Battery compensation tables, specifically coil dwell table

[Simon P.]

Are any of you guys using the coil on time table in the Battery Compensations tables? Coil on time = coil dwell, but unless you specifically check the box to activate it the tune reverts to the value entered in the General Engine Settings and uses that value across the whole voltage range.
So, with DTA giving us sooo much information on how to use and choose these parameters (taken from the S100 manual):
COIL ON TIME
This is the length of time the coil is turned on before firing (also referred to as the dwell time). This allows changes to suit different coils. Most coils require 2000 - 3000 micro seconds so unless you have specific information from the manufacturer of the coil leave this alone.
BATTERY COMPENSATIONS
Windows menu:- Other Map Settings/Battery Compensations
Assuming information is available from your manufacture of coils and injectors this function can be filled out and used. Such information is not easy to obtain in a lot of cases. The table is self explanatory.

I'm just wondering if others have used the dwell table to adjust low RPM (low voltage) vs high RPM (high voltage) dwell and what general parameters were chosen other than "Most coils require 2000 - 3000 micro seconds so unless you have specific information from the manufacturer of the coil leave this alone. " which is a little disapointing to read when one of the purposes of using a stand alone EMS is the possibility to not "leave this alone"...

[ignitionautosport]

unless you have the data specific for your coils vs voltage, don't use it. Basically.

If you have enough knowledge without this info to make an educated guess, then of course go for it.


hang on, I just re-read that. High rpm doesn't necessarily equal high voltage. your regulator should take care of that and keep it fairly constant.
This table is for those situations where your alternator may die and you want the car to keep running successfully till the end of the race, so increasing dwell will give a similar spark at lower voltages. Or if it starts overcharging it can back dwell off so as not to fry your coils. Some cars don't always charge correctly at idle due to alternator gearing for higher rpm operation so it helps then too - though injector dead time table more so. And on cranking more dwell can help as the voltage drops due to turning the starter/engine over.

[stevieturbo]

The leave it alone unless you know otherwise is a very valid comment.

If you knew better, you wouldnt even be raising the question !! The fact you are means you dont understand the consequences of entering the wrong ( ie too high ) a value. Which can of course either fry your coils, or the coil drivers.


And back to the first comment, if you dont know what any aspects are for and the car is running fine. I'd have a big red warning everywhere to leave it alone lol

And as above, you seem to have a notion that voltage changes with rpm. Certainly on any car Ive ever worked at it does not.

dwell vs boost or rpm would be a nice feature though.

[Simon P.]

Alright, so I guess my understanding of this function was a bit skewed. I was under the impression that this function was to adjust dwell vs RPM but that DTA had chosen voltage as the variable relating to RPM, which did seem odd...
And yes Stevie, dwell vs RPM or boost would be a nice feature, that's actually what I thought this was but I get it now that this function is totally different.
I still think the leave it alone thing is borderline insulting. I mean sure, not everyone has the ability or need to use all the functions available correctly but a bit of explaining like ignitionautosport did goes a long way.

[86sixsix]

a big kajonga +1 from me on 3d dwell if anyone talks to the powers that be...i asked but that's as far as it went

yeah this is purely to keep a motor going 'properly' as long as possible with no recharge system (for whatever reason)

[DTAS54]

The leave it alone unless you know otherwise is a very valid comment.

If you knew better, you wouldnt even be raising the question !! The fact you are means you dont understand the consequences of entering the wrong ( ie too high ) a value. Which can of course either fry your coils, or the coil drivers.

And back to the first comment, if you dont know what any aspects are for and the car is running fine. I'd have a big red warning everywhere to leave it alone lol

And as above, you seem to have a notion that voltage changes with rpm. Certainly on any car Ive ever worked at it does not.

Steve, with all due respect, a lot of people come here to "learn otherwise", so telling some one to leave it alone if you don't know something is a pretty generic insult. How would you feel if a question you asked was greeted by, "if you have to ask, you are not meant to benefit from the knowledge, don't bother with the subject"

Actually, you are wrong. The "fact" that he asked about this topic most certainly doesn't imply he was ignorant of the risks. In fact, as it happens I know Simon, and in conversations we had prior to his posting on this, we discussed and knew the risks....but were having a struggle finding data sheets for our coils....hence, our wondering if anyone was using these tables....and hoping to open an educational dialogue on the subject.

