LS2 truck coil upgrade

[hungryjoseph]

I plan on doing this upgrade fairly soon, I'm almost ready to buy the parts. The factory RB25 ecu doesn't set the dwell time long enough for the Lsx coil to fully charge. For the Ls2 truck coils at 12 volts, the dwell time is 5.5 ms and increasing with respect to drop in voltage and decreasing with respect to increase in voltage. I found some chart that shows this relation for the LS2 truck coil. So the question I want to ask you guys is

1. When I look up dwell time adjustments, why does RPM make a difference (besides the extra voltage from a faster spinning alternator)? From what I've gathered, at 12V, the dwell time is 5.5 ms and the discharge time is 2 ms which means the maximum frequency is 133Hz which equates to 8000 RPM. BUT a spark in a cylinder occurs once every -TWO- RPM. Meaning at 8000 RPM, the spark is occurring at a frequency of 4000 times per minute. So theoretically (at 12 volts) you could spin the motor to 16,000 RPM before any adjustment needs to be made to the dwell time due to the motor frequency. Of course, at higher RPMs the coilpacks will see a higher voltage meaning the maximum theoretical RPM of the coilpacks is now even higher. Am I going wrong somewhere in my logic? I'm assuming there must be a reason people adjust for both RPM and voltage. I hope I was clear... lol.

2. Assuming everything I said above is right, I want to get an arduino board (http://www.arduino.cc/) and code i(30$t so that when it sees a digital input, it will hold a digital output for -X- ms as a function of -Y- voltage. Meaning if the voltage is 12, it will hold a digital output (5V) for 5 ms to the coilpack, essentially creating a longer dwell time. These boards are cheap, 30$ to 100$, and can take multiple digital inputs and outputs, including analog. I also plan on using this for reading my pressures, temperatures, and RPM but that's for another thread. Any comments or suggestions for this idea?

The reason I want to do this upgrade is because my motor breaks up around 4000rpm on stock boost and stock injectors. Yes, I have the correct spark plugs and gap. It might be the MAF? No boost leaks. Compression is good. Timing is good.

thanks for any input.

[Darius]

The ecu controls dwell. The LSx coils can handle up to 5 ms before additional dwell does nothing more than add heat to them. You can install them on a stock RB and they will run perfectly fine. Where have you read that you have to modify the dwell to get these coils to work?

[hungryjoseph]

I don't think I explained myself very well, sorry about that.

I didn't say the upgrade wouldn't work, and I understand the ECU controls dwell. That's sort of the problem here. I'm trying to program a micro-controller to get the full benefits of the upgrade by prolonging the 2ms dwell from the ECU to 5ms or whatever it needs to be depending on the voltage. Maybe I could keep it a constant 5.5ms and have a voltage regulator going to the power supply of the coils.

My main question is why do people adjust the dwell per both RPM and voltage rather than just voltage alone?

[Darius]

Ahh, I see. Good idea. I don't know the answer to your question though. Every tuning system I have seen tapers the dwell off at lower RPM and increases it up top. Maybe the OEM's are trying to save on wear and tear when the coils aren't needed to be firing against boost pressure and fuel.??

[hungryjoseph]

What I've seen is that dwell time is decreased at higher RPM's... It was some GM map I saw somewhere I have it saved on my other computer, maybe I could post it up when I get home. At first I thought it was because of the high frequency of the motor spinning but then I did the math and realized that doesn't really cause a problem for the dwell.

[hungryjoseph]

I just bought a set of used 8 on ebay with the connectors. I'm going to order the micro-controller next and next week we'll see how this goes.