spark dwell...can somebody give heavy details

[stevebo17]

so when doing this you set the dwell time modifier vs map to 1? thats what mne is stock... Or did I misread?

[WS6FirebirdTA00]

you dont do anything, you leave it stock

[03Sierraslt]

So have any of you guys found out anything more on this? I just stumbled on this topic and have though of it before, but never changed my dwell. Being that I am running boost I am thinking that I might be able to gain something in the upper RPM by changing the dwell. Currently my spark dwell table is stock putting me in the 3.3 area from 16+ volts, from 10-16v I am 5.3 to 3.1 at 6000 RPM. I am trying to decide whether or not to up the dwell slightly.

[WS6FirebirdTA00]

You wont gain a thing, leave it alone

[Blades]

I'm going to bring this thread back up and ask if it would help cure a little misfire at idle.. I guess when I switch the factory wires out it'll be a useless tweak.

[WS6FirebirdTA00]

NO, just as my last post said, leave it alone.

[Blades]

Oh yeah? So a better spark wouldn't help misfire out? ok.

[WS6FirebirdTA00]

Oh yeah? So a better spark wouldn't help misfire out? ok.

Increasing dwell does not make it a better spark. If you over charge the coil you heat it more and it will hurt your spark. The coil charges enough as it is right now. If anything it would make a bigger difference, IMO, with more g/cyl. My tests showed zero gains or benefits.

[Blades]

Roger that. So whats the difference between increased dwell and new upgraded coil packs? Just how the spark fires?

[WS6FirebirdTA00]

Dwell is charge time if I remember correctly. If it is a coil designed to run like a stock one, then the dwell should not need to be changed.

[MNR-0]

I made up my own custom dwell map based off the known specs. of the coil. I researched the MSD Blaster Coils for the LS1, used these values to determine the charge time required at each voltage point.

COIL SPECIFICATIONS (MSD Blaster 2 SS)
TURNS RATIO: 52:1
PRIMARY RESISTANCE: .57 ohms
SECONDARY RESISTANCE: 3.1K ohms
INDUCTANCE: 5.8 mH
MAXIMUM VOLTAGE: 44,000 V
PEAK CURRENT: 150 mA
SPARK DURATION: 1200 uS

I used the Ignition Coil Circuit Simulation By Bowling & Grippo here ==> http://www.bgsoflex.com/igncoil.html to model my new dwell map.

I reverse interpolated the secondary coil capacitance from the voltage output of 44kV, worked out to be 155pF.

The inputs are beginning and ending RPM, RPM step, dwell angle in crankshaft degrees, resistance of primary ignition coil circuit in ohms, inductance of igntion coil primary in millihenries, battery voltage, and capacitance of ignition coil secondary in picofarads. This model assumes 100% energy transfer from primary circuit to secondary circuit, which will not be the case in the real world - expect 70-85%. To optimally charge these coils, I increased the ideal charge time by 1.176470588.

The stock tune leaves a little to be desired, but its not far off. With this map you zero out all the dwell modifiers.

I also believe there is no need to reduce dwell as RPMs rise. That's twisted. I reckon GM were trying to save on warranty returns here. A coil has a predetermined charge time - no matter what the RPM. The COP (Coil-on-plug) design means there is ample duration to charge at any RPM with these coils.

Comparing this to a stock tune, its easy to understand why some ppl. fry these coil packs, as the calibration requests too much dwell time at light throttle and retards it at the top end.

In mapping, I went for a flat amp. draw of about 7A per coil. Coupled with the injectors, thats 64A at idle. You need a decent battery and healthy alternator to use these babies.

MSD recommend running 2 heat range colder spark plugs, as theres a lot of energy being pumped in there.

Also note that MSD puts out 14kV more than stock coils. They do that by more windings. More windings means more charge time. If you go to the effort of rescaling your injector dead-time offsets for bigger injectors, why wouldn't you do the same for your coils?

[tjwong]

I made up my own custom dwell map based off the known specs. of the coil. I researched the MSD Blaster Coils for the LS1, used these values to determine the charge time required at each voltage point.

COIL SPECIFICATIONS (MSD Blaster 2 SS)
TURNS RATIO: 52:1
PRIMARY RESISTANCE: .57 ohms
SECONDARY RESISTANCE: 3.1K ohms
INDUCTANCE: 5.8 mH
MAXIMUM VOLTAGE: 44,000 V
PEAK CURRENT: 150 mA
SPARK DURATION: 1200 uS

I used the Ignition Coil Circuit Simulation By Bowling & Grippo here ==> http://www.bgsoflex.com/igncoil.html to model my new dwell map.

I reverse interpolated the secondary coil capacitance from the voltage output of 44kV, worked out to be 155pF.

The inputs are beginning and ending RPM, RPM step, dwell angle in crankshaft degrees, resistance of primary ignition coil circuit in ohms, inductance of igntion coil primary in millihenries, battery voltage, and capacitance of ignition coil secondary in picofarads. This model assumes 100% energy transfer from primary circuit to secondary circuit, which will not be the case in the real world - expect 70-85%. To optimally charge these coils, I increased the ideal charge time by 1.176470588.

The stock tune leaves a little to be desired, but its not far off. With this map you zero out all the dwell modifiers.

I also believe there is no need to reduce dwell as RPMs rise. That's twisted. I reckon GM were trying to save on warranty returns here. A coil has a predetermined charge time - no matter what the RPM. The COP (Coil-on-plug) design means there is ample duration to charge at any RPM with these coils.

Comparing this to a stock tune, its easy to understand why some ppl. fry these coil packs, as the calibration requests too much dwell time at light throttle and retards it at the top end.

