Anyone played with Spark dwell times?

[Tordne]

I've been reading a few interesting things about the Spark Dwell tables and people increasing the values to produce a more powerful spark.

It is probably common for us to change the plug wires to after market kits. I personally have Taylor ThunderVolt 10.4mm wires.

From talking to Jesse (Wait4Me Performance) while he was in NZ a while ago he mentioned that this is not necessarily a good thing to do as the stock wires are about the best you can get, and obviously tuned for the stock dwell.

I guess my interest is has anyone increased the Spark Dwell table, by how much and did the coils take it/last?

[wait4me]

:) The coil starves for charge at higher rpms with aftermarket less resistance wires, but has a stronger charge at lower rpms.

With stock wires and the stock coil dwell settings the spark energy is the same from low rpms to high. Due to the amount of energy still in reserve for the next event.

Same example goes for the 98-00 vortec computers. The limiter is actually caused from invalid spark dwell. Not an actual speed limiter in the pcm.

If you can measure charge voltages and spark intesity across the gap on a spark plug with after market and stock wires, you will see what the need is to be modifiying the dwell.

[wait4me]

On another note though, if you are stock, you wont see a power gain, it just allows you to run a Larger spark Electrode gap. Then you would see the gain.

[SSpdDmon]

So Jesse, I'm running TR55's @ the factory .055 gap and stock wires. Should I just leave well enough alone?

[Tordne]

I have TR6 plugs. So are you saying the increasing the gap you'd see a gain even if stock?

I recall you mentioning something about me running the 10.4 mm wires and that changing the effect of the dwell times etc :)

[joecar]

When you increase spark gap, it takes more voltage to jump thw wider gap...

so the spark voltage will be a little higher.

[joecar]

What the spiral wound wires do is contain all the EM energy within the spiral core, so no energy is lost as EMI, so all the energy is available for pushing spark (rather than also inducing currents in surrounding metallic objects).

[wait4me]

What the spiral wound wires do is contain all the EM energy within the spiral core, so no energy is lost as EMI, so all the energy is available for pushing spark (rather than also inducing currents in surrounding metallic objects).



My point is though, that with the stock dwell settings, they are set up expecting a 700ish ohm resistance, so they dont dump the reserve voltage as fast. With a wire that has 125 ohms, the voltage gets cleared out faster from the coil so it has to take longer to fill that lost voltage back in. Hence why it starves on the top end of the rpms and has stronger on the low rpms range.

[Redline Motorsports]

I guess the moral of the story is keep the stock wires on as they get the job done pretty good!

Howard

[wait4me]

I guess the moral of the story is keep the stock wires on as they get the job done pretty good!

Howard


:) I have yet to see proof of bigger wires making more power at WOT

[jfpilla]

Jesse,
While on the subject of spark dwell.
Have you compared the LS7 vs LS1 'spark dwell time" tables? The LS7 values are lower and so far no one knows why. I have an LS7 crate in my 2003 C5 and am using the LS7 tables. Do you know if that's the right thing to do? It runs fine. No apparent negative results, so far.
Joe

[SSpdDmon]

Jesse,
While on the subject of spark dwell.
Have you compared the LS7 vs LS1 'spark dwell time" tables? The LS7 values are lower and so far no one knows why. I have an LS7 crate in my 2003 C5 and am using the LS7 tables. Do you know if that's the right thing to do? It runs fine. No apparent negative results, so far.
Joe
Are the coil packs different (LS1 vs. LS7)??

[wait4me]

Every coil is just like a fuel injector, they all need different things to make them right just like an injector.

[jfpilla]

Every coil is just like a fuel injector, they all need different things to make them right just like an injector.

We are all guessing that's the case and hopefully is the reason. What would you look for regarding results. Plug color, backfires, missing at WOT, etc? Or, is there a known voltage to measure?
Joe

[jfpilla]

Are the coil packs different (LS1 vs. LS7)??

Yes, but how they differ is a question.

[joecar]

My point is though, that with the stock dwell settings, they are set up expecting a 700ish ohm resistance, so they dont dump the reserve voltage as fast. With a wire that has 125 ohms, the voltage gets cleared out faster from the coil so it has to take longer to fill that lost voltage back in. Hence why it starves on the top end of the rpms and has stronger on the low rpms range.Ah, I get it. :lightbulb:

[wait4me]

Increasing the power output of the coil just allows you to open the gap more on the plug. Same kind of example when you go with an aftermarket msd ignition on the older gm stuff. It wont show a difference unless you raise the plug gap. The larger the spark the more the power due to better fuel ignition.

