I would like to put a comprehensive list together of the values for different RPM chips. ie: MSD's rpm chips.Since all RPM modules are based off resistance (ohms) all we need to do is use an ohm meter to read the resistance for a given RPM chip. Example only 2000 RPM=1.34 ohms. If we know the values of a given RPM it would make it easier for anyone with an adjustable module ( one with a small set screw you turn to increase or decrease the resistance) to tune without having to install and test in the car. You could also go to radioshack and buy the resistor and make your own. We could put this in the Tech archives for future use. What do you all think? I will put the list together if you guys/gals send me the resistance values for the following RPM's or anything in between.

3000=1.91 ohms
3200=
3400=2.21 ohms
3600
3800
4000=2.70 ohms
4200
4400
4600=3.21 ohms
4800
5000=3.58 ohms
5200=3.77 ohms
5400=3.95 ohms
5600=4.16 ohms
5800=4.35 ohms
6000=4.57 ohms
6300=4.88 ohms
6500=5.10 ohms
6600=5.20 ohms
6700=5.32 ohms
6800=5.43 ohms
6900=5.55 ohms
7000=5.65 ohms
7400=6.12 ohms
7600=6.38 ohms
7800=6.63 ohms
8000=6.89 ohms
8600=7.69 ohms
8800=7.97 ohms
9000=8.27 ohms

It sounds good to me. I would use the list to check my chips. I wonder if you would have a problum using a radio shack resistor. a gold line resistor may be neaded for accuracy. WB2IAS

Terry, here is a list I found on dragraceresults.com tech talk board a while back. When I checked my chips against it, they matched. Congratulations on your track outing by the way!!

3000 1.91
3400 2.21
4000 2.70
4600 3.21
5000 3.58
5200 3.77
5400 3.95
5600 4.16
5800 4.35
6000 4.57
6300 4.88
6500 5.10
6600 5.20
6700 5.32
6800 5.43
6900 5.55
7000 5.65
7400 6.12
7600 6.38
7800 6.63
8000 6.89
8600 7.69
8800 7.97
9000 8.27

Thanks Craig this is a great start. Maybe we can fill in the other numbers.

TC

I have some numbers written down in my trailer. I'll post them if they're different rpm's than Craig shows. Great question. I asked MSD if they had a list of them and it was like I was asking to date his eight year old daughter. He didn't even want to admit that such a thing existed! They'd like you to think that there's some mysterious circuitry in there.

I agree B1Ken I went through the same thing. Plus I think the price of there chips is alittle high. This should also help us troubleshoot suspected chip problems by simply taking them out and reading the resistance. I'd like to get values foe some of the middle rpm ranges ie:

3200
3600
3800
4200
4400
4800

I have edited my original post to include Craig's values.
I would like to fill in the blanks. THANKS

TC

Okay - first of all you are off by a factor of 1000. The values listed would be in kilo ohms. The values (at least in the lower ranges) appear to be pretty accurate.

Remember that if you are going to use resistors you want wire wound precision resistors. Carbon resistors vary too much with temperature and have a wide tolerance range (up to 10%).

I use a 10 turn pot for my launch rpm. I forgot if it is a 5k or 10k pot. I put a resistor in parallel with it. Forgot the value right now, but if the pot were to fail the rpm would still be pretty safe.

Below is the chart I use for my setup:

RPM setting resistance (ohms)
2000 100 859
2100 117 956
2200 133 1052
2300 150 1149
2400 167 1246
2500 188 1342
2600 208 1439
2700 229 1536
2800 253 1632
2900 278 1729
3000 300 1826
3100 333 1922
3200 362 2019
3300 397 2115
3400 433 2212
3500 470 2309
3600 515 2405
3700 560 2502
3800 611 2599
3900 670 2695
4000 733 2792
4100 803 2889
4200 880 2985
4300 970 3082

BTW, the MSD chips tend not to be too accurate. The 3000 chip I used to use went to 3100.

Well for anyone who cares, I did a 4th order polynomial linear regression of the values you provided. Came up with an R squared value of 1 (very good). Don't worry if you aren't a math whiz. The formula is pretty accurate from what I can tell given the resistance values you posted.

Bottom line is that you can use the following formula for any rpm you want:

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

or use the following chart:

rpm resistance
1000 497
1100 563
1200 630
1300 697
1400 764
1500 831
1600 900
1700 968
1800 1037
1900 1106
2000 1176
2100 1246
2200 1317
2300 1389
2400 1461
2500 1533
2600 1606
2700 1680
2800 1754
2900 1829
3000 1904
3100 1981
3200 2058
3300 2135
3400 2214
3500 2293
3600 2373
3700 2453
3800 2535
3900 2617
4000 2700
4100 2784
4200 2868
4300 2954
4400 3041
4500 3128
4600 3216
4700 3306
4800 3396
4900 3487
5000 3579
5100 3672
5200 3767
5300 3862
5400 3958
5500 4056
5600 4154
5700 4254
5800 4355
5900 4457
6000 4560
6100 4664
6200 4769
6300 4876
6400 4984
6500 5093
6600 5203
6700 5315
6800 5428
6900 5542
7000 5658
7100 5775
7200 5893
7300 6013
7400 6134
7500 6256
7600 6380
7700 6505
7800 6632
7900 6760
8000 6890
8100 7021
8200 7154
8300 7288
8400 7424
8500 7561
8600 7700
8700 7841
8800 7983
8900 8127
9000 8272
9100 8419
9200 8568
9300 8719
9400 8871
9500 9025
9600 9181
9700 9338
9800 9497
9900 9658
10000 9821

I can email an Excel spreadsheet with the formula to anyone interested.

guys, this is a great help as a buddy and I have had some chips in the past that were suspect, this gives me a way to check them if a question arises about their accuracy, once again thanks and a big A+ on the home work.

OK then.......MODS can we get this posted in the archives?

TC

When I pulled apart an MSD RPM Chip switch, with the variable settings and the potentiometer, the resistors I found were 1 % tolerance 1/4 watt sized resistors, red in overall color. FWIW...

This is new to me, definitely great information and I'll probably print this out. Thanks!

great info. i was going to do this a long time ago. glad someone found the time.

You guys are making things a lot more complex than they really are. I believe the RPM is the resistor value + 1000. With the 10% tolerance on the resistors, you're there. If you're not afraid of Fords, read this: Make your own