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There's a few reasons to keep the dwell short. Yes, the coil can get hot if it's constantly running at max dwell and that will reduce the lifespan of the coil. Constantly running max amps across the spark plug gap and the cap/rotor gap will also reduce their lifespan since a hot spark will erode the electrodes, plus it will oxidize the terminals in the cap and rotor, reducing their conductivity. But the engine needs more spark energy at peak torque since that's when the air/fuel charge is at it's greatest density, and it's hard to shoot a spark across the plug gap when the plug gap is full of low-conductivity air and fuel. So the stock DME has low dwell time at idle and low rpm to keep the coil cool and improve the durability of the ignition components while using higher dwell time at higher rpm to ensure a good spark and complete combustion at max power.
That seems to contradict the dwell map though. If you look at the map in my post above, it shows that the dwell time is slightly higher at idle, and then about the same all the way from ~2000rpm to the limit. The only significant increase in dwell time is for very low rpms which might be to compensate for the alternator and/or battery being already very heavily loaded while cranking.
That seems to contradict the dwell map though. If you look at the map in my post above, it shows that the dwell time is slightly higher at idle, and then about the same all the way from ~2000rpm to the limit. The only significant increase in dwell time is for very low rpms which might be to compensate for the alternator and/or battery being already very heavily loaded while cranking.
Your dwell map is odd. I'm not sure why it seems backwards. Every other standalone I've tuned has less dwell time at low rpm and more dwell as rpm goes up.
Here's my dwell time map. I modified the table by lowering most values since I have an MSD Blaster coil. These values are straight from the bin file, there's no conversion math applied in the xdf. Does your xdf have any conversion math? I know that lowering these values reduces dwell time since I tested the misfire threshold at idle by lowering the dwelltime until it misfired, then added back 20%. Modified Dwell Map
Your dwell map is odd. I'm not sure why it seems backwards. Every other standalone I've tuned has less dwell time at low rpm and more dwell as rpm goes up.
Here's my dwell time map. I modified the table by lowering most values since I have an MSD Blaster coil. These values are straight from the bin file, there's no conversion math applied in the xdf. Does your xdf have any conversion math? I know that lowering these values reduces dwell time since I tested the misfire threshold at idle by lowering the dwelltime until it misfired, then added back 20%. Modified Dwell Map
The dwell map I posted is one I found earlier in the thread, but before I posted it I double checked the values, and came to the conclusion that it was correct.
IIRC, the raw values are angular measurements. The map in my post shows the values converted into time (in ms). From my notes at the time:
for instance, for 800rpm and 14v I have the value 18.
Multiplying this by 1.363 (degrees per half-tooth) I get 24.54 degrees dwell time.
Now 800rpm is 75 milliseconds per rev, or 0.2ms per degree.
So that gives ~5.1ms dwell time.
So as rpm increases, the tooth count (i.e. angle) stored in the table has to get higher to maintain the same dwell time.
The dwell map I posted is one I found earlier in the thread, but before I posted it I double checked the values, and came to the conclusion that it was correct.
IIRC, the raw values are angular measurements. The map in my post shows the values converted into time (in ms). From my notes at the time:
So as rpm increases, the tooth count (i.e. angle) stored in the table has to get higher to maintain the same dwell time.
It's no wonder the Lindsey/Rogue xdf says " Don't change this table unless you know what you are doing!"
I checked the bin file and the values in the Rogue/Lindsey dwell map are the same as the stock table, so they didn't change the code or anything. They just changed the xdf so the table has different units.
Hey.....haven't been on here in a while....stumbled on this again.
Has there been a solid conclusion drawn on the merits of the MSD blaster coil vs the stock bosch unit?
Was the original information posted by Rogue tuning correct?
Hey.....haven't been on here in a while....stumbled on this again.
Has there been a solid conclusion drawn on the merits of the MSD blaster coil vs the stock bosch unit?
Was the original information posted by Rogue tuning correct?
