As some of you know, the last couple months I have been helping reverse-engineer the BMW ignition system in order to help develop a path for upgrading it. The stock system isn't horrible, but it has many shortcomings as everybody who owns a high powered N54 is well aware of. That being said, since others seem to also be developing upgrades, I think I'll start releasing some information on what I've found for the benefit of the community. Unlike some other threads, this is all new information, and will be expanded and refined the next 1-2 months as testing continues.
1) What are the hardware limitations of the DME? We'll use the older MSD80 to expand on this question. If the hardware is good, it opens up different options than if the hardware is lacking to begin with.
Nearly all BMW's use TCI systems for spark (transistorized coil ignition), which means they have a transistor IGBT (also known as an ignitor) to drive an inductive coil. The transitor is located inside the DME, as opposed to some cars which have a module. The transitor used is a Fairchild ISL9V5036S3ST class IGBT, the datasheet can be downloaded here. It's a very nice transistor, capable of over 30 amps per channel and 250W heat dissipation, among other key features.
The way the circuit functions, is you have a 5v logic signal to the IGBT in the DME. That grounds an output to the coil, energizing the coil (coil has constant 12v and a secondary ground in addition to the coil - signal). When the 5v logic signal ends, the ground path ends, and the coil fires. This is a "dumb" system since the transistor (aka ignitor/IGBT) is separate from the coil. Basically, the transistors function as the points in an old muscle car. Smart coils (LS, Audi, Honda) have the 5v logic going straight to the coilpack, which has the IGBT incorporated.
2) What are the current ignition coils capable of? Bosch/Delphi OEM coils were used to establish a baseline, to see just how powerful the factory system is, and what the limits are for dwell time.
The best way to test an ignition coil is with an oscilloscope. There are a few key things to be concerned with including primary coil amperage draw vs dwell time, primary coil saturation point, secondary coil peak voltage potential, and secondary coil output. Some of these measurements are more difficult to obtain that others. Here are some of my results that might be relevant to everybody on the platform for OEM coils (as always I encourage others to independently verify this but I'm confident in these results):
a: Bench testing OEM coils. Top trace (green) is function generator signal (dwell), yellow is current draw, lower trace is high tension (secondary voltage, spark starts when primary current collapses and ends at the squiggly, better seen in lower image with upgraded coils)
b: Testing OEM coils on a running car. Current draw can vary based on operating conditions but is a quick and easy way to see if the tables in the XDF are functioning as expected. In a nut shell, at the beginning of this project, they were not. Now they are, and similar to the bench testing the coils saturate around 3mS at ~14V. Note- current clamp was being finicky today and no good secondary coil data due to technical difficulties with interference (no spark plug wires makes it difficult to obtain):
If you want to know the mJ output of the Bosch, it's low. The DME can handle more amperage than this, the coils were simply saturating. More will be released on this later.
Just for fun, here's what an upgraded coil looks like on the test bench at 1, 2 and 3mS with significantly stronger secondary output:
3) Is the DME hardware limited by software? Just because the hardware is good, doesn't mean BMW won't stop your fun.
Some of us have tested the Dwell table before and found that the car did not react as expected. Some of these people have voiced concerned that despite the new tables we still do not have proper dwell control with the DME. I feel my results here are compelling. Regardless. Working with Jake and MHD, the Dwell table appears fully functional and at least one cause of current limiting has been resolved.
Lol
4) Which coils should be considered for upgrades?
The answer is always LS swap, for everything car related. Except LS are smart coils and tend to discharge early if over driven. Price, reliability, power are the players. I would love to hear opinions on what would constitute the best coil for these cars, as it seems there's a few drastically different versions coming out in the next 1-2 months.
1) What are the hardware limitations of the DME? We'll use the older MSD80 to expand on this question. If the hardware is good, it opens up different options than if the hardware is lacking to begin with.
Nearly all BMW's use TCI systems for spark (transistorized coil ignition), which means they have a transistor IGBT (also known as an ignitor) to drive an inductive coil. The transitor is located inside the DME, as opposed to some cars which have a module. The transitor used is a Fairchild ISL9V5036S3ST class IGBT, the datasheet can be downloaded here. It's a very nice transistor, capable of over 30 amps per channel and 250W heat dissipation, among other key features.
The way the circuit functions, is you have a 5v logic signal to the IGBT in the DME. That grounds an output to the coil, energizing the coil (coil has constant 12v and a secondary ground in addition to the coil - signal). When the 5v logic signal ends, the ground path ends, and the coil fires. This is a "dumb" system since the transistor (aka ignitor/IGBT) is separate from the coil. Basically, the transistors function as the points in an old muscle car. Smart coils (LS, Audi, Honda) have the 5v logic going straight to the coilpack, which has the IGBT incorporated.
2) What are the current ignition coils capable of? Bosch/Delphi OEM coils were used to establish a baseline, to see just how powerful the factory system is, and what the limits are for dwell time.
The best way to test an ignition coil is with an oscilloscope. There are a few key things to be concerned with including primary coil amperage draw vs dwell time, primary coil saturation point, secondary coil peak voltage potential, and secondary coil output. Some of these measurements are more difficult to obtain that others. Here are some of my results that might be relevant to everybody on the platform for OEM coils (as always I encourage others to independently verify this but I'm confident in these results):
a: Bench testing OEM coils. Top trace (green) is function generator signal (dwell), yellow is current draw, lower trace is high tension (secondary voltage, spark starts when primary current collapses and ends at the squiggly, better seen in lower image with upgraded coils)
b: Testing OEM coils on a running car. Current draw can vary based on operating conditions but is a quick and easy way to see if the tables in the XDF are functioning as expected. In a nut shell, at the beginning of this project, they were not. Now they are, and similar to the bench testing the coils saturate around 3mS at ~14V. Note- current clamp was being finicky today and no good secondary coil data due to technical difficulties with interference (no spark plug wires makes it difficult to obtain):
If you want to know the mJ output of the Bosch, it's low. The DME can handle more amperage than this, the coils were simply saturating. More will be released on this later.
Just for fun, here's what an upgraded coil looks like on the test bench at 1, 2 and 3mS with significantly stronger secondary output:
3) Is the DME hardware limited by software? Just because the hardware is good, doesn't mean BMW won't stop your fun.
Some of us have tested the Dwell table before and found that the car did not react as expected. Some of these people have voiced concerned that despite the new tables we still do not have proper dwell control with the DME. I feel my results here are compelling. Regardless. Working with Jake and MHD, the Dwell table appears fully functional and at least one cause of current limiting has been resolved.
Lol
4) Which coils should be considered for upgrades?
The answer is always LS swap, for everything car related. Except LS are smart coils and tend to discharge early if over driven. Price, reliability, power are the players. I would love to hear opinions on what would constitute the best coil for these cars, as it seems there's a few drastically different versions coming out in the next 1-2 months.
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