Coil Dwell Time: ACDelco D576 and D555

[85_Olds_Ciera]

Maybe an old question, but at 14 Volts, anyone know what GM uses for maximum dwell time for each one? ACDelco D576 and D555

Any spec-sheet or table-listings?

thx

[robertisaar]

with the waste-spark DIS coils, dwell time is entirely(or almost entirely) controlled by the ICM. it monitors for coil saturation and adjusts the next dwell period to correct for overshoot/undershoot(likely with some intentional overshoot for stability purposes).

if the ECM were to suddenly change the desired advance and the EST line drops a lot sooner(more advanced spark), then there may be a weak spark event or even a misfire, but that is about the extent of direct control the ECM has on them.

[85_Olds_Ciera]

with the waste-spark DIS coils, dwell time is entirely(or almost entirely) controlled by the ICM...

I looking for specific data, as in using it via MegaSquirt. I would assume there is a Voltage vs Coil Dwell table, like this one for LS1 and 2004 Silverado 5.3 dwell table:

I don't like what I see in this discussion.

I like data, like in this information sheet; For coil charge time, the LS2 takes 4ms at 14 volts, and the LS9 takes 2.6 ms at 14 volts.

thanks for tidbits

[robertisaar]

if you're still using the ICM unmodified, then as long as you feed the ICM a reasonable dwell signal on the EST circuit, then it takes care of it.

if you gut the ICM and directly controls the coils, then you're kind of on your own with proper dwell times. GM released acceptable primary resistance specs, but not inductance, so determining saturation time is either going to be via sillyscope or trial/error. otherwise, you MIGHT find a couple of aftermarket manufacturers that have a listed inductance for their versions. I seem to remember someone with a Goldwing testing a coil or two for use on their bike and posting decent info.

[85_Olds_Ciera]

...on your own with proper dwell times....

Tidbit - EST - The ECM calculates ignition timing corrections and sends that information back to the module on the EST line (white wire). This information is used by the ICM to fire the secondary at the correct time.

Yes, just wanting to use coils only....maximum dwell for D555 may be 4 ms, which is found in lower RPMs. Exceeding 4 ms may heat the coil.

D576 is suppose to deliver about 5,000 volts more, but its safe dwell time is lower...one forum post suggested 2.5 ms, but I think that's a pinch on fast side.

thx again...

[robertisaar]

http://home.comcast.net/~loudgpz/GPZweb/Ignition/CBheiModCavCoil.html

http://home.comcast.net/~loudgpz/GPZweb/Ignition/IgnitionCoils/IgnitionCoils.html

you may find some useful info in those. his measured dwell times are considerably shorter than what I remember.

[85_Olds_Ciera]

his measured dwell times are considerably shorter than what I remember.

If all coils are examined, coil charge time will vary from 2 ms to 6 ms. On these EFI engines, its best to get an OEM or its equivalent.

As noted when using a "Mapped dwell (ECU has actual control of the dwell)" setup:

NEVER substitute the coil for another type on a mapped system. The ECU will not know you have done this and will still turn the coil on for a certain time, if your new coil charges quicker (lower inductance) then the coil or ECU will be damaged. If a slower charging coil is fitted (higher inductance) you will get a poor spark."

GM's HEI 'in-cap' coil,and GM's 7-pin module both have 3.5 milliseconds dwell; on the 4-pin module, it will vary the dwell time. Bosch had an aftermarket ignition module which did the same thing...higher dwell at idle, and lower at higher RPMs.

On a 4 cylinder Volvo-240 engine with Bosch LH 2.4 (fuel) & EZ116K (ignition), from idle to high RPM....I measured with MAC Tool Automotive Multimeter, just less than 6 ms at idle to 3.5 ms at 6,000 RPM or so.

Trivial Tidbits

- ROLLOFF - No matter whether you have a points ignition or an electronic ignition, both are inductive, and all inductive ignition systems are sensitive to what is called roll off. Somewhere between 3000 and 3500 RPM, the input current to the primary begins to drop off because the recharge time is insufficient.

- 10. At 900 rpm it takes 4.629 milliseconds for the crank to travel the 25 degrees from 10 degrees before TDC to 15 degrees after TDC. At 6,000 rpm this movement takes just 0.694 milliseconds. Remembering that the flame front has a constant burn rate then to have the flame front and piston converge when the piston is just after TDC requires the combustion process to start earlier in the cycle at higher rpm. Otherwise the piston would be lower down in its location before the flame front reached it.

