dwell ignition timing? Can someone explain this to me?

[98vtec]

I've done some research on this through wikipedia but can someone help explain this to me in laymans terms and not automotive jargon? What effects does this option in eCtune have? thanks in advance

[JaredKaragen]

Please google search \"What is Dwell Angle\" and \"What is Dwell timing\", also look in an automotive textbook to get more info; and start reading... sorry; hard to explain in simple words.... It changes the way your ignition fires in a sense; but dwell is the time that the coil is disconnected from the points in older setups... but EFI is a little different; slightly. I don't know if someone else will chime in here, but most users just leave the settings stock as the OEM ignition performs well with those settings in most cases.

[98vtec]

i'm only wondering in the case that these settings could possibly be tweaked to allow for better timing control with high compression motors on pump gas like my own. so from after getting a better idea, this dwell time is the amount of time the coil has to build up voltage until the time for it to be discharged, correct? I read that the coil charge may become weak in the event that the coil loses the ability to hold the charge at peak voltage. How can this voltage be measured to see if the coil is charging appropriately and not falling off before being discharged? If, hypothetically, the coil was not charging correctly during this dwell time, how can i determine by looking in the eCtune dwell tables what needs to be changed? I haven't seen much discussion on this topic in the tuning forums so it would be nice to have a tech topic regarding it. thanks for your reply jared.

[98vtec]

ok after reading some more, it appears that i need to purchase a dwell meter in order to get an idea of where i am at. the dwell meter will tell me the number of camshaft/distributor degrees that in rotates during the closed (voltage build up) stage, i understand this..... but how can i relate that information to the tables in eCtune?

[Adam Hopkins]

Some of you asked about what I did with the dwell table to help out with spark. A lot of what I'm going to discuss will make more sense with a scope. Dwell basics: -The signal from the ECU to ignitor essentially controls primary coil voltage. -There are two edges to the signal. -The falling edge is what you are used to manipulating, as the coil fires on this edge. -The rising edge controls when the coil starts charging. -The length of time between the rising edge (charging starts) and the falling edge (firing) is termed DWELL. *note* I may have my edges backwards, but the concepts will still work. Longer dwell periods mean the coil has longer to charge. This MAY mean that you get more spark energy. I say "MAY" as opposed to "WILL" because you reach a point of diminishing returns where the coil is saturated and cannot store more current. At this point, increased dwell will only contribute to thermal stress on the coil without increased spark energy. I managed to find the following information: All Internal Coils (Hitachi & TEC) Average Maximum Current Flow: 5.5 – 7.5 amps Total Dwell Time: 3.6 - 4.1 ms Ramp Slope: 1.7 – 2.0 amps per ms All External Coils (TEC) Average Maximum Current Flow: 6.75 – 8.75 amps Total Dwell Time: 3.6 – 4.1 ms Ramp Slope: 1.5-2.5 amps per ms From my experimentation with the dwell control table available in eCtune, I suspect highly that it is a dwell adder table. The ECU calculates some form of base dwell value (in degrees of crank rotation) and this table is used to add degrees based on RPM in order to (presumably) provide increased spark energy at higher RPMs where it is most needed without heating the coil unnecessarily at lower RPMs where the extreme spark energy is not so important. I took the 11,000 RPM dwell value out to 25 units and noticed quite a marked difference in breakup. I tried to increase other values minimally. Beyond that, I can't tell you much. I edited it as a last resort, and would recommend staying away from it whenever possible. -Dave

I hope Dave dose not mind me sharing, Then again he did start pgmfi.org, so I do not think sharing is a problem for him.

[98vtec]

so he recommends leaving it alone. Hmm. Only thing i see a little confusing is his wording of the tables only being adders. I understand what he is trying to say, but you can reduce the \"stock\" RPM advanced table and in a sense not make it sound like you can only add advance to that particular table. Is it plausible to say that you could reduce the voltage charge from the coil to run a more aggressive table timing advance but theoretically less of a chance for detonation/pinging, etc?

[JaredKaragen]

I would figure the only reason would be to tune in the coil your using to obtain a higher RPM spark that is consistant; when plug gap is not helping.... but it is really fine to leave as-is under pretty much all circumstances.

[98vtec]

I figure if the coil is \"tuned\", that you could do more with a high compression motor running pump gas, like my own. Possibly create a larger window for error.

[Bugermass]

I have tuned quite a few high compression motors on puimp gas, and the dwell tables arn't really going to make much difference. What I dicovered from some brave testing ( holding a timming light during WOT pulls on a dyno) is that the \"Dwell Rpm Ignition Advance Base\" will actually cause timing to float upwards. Initially we were seeing increase of 6 deg from table timing when the 11,000RPM value was set to 26. I believe the reason there was less breakup on top end was due to the added timing that this particular table was adding. It was changed back to the values its at now since this give the least amount of timing float from the table values (less than 1 deg or so). As far as \"Dwell Rpm\" and \"Dwell Battery\", I have not been able to fully test and prove definatly what these values do. I'm not aware that any of the other ectune tuners have either.. This is somthing that eventually needs to be tested and its effects proven, so we know for sure what they do.. In your case though I don't think theres much to gain from messing with these tables.

[98vtec]

thanks chris. i sent a message to don flores to ask him his thoughts and i got roughly the same answers. 98vtec (2:36 PM 8/19/2008): hey what is your opinion on changing the ignition dwell through programs like eCtune? Does DTA have this option? Have you found any benefits from adjusting this with high compression motors on pump gas like my own? DonF (3:34 PM 8/19/2008): We played with that long ago. Too much spark and dwell lost us BHP. That was a llong time ago when I bringing a new ignition system to Petty's, Yates, Loynings, etc. The DTA does move it around but i have not done much latly. 98vtec (12:12 AM 8/20/2008): was the loss significant? I'm searching for information regarding this feature and i have a pretty good idea about the concept of ignition dwell but i am unsure on how to determine whether the coil is charging at the optimal voltage. any thoughts? Do you know the correct ratio off for charging and not charging? I believe i read somewhere that its a 200:1 ratio. so 12volts would be 2400 volts at full charge.... DonF (1:21 PM 8/20/2008): That numer I am not sure of, have to back to E=IR. With the DTA we set the coil on time between 1000-5000 Micro Seconds. 3000 seems to be the number of choice. The external coil amps determine the number, I just use Alan's chart, as he used to design missle software, I trust the Rocket Scientist over me. When I went around the country to test this new ignition system that had more voltage and dwell we lost power at every shop. Only until we backed down the numbers to a MSD unit were we the same. A good idea gone bad. They actually designed this for \"lean-burn\" engines, but when that market did not happen, they hoped the performance market would, it did not. I could buy a MSD box cheaper than the parts they had in the box.

[xenocron]

I would theorize that tweaking the dwell tables might only be useful if using an after-market coil like MSD or whatever. I would guess that the stock coil tables could be tweaked to help these coils with the typical problems that are experienced in weak spark or quick failing coils.