No, the info about the how the MSD Blaster compares to the stock coil is mistaken. There's plenty of dwell time available to fully charge the stock coil all the way to the red line and beyond. I can't comment on the stuff about the other coils.
There's plenty of dwell time available to fully charge the stock coil all the way to the red line and beyond.
I'm being pretty lazy as this may have been answered in this thread already. How much time is needed to fully charge the coil? You gots 10ms at 6000 RPM.
I'm being pretty lazy as this may have been answered in this thread already. How much time is needed to fully charge the coil? You gots 10ms at 6000 RPM.
Thanks
Mike G.
Around 3.8ms in theory, but you can see from my post here that it's pretty close to the full current at anything above 3ms. If you look in the 14v range of the dwell map (in the same post) it shows 3.6ms dwell time for most of the range.
At 6krpm you actually have 5ms though, not 10ms - there are 2 ignition events per rpm.
No, the info about the how the MSD Blaster compares to the stock coil is mistaken. There's plenty of dwell time available to fully charge the stock coil all the way to the red line and beyond. I can't comment on the stuff about the other coils.
So, I too, can be quite lazy at times.......and especially when it comes to electrical, I don't feel like deeply learning this stuff and checking others info.
Back in the day Rogue was no dummy when it came to unlocking the intricate details of the DME and related components (ignition, in this case).
But, even the best in their fields can get it wrong sometimes.
So, where do you feel was Josh's error in this case?
If I remember, the bottom line was that the Blaster Coil, apparently, had significantly higher ignition energy available at the higher RPMs , as opposed to the stock coil. This was at the expense of a little more current running through the ignition components of the DME.
So, I too, can be quite lazy at times.......and especially when it comes to electrical, I don't feel like deeply learning this stuff and checking others info.
Back in the day Rogue was no dummy when it came to unlocking the intricate details of the DME and related components (ignition, in this case).
But, even the best in their fields can get it wrong sometimes.
So, where do you feel was Josh's error in this case?
If I remember, the bottom line was that the Blaster Coil, apparently, had significantly higher ignition energy available at the higher RPMs , as opposed to the stock coil. This was at the expense of a little more current running through the ignition components of the DME.
Well I explained the details in my original post, but in summary the claim was that there isn't enough dwell time above 4000rpm to fully charge the stock coil, and therefore the MSD coil is better, because it charges faster. Sound reasoning, but it's wrong because there is enough time to fully charge the stock coil, as I showed. Josh must have been testing with an unrealistically low voltage to get the results he got. This can be verified by looking at the charge current or independently by looking at the dwell time (which is set by the DME base on the voltage it measures).
My guess is he was using some kind of bench set up with an adjustable power supply and just had it set up wrong. Or maybe the test was done while cranking, in which case the DME will see low rpm and low voltage, and use very long dwell times to compensate.
The thing is, though, however he tested the stock coil....one would assume he tested the blaster coil the same way.
Then both coils would have been handicapped in the same way (low supply voltage, or whatever)....yet the blaster came up on top in the higher RPMs. (Actual numbers aside)
You see my reasoning here; or am I way off the mark.
Also, if the Blaster coil would cause higher current to run through the system/DME, etc, it's gotta show up somewhere, no?
The thing is, though, however he tested the stock coil....one would assume he tested the blaster coil the same way.
Then both coils would have been handicapped in the same way (low supply voltage, or whatever)....yet the blaster came up on top in the higher RPMs. (Actual numbers aside)
You see my reasoning here; or am I way off the mark.
Also, if the Blaster coil would cause higher current to run through the system/DME, etc, it's gotta show up somewhere, no?
Yes I presume both coils were tested under the same conditions. The point is that those conditions are unrealistic. There's no advantage to the Blaster coil if there's enough time to fully charge the stock coil. He thought there isn't enough time, but there is. That was my only criticism here - I'm sure everything else he said is fine.
07-15-2020, 10:08 PM