[oztracktuning]

My engine is experiencing spark blow out at higher boost levels. The solution thats common is to decrease the gaps. can i increase the dwell values at high rpm and solve the problem an alternative way?? Its an E38 ,using TR6 gapped near 0.9mm (0.035")

[neil]

Hi Steve,
I don't know whether increasing the dwell would help your problem.
I would have thought that you would need to increase the current and if required the dwell rather that increase just the dwell. If the spark is blown out I think you would need to increase the strength of the spark (ie. current) to overcome the problem. To me decreasing the gap would cause other problems.
Just my 2 cents.

Neil.

[oztracktuning]

Thanks Neil for the input. Gapping the plugs smaller is the common thing that people need to do when increasing boost. Mine are gapped at 0.8mm now but its common for them to be 0.65mm, this is with GenIII/IV and also lots of Turbo imports. The question is if the dwell is near the lower limits of coil function which i am told it is. If so more dwell is supposed to be able to help, its already optimal as you have said it wont.

[The Alchemist]

just use an amps clamp on the 12v in and measure charge time to were it current limits > easy < charging past this point ie more dwell just overheats the coil
just google coil & current probe for a detailed explanation.
We do it all the time to set dwell with aftermarket ECu's and different coil combo's.
Cheers,
Mike

[jfpilla]

http://www.megamanual.com/seq/coils.htm

Can someone look at this site and in particular scroll down and watch the video.(it's linked)
The tester says the max ms for LS2 coils is 5.0. That's 2x stock at high rpms. Hopefully explain, in laymans language, why he would come to that conclusion?
Is there anything to gain by increasing plug gap and dwell time for a stock LS7, givin what he concludes?

[swingtan]

Maybe a quick summary of the Kettering ignition system is needed, as well as some basic electrical theory....

What is the coil used for?


The coil in the ignition system is used to increase the voltage from the supplied 12v ( nominal ) to a voltage that will jump the air gap on the spark plug. The reason for needing the spark is that it creates an ionised "plasma" that is hot enough to ignite the air / fuel mixture in the cylinder.


How does it work?


The coil is just a transformer. It has a primary side and a secondary side, or a primary winding ( coil ) and a secondary winding ( coil ). The ratio between the primary and secondary determines how the transformer converts the voltage applied to the primary. More turns of wire in the primary than the secondary results in "less" voltage produced out of the secondary. More windings in the secondary than the primary results in "more" voltage being produced out of the secondary.

The ratio is between windings and voltage is directly proportional, 2 times more windings in the secondary means 2 times more voltage ( all other factors being equal ). So the "coils" used for the ignition system obviously have a large number of turns on the secondary compared to the primary.

Those that know a bit about transformers will also know that they only work when the voltage is changing. Apply a constant 12V to a car coil and you get nothing out of it. Disconnect the power and you get a nice spark at the time the power is removed. So remember that the spark occurs when the power to the primary is "cut", not when the power is applied.


So what is dwell?


Dwell is the term given to the time between when power is applied to the coil, and when the power is cut. So you need to work backward from the "spark event" to when the power was actually applied. Dwell can also be thought of as the "charge time" for the coil. Think of it like this...

When power is applied to the coil, the coil builds up a magnetic field around its self. If left long enough, the magnetic field will grow till a point is reached where the coil core is "saturated" and the field no longer grows. For a transformer, a saturated core is a bad thing. It reduces efficiency greatly and should be avoided at all costs. Saturating the core will eventually result in a dead coil.

When the power is removed, the magnetic field collapses rapidly. the collapse occurs much faster than the charge and as the field collapses, it generates a high voltage in the secondary. Voltage in a coil is directly proportional to...

The number of turns in the coil
The strength of the magnetic field
The speed at which the magnetic field changes

The last point explains why you don't get a spark when the power is applied, the creation of the magnetic field takes longer than the collapse.


Optimal dwell?


Optimal dwell is the point where the coil produces the maximum magnetic field without saturating the core. As already mentioned, there is some "residual charge" remaining after a spark event. Any power not expended as spark is reabsorbed back into the coil and can be used to start charging the coil again, but it can have other issues. Too much dwell time will result in a saturated core, resulting in an over heated coil and possibly a miss-timed spark. Too little dwell time will result in insufficient coil charging and a weak spark.


How do you tell the difference?
[indent]
The reason this thread exists..... I'm sure you could calculate the optimal dwell time given all the specs of the components involved.

The coil resistance, inductance and capacitance
wire resistance between the coil and the battery / PCM
resistance, capacitance of the PCM switching CCT
Ignition lead resistance
expected plug gap

I think it would be rather difficult though. If I was going to test dwell times, I'd hook up a portable Cathode Ray Oscilloscope ( CRO ) and measure the spark waveform at different engine speeds and loads. This would allow you to see what dwell times were producing the highest possible spark voltage. You could also use it to measure the primary coil voltage to get an indication of where the coil starts to saturate.

