 4ms and the current is regulated to cap at 6 amps. If that's true for our system as well then the intrepid coils would reach 6 amps faster but would be capped there just the same as the OEM coils. At that point, the stored energy of the intrepid coils would be roughly 75% of what's in the OEM coils. So, just plugging in a COP setup with coils in series and no other modifications you can expect to get about 75% of the stored energy as you do in an OEM setup. Running two igniters in parallel would raise the cap to 12 amps. Over 4ms the current through the intrepid coils would reach almost that value (11 amps). That means that the Intrepid coils would win again (even in series) for times less than 6 ms and would be a significant improvement over the OEM configuration (with a single igniter). Running the coils in parallel has no significant advantage at this point ( so long as the charge time never goes below 4ms) since the charge time is already enough to reach the capped current when run in series. If the dwell time allotted were to drop to below 4ms then the coils would no longer be reaching their capped current value and you'd start to lose energy. Run in parallel they reach the capped current in 1/4 the time so the dwell time becomes MORE than enough. This could itself be an issue as excessive dwell times create more heat in the coils and may lead to failure. One very useful thing to know at this point would be the rated current through the Intrepid ignition system. It may be that 11 amps is just way too much for these coils...
 
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broxma

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San Antonio Tx
The 91+ ignitor actually only has 7 wires if I recall. One is absent so the only extra wire would be the white tach wire.

My concern is wiring the ignitors in parallel is going to put a strain on whatever part of the ECU is powering it or will the extra power be isolated past the ignitor essentially using the ignitors as transformers of sort?

I am going to take my COP ignition off tonight and have a look see at how it is wired. I believe it is wired power to 1, out 1 to 4, and 4 to ground so a series configuration. 2 and 3 are set the same way. I have an extra ignitor in the garage and a harness for it. If you have a diagram wiring them in parallel I'll be happy to pull out the gun and solder it up to test it.

I am trying to visualize how to do that but I can't imagine it in my head. Are you taking output from one ignitor and feeding it to the input of the other?

What is the lim fac for wiring the coils in parallel? Possible overheat of the ignitor?

/brox
 
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belize1334

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For running the igniters in parallel I'm talking about take the ECU signal for 1/4 and 2/3 and splicing it to both igniters and then splicing the igniter outputs for those cylinders back together again. If you think of the igniters as relays, then I'm just talking about having both relays run off of the same signal and then having their outputs tied together to drive the same load. It is possible that two igniters could put extra load on the ECU but I highly doubt it. Normally a transistor switch draws effectively no current (on the order of micro-amps) so that shouldn't be an issue.
 

broxma

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Ok. I see what you are saying. Drop resistance of the ignitor with the parallel circuit, then the coils wired in series will see double power.

Well I can't do a scientific test of said system I can do a "does the car still break up" test tonight and report the findings. I'll even take video.

/brox
 

belize1334

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It's not so much dropping the resistance as it is sharing the duty. The coils will see the same voltage and provide the same resistance regardless of the igniter configuration. Having two igniters just means that each only has to supply half the current.

Now, the effects of that are a little unclear because I still can't find out for certain whether the igniters are current-regulated. As I mentioned, the stock coils reach 6 amps after only 2(ish) ms. If the dwell time is more like 4 or 5 ms (as suggested) then the current would rise to more like 15 amps. Now, if it's also true that the stock system is designed to have 6 amps through the coils... then the igniter itself must have some kind of internal regulation that keeps the current at or below 6 amps.

So, the result of running two igniters depends on whether they are individually current controlled. If the ARE, then doubling them up effectively doubles the max current that the coils are allowed to pull. This would raise the stored energy without having the run the coils in parallel. If the aren't, then the coils pull as much as they want already and doubling them up just lets us run the coils in a different configuration (to draw more power) without burning the igniters out (since they presumably have a max current rating).

But, as I showed above, if the igniters aren't current capped at 6 amps, then for charge times of less than 6 ms the intrepid coils already store more energy then OEM so there's no point in messing with anything... we're already winning. On the other hand, if the igniters ARE capped, then doubling them up raises the max current to 12 amps (which the intrepid coils will pull after 4 ms even without putting them in parallel) and triples the stored energy.

This leads me to conclude that there is no reason to rewire the coils themselves for parallel duty. The only improvement would instead come from doubling the igniters (in parallel) which will increase the energy of the spark by a factor of 3 if they're already current limited to 6 amps. If they're not, then it won't do anything.

Edit: I also finally found a thread which quotes dwell time for the stock ECU. Now, this is for a 2G mind you so I don't know if it's directly applicable. Can anybody comment on the difference between 1G and 2G ignition coils? dwell times
 
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broxma

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I suppose finding out if they are in fact current capped is going to be impossible to test for?

Since I have multiples of everything and enough parts to rebuild the ignition system 5 times over and a new ECU in case it blows, I will proceed with the install. Should only take me an hour or so. Steve and I just took the car out and it has a slight break up at high RPM which I am hoping will go away if the hypothesis is correct. If it does and we can repeat it a few times we can push this into theory land.

/brox
 

broxma

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I wired them up. The car defintely runs but I have a small exhaust leak at the turbo flange I need to tighten up before I head out. I'm going to leave the spark gap and boost where it is and see if I have any noticeable change.

/brox
 

prove_it

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Thats awesome, let us know asap>
 

broxma

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Alright let's lay out the conditions from earlier and compare.

About 3 hours ago - Temp about 92, Dry, 17 PSI, Single ignitor. Spark break up occurred at higher RPM above 6K till 9K randomly

Just now - Temp about 87, dry, 17 PSI, Dual ignitor. Full throttle pull in 3rd gear, no break up.

I cannot say for certain that it is the ignition because the variables have changed. I am going to crank up the boost to about 21 or so and see if I have break up. I had a noticeable increase in spark break up between 17 and 19 PSI today under similar environmental conditions. I would think this spark break up would be more pronounced given a further increase in boost. If someone disagrees with this let me know but sounds logical to me.

I will say this, the last run I just did on the highway here was in the identical locations I took Steve for a ride at earlier. This most recent run felt like a different car. It was smooth, and felt as strong as the car has ever felt. Chalking it up to the dual ignitor may be premature but it is certainly different in a positive way, very positive.

/brox
 
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