Your experience is invaluable. But it may also be limited to electrical systems running stock crank and alternator pulley systems with heavy duty batteries. A track car optimized for weight with a tiny battery and a virtually unstreetable set of pullies that will be fine between 4000 and 8000 rpm might not give you a stable voltage at idle or lower rpm. (of course you could argue don't use those pullies)

A cursory look at some Bosch data sheets makes it pretty clear that their coils do in fact have varied specs for different voltages.

So perhaps an intelligent response back to Simon might have been...."What voltage swings are you seeing during normal operation that make you think you would benefit from using this table"

From looking at the spec sheets, it appears that utilizing this table is a great idea if one has access to the right data. I'd bet OEM computers do this...

[stevieturbo]

TBH if you have an unstable electrical system, then you need to rectify that. There is more powered by electrics than just the coils. So why would you take risks ?
Lightweight is all good and well, but if it then poses a danger to the engine, is it really a smart move ?
Ive heard of other guys running lightweight alternators etc, and they seem to have a high failure rate. Surely a few extra kg's on a critical component for peace of mind is worth it ?
Or just buy a better specced lightweight alternator in the first place
A rock solid power supply is essential to any car IMO. Some people even use voltage regulated supplies on race cars to ensure it stays at 14v regardless, or else it all just stops.
Perhaps something worth considering, although it would add a little weight.

And if he understands the risks, then he should also understand to ignore the warning so it really is a non-issue.

But regardless of dwell time used. No amount of dwell will increase spark performance if the battery voltage is woefully low. Compensations only go so far.

The OEM do a lot of things far and beyond what DTA do. They also spend millions developing them, and no real need for warnings as neither you nor I can easily access their computers.
And the only true way to discover optimal on time for your coils would be to measure it, and see at what dwell current draw flatlines during charging.
Although if voltages are unstable, this might make that difficult too ?

Here are some graphs I found online with various coil info from testing. Although these results dont seem to tally up with what some coil sellers claim.

http://picasaweb.google.com/10605881916 ... itionCoils#

[Simon P.]

Edited as per DTAS54 request.

My own car idles around 1150RPM and actually can't recharge at that speed as the alternator ouput voltage is around 11V. There's nothing the regulator can do about that. Using the compensation table could help me here. Obviously what little time I spend idling I try and not use too many accessories. The cooling fan is actually all that I run at idle and even it's on a thermostat so not constantly running. Although I can't be 100% sure I think adjusting dwell based on my voltage range (11V idling, 12V at 1300RPM, etc) could help smooth out my idle enough to be felt. Running a fixed dwell may well work fine if your voltage regulator is doing it's job throughout your RPM range but as mentioned this isn't always the case.
As far as getting the right dwell values for a specific coil, this has been the most frustrating part of all this. I certainly understand the implications of enterring unrealistic values in the dwell table. Too long a dwell period may well overheat the coil. Most coil drivers are clamped and will self protect at a defined max current but since I have no idea what drivers DTA uses and what the clamping current is I certainly don't want to experiment. Burning coils is also not an option for the same reasons.
Steve; thanks for the link to all these coil dwell tables. Unfortunatly, Bosch 1221504464 (could also be 0221504100) is not in there. We did find quite a bit of info directly on the Bosch Motorsport web site but nothig specific to the above mentioned coil. One interrsting note is that on Bosch coils which did have published dwell values and whose part# closely matched ours the dwell times were ridiculously low at 14V. Like in the 1.2 to 1.4ms range. Quite a bit lower than what DTA suggests in the manual.
If anyone has specific info on the BMW/Bosch coil # listed above, I'd love it if you shared. Right now though, we're thinking of using the close Bosch coil info to move forward with this.

[VR6Turbo]

Below is my compensation table. I've used it on 3 different engines now with success. I've always used Bosch coils but obviously I change the injector dead times (Paul Yaw over at Injector Dynamics does them for me) for each appliction accordingly.

I predominantly use VW engines and I know from looking at the factory maps that they vary the dwell against load & voltage, in the range of 2 - 4ms, so I just copy what they do.

[Simon P.]

Thanks for your table, it seems to be very much like what I'm looking to do. One question though, are these engines you mention all COP are do they use coil packs? From doing a bit of reading COP dwell times are much shorter than coil pack dwell times. Like 50% shorter...
Paul Yaw's a nice guy, I know him from http://www.yawpower.com, his rotary past. Never met him personnaly but he's got a lot of credibility as a tuner/fabricator.