My OE coils solved my issue, just hope the BHR ones don't bring it back.

Covering Dwell
 

Seems the more I search the more questions I am encountering, and I realize I will be harassed for this but my understanding is not what I would like it to be before I feel comfortable enough to make a change so.

Questions,

1) OE dwell is approx 3.5ms

2) BHR kit D585 coils is approx 5ms

3) I understand some call it a day and go with M=1.45, which seems to do well for the lower RPM's but leaves anything above 6K still on the low side.

Now ideally you want the coil to have 5ms between fires to charge up, the most dominant chart people seem to use
http://imageshack.us/a/img853/3103/psl8.jpg

Realistically we are really only concerned with 12.75-14.00 volts range as that is the operational range for the vehicle, so why on the table are the lower voltage values in the 20ms for dwell time?

I guess my main question being is if the coil has an optimal dwell time of 5ms, why not change every RPM to 5ms?

Using ATR, taking the chart and multiplying by .004 results in the dwell time that is currently set you can see that the OE dwell pushes the coils above 3.5ms for most of the low RPM band not sure why a manufacturer would tune knowing they are directly damaging the components.

I know I am reiterating a lot that has been discussed before, but if I am misinterpreting anything feel free to let me know.

It appears that oltmanns Table is the most popularly used, I am not understanding why putting the table at a flat dwell of 5ms is not the best result.

Dwell relates to the amount of charge time the coil is allowed to have.

That is very dependant on the amount of voltage the coil receives. The amount of charge the coil gets at 5ms at 11.0V is much different than 5ms at 14.0V

What is important is the coil gets enough charge to fire properly.....and not too much, because the extra will be converted to heat and the coils will fail prematurely

Coils are designed with different parameters....and available dwell time is one of them. Coils that fire often like on 2 stroke high rpm engines are designed to charge with short dwell times...because the available time between coil firings is very short at high rpms

On sequentiall firing V8's there is much more time between firing incidences...even at max rpms....

Anyways.....not sure if that helped ;)

^ fantastic explanation. Perfect balance of 'laymans' terms and technical data.

That did help with my basic understanding of dwell and its effects on coils for their different needs.

My basic question is simply why is a flat 5ms dwell table not the best option, even at 9KRPM the coils have 6.6ms between firs and I believe a ms recharge rate. So why wouldn't a flat 4-5ms dwell chart be optimal for D585 coils?

There isn't any reason not to at normal operating voltage.....That's what I run in my application

You don't have 6.6ms though at full rpm...there are some latencies that give you less in the real world

The other thing...is that the Yukon coils are charge limited internally...so they shouldn't overcharge and burn up :)

The chart Oltman produced was based on the OEM settings for those coils . I guess the manufacturer gave those settings as optimum for enough spark vs longevity of the coil.

My basis was that for 12.75-14.00V (normal) operation to produce a dwell from 5ms at 1KRPM and taper down to 4.5ms at 9KRPM and leave the rest of the chart alone, seems the most logical and the most optimal for these coils anything else at least to me seems like you upgraded you mechanical parts just to limit them by the electrical configuration.


Based on what OEM settings? M-1.45 would be a linear base of the OEM, Oltman chart was not a linear change,

Based on GM OEM, Mazda OEM, please clarify.

I think (from memory) he got the settings from a vehicle that used those particular coils .

FWIW i noticed a marked improvement in startup on my car when i changed to those settings . I strognly suspect that the 5398 setting is the one used by the ECU for startup dwell.
Which is why i rabbit on so much about how the 585 coils on stock startup dwell (of 1895) are inferior to stock coils.

Where did you get the 3.5ms settings? I am guessing the Field Service manual. Recheck what it says. Use an oscilloscope to verify 3.5ms at idle to ensure the coils are functioning properly. It doesn't say 3.5ms all the time.

We don't drive on startup dwell, not seeing it as a big deal.

For all else reading this post I raise you the question.

If D585 coils have a built in charge capacity limitation, why would you not just max out the entire table? Seems logical. The coil will limit itself to 5-5.5ms.

