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 MSD Chip Resistance 
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Joined: Fri Feb 08, 2013 5:50 pm
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Figured this might be a nice sticky here. Also an Excel file you can download is attached.

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MSD Chips.xlsx [59.05 KiB]
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Fri Apr 05, 2013 4:38 pm
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Joined: Fri Mar 22, 2013 6:23 pm
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Location: Newcastle, NSW, Australia
Thanks for that Mark! I had this somewhere before and lost it.

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Sat Apr 06, 2013 5:22 am
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Thanks... It is very interesting to test the actual RPM that the chips operate. Some will just go lazy a few hundred RPM before their cut off RPM others will run up to the rpm and chop down. I've often wondered what is the test or if MSD even tests them.


Sat Apr 06, 2013 11:16 am
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The actual resistance to RPM is a curve, and I imagine some resistors used are just the closest available standard and why they may be off a little. Variations in the analog circuity on the older boxes may account for a little as well, along with connection resistance from oxidized terminals. I used to build my own two steps, they were just a relay that selected one or the other resistance for the high and low side. I also used potentiometers, you could literally dial the exact RPM you wanted. With the new digital boxes it's all in the software.


Sat Apr 06, 2013 11:38 am
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Location: Newcastle, NSW, Australia
jmarkaudio wrote:
I used to build my own two steps, they were just a relay that selected one or the other resistance for the high and low side. I also used potentiometers, you could literally dial the exact RPM you wanted. With the new digital boxes it's all in the software.

Interesting you say that as I've been thinking of doing the same thing. . my car runs a digital 7 but dad's car still has a 7AL3 in it.
Is there any current as such in the chip circuit? Just wasn't sure if it would toast a potentiometer.
I'm assuming by looking at the size of the resistors inside an MSD chip they're only 1/4 watt or so. . so I can't see there'd be any reason a potentiometer wouldn't work?

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Sat Apr 06, 2013 6:50 pm
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No problem at all.


Sat Apr 06, 2013 7:33 pm
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A formula I found for this as well. Have fun with this one...

resistance (in ohms)=(-1*(10^-14)*(RPM^4))+(3*(10^-9)*(RPM^3))+(7*(10^-6)*(RPM^2))+(0.6371*RPM)-150


Tue Jul 09, 2013 9:01 pm
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