On that motorcycle setup, I would have to think about that setup; that HEI module is only reading 2 cylinders....this module "knows" the engine RPM, and will adjust coil dwell based upon RPM, but each HEI module is not seeing true RPM. If you look at his Results, and multiply them times two (At 1000 RPM, the dwell time will be about 1.8 msec....so 3.6 ms), it might make more sense. From what I've read about HEI's module, his information is not in-line. I've heard the 3.5ms dwell elsewhere. GM made HEI modules for 4/6/8 cylinders, but these were setup for pickup coil to get AC signal on 4/6/8 lobes setup, not two lobes on his bike.

[85_Olds_Ciera]

his measured dwell times are considerably shorter than what I remember.

In this PDF, are what today's state of the art coils can do.

See: Primary Charge Time (14 V) on top of page five; the values range from 2.0 ms to 3.4 ms

Hence, his findings/opinions are not grounded in reality....either bad test equipment, calculations, etc.

[robertisaar]

like I mentioned before, kind of on your own. using the info provided for the GM DIS coil, assuming 2.8mH and 14V applied with a 5.5amp current limit, I'm actually calculating 1.1mSec to reach the current limit, he states 1.2.

[85_Olds_Ciera]

...GM DIS coil, assuming 2.8mH and 14V applied with a 5.5amp current limit, I'm actually calculating 1.1mSec to reach the current limit, he states 1.2.

Like I said, "I would have to think about that setup." MS users decided 2.5 ms was a good dwell time to use. But, after scanning his notes, he is not using the bias voltage output at W, which he notes this normally would "extend the dwell angle at higher RPMs to provide adequate dwell time for multi-cylinder engines." This statement is untrue, dwell time is shorten with RPM.

So, under this hacked module, the normal timing parameters are altered.

thx again

[85_Olds_Ciera]

lGM DIS coil, assuming 2.8mH...

Btw, Determining Your Maximum Dwell Setting


I wish I had these details...

[85_Olds_Ciera]

his measured dwell times are considerably shorter than what I remember.

FWIW, two URLs on this topic:

1. GM HEI: Cheap and Extremely Effective Ignition Upgrade...Mar 15, 2011

2. GM HEI & Coil Information

First URL is a repeat of what you cited, but second URL has more details. In 2003, he suggested original 4-pin module had about 5 amps, but there are/were aftermarket modules with "saturation time of ~2.4ms (@ 7.5 amps - storing ~112 mJ)."

Thanks again, for the tidbits.

[robertisaar]

I actually searched for this exact information a couple of years ago and this was about as far as I got. there just isn't any factory documentation and not a whole lot of people with the desire to find out have the equipment necessary to get solid baseline data..... or they're just not posting it, hard to tell.

[85_Olds_Ciera]

...there just isn't any factory documentation and not a whole lot of people with the desire to find out....

I figured out what he is doing (not why it works), and in his setup he is getting full charge time to the coil, but slower coils could have been used. So, in essence, he is getting full spark energy thru RPM range.

In this document, they use Hz, and 333 Hz = 5000 RPM. So, to convert 5000 / 333 = 15.01501501501502, so do this calc, and store this result into your calculator's memory. Then multiply this number by Hz shown on spec sheet.

Examples, rounded off

33 Hz = 495 RPM
133 Hz = 2000 RPM

Each HEI module is only seeing two lobes per crank revolution, instead of 4/6/8 lobes generating an AC signal for each crank rotation. Hence, his setup is generating a much lower frequency at a given RPM.

On page two is a table, and examine the voltage table for "Ignition Coil Current Peak, Cranking RPM 2.0 Hz to 27 Hz." At 10 volts, a full 5.5 amps can be stored when running 30 RPM to 405 RPM, but these modules are seeing a lower RPM in his setup. So, these coils are fully charged.

See table for "Ignition Coil Current Peak, Normal RPM." At about 200 Hz (3003 RPM), an automobile's single coil could still be upto full charge.

If I've done my math right (divide RPM by 4 ), the motorcycle's actual RPM has this relationship with what the module sees:

3,000 RPM = 750 RPM (module)
6,000 RPM = 1500 RPM (module)
9,999 RPM = 2500 RPM (module)

So, full current to coil.

When he says "..provide the coil with about 1.4 msec of dwell for every spark," the table for "Ignition Coil Current Peak, Normal RPM" indicates that the coil's charge time (dwell in ms) is based upon frequency, what the relutor produces. You can not measure dwell on HEI module, but it can be measured via coil's dwell time. You have to have that frequency to drive that circuit.