If you look at the stock timings, the dwell time is probably set the way it is to protect the coils from over heating more than provide the highest possible spark voltage. This is why the dwell time drops as the RPM's increase, more spark events mean more power is applied to the coils making them hotter. FWIW, at 7000RPM, the time between spark events for a single coil is about 17mS ( 7000 RPM in a 4 stroke motor is 3500 sparks per min. for any given cylinder. This is 58.3 sparks per second or one spark every 17mS ).

There is a lot more in this, this is just a quick overview......

Simon.

[jfpilla]

If you look at the stock timings, the dwell time is probably set the way it is to protect the coils from over heating more than provide the highest possible spark voltage.

Simon,
I understand, in a non technical way, what you descibe.
My questions are:
-In the video, the tester says 5.0 is optimum for ls2 coil packs. That's
double stock settings for an LS7. Is that a type of increase that could
hurt the coil packs?
-I have no sense of what a % increase in dwell means. ie: Is 10% a lot or
not very Much?
-As you say about dwell probably set to protect, is there any value to
increasing dwell times and spark gap with a stock or will it not make
much, if any, difference?
Thanks for the response.
Joe

[swingtan]

-In the video, the tester says 5.0 is optimum for ls2 coil packs. That's
double stock settings for an LS7. Is that a type of increase that could
hurt the coil packs?
-I have no sense of what a % increase in dwell means. ie: Is 10% a lot or
not very Much?
-As you say about dwell probably set to protect, is there any value to
increasing dwell times and spark gap with a stock or will it not make
much, if any, difference?
Thanks for the response.
Joe

First point, he's talking LS2 "TRUCK" coils. While I haven't seen the stock LS7 coil packs, I'm assuming that they are not LS2 "truck" coil packs though. The testing in the video shows how the different coils behave when tested on the bench. This may not translate well to being in a hot engine bay, when you are stuck in traffic with the air con running. The video clearly shows that excessive dwell gives no benefit in produced spark though, it would have been good to get some coil temp readings for prolonged running at a given dwell.

Could it hurt the coil packs? Well, I'm guessing that it could hurt the LS1 style coil pack as that may have been why it died. The LS2 type may be OK and the "truck" coil has a nice heat sink that would help cool it.

I can't say if 10% is a lot or not as it really depends on the driving you are doing. It may be an idea to increase the dwell a bit for a trip to the drags and then drop it back again for normal daily driving. Or maybe increase the dwell in the higher RPM's to bet the benefit there, and then allow the coils to cool a bit when driving at lower speeds. There are lots of ways you could attack this.

I'd say that if you are not having fuel ignition problems, then there is not a huge reason to play with the settings. Maybe if you use after market leads, you may need to adjust. Changing the plug gaps also "may" require a touch up on the dwell, but my primary rule would be "if it's working, don't touch it". Sure you may get a marginal increase in power through better ignition, but you would possibly get more power by indexing the plugs.

Looking at some E38 tunes shows that dwell time is normally reduced as RPM increases. Again I think this has more to do with keeping the coil pack cool than anything else. If you could keep the coils cool by other means, ( removed engine covers, relocating, heat-sinks etc ), then a slight increase in dwell time could be of some advantage.

Simon.

Another point, you need to reference the dwell time to the voltage applied to the coil as well. In your car, the voltage will change a bit depending on what is happening ( engine speed, battery charging, electrical load etc ). It's probably a good idea to log battery voltage to see what the typical supplied voltage is to the coils under different conditions. More battery voltage will result in more power being supplied to the coil, so a longer dwell time may saturate the coil under some conditions, but not all.

[macca_779]

I upped the dwell across the board on my LS1 5% and run a 1.6mm gap. No noticeable increase in power but certainly not a reduction either. I've run them like this for over 2 years now and haven't had a coil pack fail yet. I've got no technical info as to why I choose 5%.. It just seemed like a small enough percentage at the time.

[jfpilla]

Thanks for the input.The car runs great with no misses. There doesn't seem to be much to gain, if any. I would say leave well enough alone.

[joecar]

This is one of the areas where GM engineers have invested man-decades (or man-centuries) of work.

[Chuck CoW]

:) I have yet to see proof of bigger wires making more power at WOT

Yup...Same here. I always use stock wires and even plugs for NA vehicles with no problems.

Chuck CoW

[GAMEOVER]

Yup...Same here. I always use stock wires and even plugs for NA vehicles with no problems.

Chuck CoW

Me too. I always use stock wires and plugs too...:)