In mapping, I went for a flat amp. draw of about 7A per coil. Coupled with the injectors, thats 64A at idle. You need a decent battery and healthy alternator to use these babies.

MSD recommend running 2 heat range colder spark plugs, as theres a lot of energy being pumped in there.

Also note that MSD puts out 14kV more than stock coils. They do that by more windings. More windings means more charge time. If you go to the effort of rescaling your injector dead-time offsets for bigger injectors, why wouldn't you do the same for your coils?

I was recently tuning a stand alone EFI system made by AEM. The application was on a Cobra replica car built by Superformance out of South Africa. The engine is a 427 Ford FE engine with TWM induction (weber style) EFI throttle bodies, and the ignition is set up using a cam and crank sync, with 8 MSD LSx coils. After tuning the car the owner experienced random misfires after extended drives, the condition was worse on hotter days. On the dyno the car rarely exhibited the problem as I could not continuously "drive" the car under load without it over heating.

After days and days of checking over everthing from finding intake manifold leaks, rebalancing the TB, sending the ECM back to AEM for them to check out. I finally called MSD to find out what their rated maximum dwell time is for their coils. After speaking to one of their developement engineers in El Paso, I was told that their coils were rated at 3.5ms maximum dwell time. In the AEM programming dwell was not clearly expressed, it was set up using two tables and one constant. So I had to call them again and tell them what I had found out about the MSD coils. After a lengthy discussion, they sent me new variables for the dwell setting. After loading the new variables the problem was solved and the customer was ecstatic.

Basically the coils were overheating and breaking down after extended drive times due to too much dwell. I have played with dwell settings in standard LSx based PCMs during dyno tuning sessions on my load bearing Mustang Chassis dyno. I have found no gains what so ever by increasing dwell. However if you reduce dwell you will start experiencing misfire conditions and extreme loss of power.

I do have GM Powertrain Engineering information on all their coils rat holed away somewhere. If anyone is interested I can find it. Don't ask how I got all this stuff, I just have it

[MNR-0]

I was recently tuning a stand alone EFI system made by AEM. The application was on a Cobra replica car built by Superformance out of South Africa. The engine is a 427 Ford FE engine with TWM induction (weber style) EFI throttle bodies, and the ignition is set up using a cam and crank sync, with 8 MSD LSx coils. After tuning the car the owner experienced random misfires after extended drives, the condition was worse on hotter days. On the dyno the car rarely exhibited the problem as I could not continuously "drive" the car under load without it over heating.

After days and days of checking over everthing from finding intake manifold leaks, rebalancing the TB, sending the ECM back to AEM for them to check out. I finally called MSD to find out what their rated maximum dwell time is for their coils. After speaking to one of their developement engineers in El Paso, I was told that their coils were rated at 3.5ms maximum dwell time. In the AEM programming dwell was not clearly expressed, it was set up using two tables and one constant. So I had to call them again and tell them what I had found out about the MSD coils. After a lengthy discussion, they sent me new variables for the dwell setting. After loading the new variables the problem was solved and the customer was ecstatic.

Basically the coils were overheating and breaking down after extended drive times due to too much dwell. I have played with dwell settings in standard LSx based PCMs during dyno tuning sessions on my load bearing Mustang Chassis dyno. I have found no gains what so ever by increasing dwell. However if you reduce dwell you will start experiencing misfire conditions and extreme loss of power.

I do have GM Powertrain Engineering information on all their coils rat holed away somewhere. If anyone is interested I can find it. Don't ask how I got all this stuff, I just have it

Sounds good. When you get a chance either pop me an email ([email protected]) or post them up.

Interesting about the 3ms dwell angle.

As far as I understand it, the goal is to fully charge the coil. Now on your feedback if you go less than 3ms then its being discharged before it has charged and that would understandably result in misfires. I would think a coil will overheat only if its holding the charge too long, that is, the dwell time is too long.

For comparison sake...

V_ stck custom
14 4.14 4.02ms
13 4.60 4.38ms
12 5.70 4.83ms
11 5.90 5.90ms

Ignition voltages will vary throughout normal daily driving activities, anywhere from 13.5-12.5V normally. Interestingly enough, this indicates to me the stock map has to much dwell! Perhaps why no gains going higher?

The retard at high RPM still gets me though...

[INTHERED]

What about an FI car would you change the stock dwell at the higher boost rpm's ?

[WS6FirebirdTA00]

What about an FI car would you change the stock dwell at the higher boost rpm's ?

Once again, as my posts say, NO do not change it higher it will not do anything but burn up the coil faster.

[INTHERED]

Once again, as my posts say, NO do not change it higher it will not do anything but burn up the coil faster.

The cars you tested on the dyno were they FI cars ?

The FI guys recommend reducing spark plug gap based on # of lbs of boost.

I was thinking maybe I could run a larger spark plug gap with increased dwell ?

[WS6FirebirdTA00]

I have tested this from stock cars to 700+ hp cars, NA, FI, nitrous, no power was gained.

[5_Liter_Eater]

I was going through my tune yesterday and noticed that it had some different spark dwell numbers than stock. When I got my car it had the cam, headers and tune alredy installed from a tuner that the previous owner went to. I came across this thread and have set them back to stock. Good info. Thanks!

[INTHERED]

I have tested this from stock cars to 700+ hp cars, NA, FI, nitrous, no power was gained.

What about in regards to making my car a little less knock sensitive ? It seems that my KR seems to be right on the ragged edge and if more dwell would help that would be OK

[WS6FirebirdTA00]

dwell is not going to help that from what I understand about it.