Well you aren't the guy that is having problems starting your car .......... so i guess you wouldn't ;)

Anyone have an iterpretation for this, came straight from COBB

Ignition Dwell Time
Table description – This 3 dimensional look-up table indicates the desired ignition coil dwell in milliseconds (1000mS = 1 second). The horizontal X-axis breakpoints are defined by engine speed (RPM) and the vertical Y-axis breakpoints are defined by battery voltage. The values in the table represent the amount of ignition coil charge time under different engine RPM and voltage conditions. All ignition coils require a certain amount of charge time before the full spark energy can be discharged, this is referred to as Ignition Dwell. This property may also be referred to as coil dead time or dwell time. The amount of latency a coil needs depends on the design of the coil and the spark energy necessary to ignite the combustion gases. Lower battery voltage will increase the coil's dwell (dead time). Likewise, higher battery voltage may reduce the charge time necessary. The factory ECU has ignition dwell adjustments based on battery voltage and engine RPM. The data in this table is represented in milliseconds; this is the only table that exists for the sole purpose of adjusting ignition coil dwell values.

If this is correct, than the OE dwell table is severely low. At which case the entire table just needs to be filled with 5000 to make a 5ms dwell time.

That description is .................................................. .........................................WRONG ! The number in the table needs to be divided by 256 to give you mS .

There is a lot of forum history around this subject . A certain prominent individual had the entire community believing (except myself and a few others) that the table had something mystical about it which only he understood. The truth only came to light sometime after that member was banned .

Since then a lot of tall tales introduced by that same ex-member have been debunked .

How do we know oltmanns conversion is correct? has anyone measured it?

I would think that we are talking computer time, meaning Period. T=1/P

Meaning the OE chart at 1000rpm/14v=1105 and 9000rpm/14=395

Then that would yeild 1/1105=.9ms and 1/395=2.53ms

Thusly the chart dwell is increasing with RPM not decreasing.

Assuming it is an 8-bit binary derivative without proof does not prove that other conversions are wrong.

oh boy .
Have you read the infamous 'Dwell' thread ?

You really should - many hours of reading and hilarious entertainment . All the answers you seek are contained therein.

https://www.rx8club.com/series-i-eng...ighlight=dwell


In particular THIS PAGE :

https://www.rx8club.com/series-i-eng...-178635/page5/

I skimmed it today, didn't have the time to read all 12 pages, was going to finish it tomorrow. I realize what I am saying has undoubtedly already been questioned. I just have not seen where anyone has gone and measured the dwell at a voltage and RPM and given the exact conversion for the table.

It still seems to me that with the D585 coils that going through all this conversion is useless. Max out the table and let the coils monitor themselves for dwell.

I am still not seeing why this is a bad idea? :dunno:

Maybe ............... a huge spark at certain rev ranges is just overkill and they want to save the spark plugs from premature wear
Or ......... the device that prevents overcharging of the coil is only a safety backup and not meant to be utilised ALL the time .
:dunno:

Well I have the 1.45 advance on my current map ( this was before I read the thread today) and I notice that the throttle response is much better, and a much stronger idle, but over 4K RPM it still seems weak. I believe this generic multiplier could be improved upon in the upper RPM band.

I will do more research tomorrow and adjust accordingly, might see if I can borrow my buddies scope and get some readings this weekend.

I run 13-14 psi boost at 8000 rpm on the above dwell table (actually a combination of that one and the one Team posted) - you don't think that is a good test ?

Its attributed results, but you are also FI and run a much larger gap then I do which I think would factor. Im just throwing out my questions and thoughts. I know I am years later than the testing and discover of the appropriate tables just trying to figure it out in my own way.

Any chance you could throw your hybrid table here, I know team was running a flat table a while back, not sure if he still is.

Nope - just BUR9EQP plugs


Sure ............


https://www.rx8club.com/attachment.p...1&d=1378263810

I run stock plugs and am NA/ported. With the same table as brettus

I am running stock trailing plugs with no change in gap in both the leading and trailing positions with zero issues on the dwell table Team posted. I am turbocharged as well (in case you didn't know) and I can hit about 12psi depending on which gauge you believe.

Your boosted? since when? :lol:

Updated my table this morning, decided to run a flat 4.8ms dwell.

No issues so far.