REPROGRAMMING MSD RPM PILLS
Various ignition systems and accessories are often configured to do certain things at a particular RPM level. These devices may be used to set a rev limit, a stage limit, trigger a shift-light, or even activate a nitrous system. The popular systems made by MSD utilize external replaceable modules called "pills" to select that point based on a pre-determined resistance value. The following pictures detail how to disassemble and reassemble an MSD RPM pill, thus allowing that point to be modified as desired. This is especially useful if your application requires a non-standard set point or it's 10pm the night before the drags and you don't happen to have the required pill handy. Even a potentiometer works wonders in a jam!
Refer to the chart below to select the proper resistor value. For most applications it's not essential to have the exact resistor listed and you may choose to adjust the value up or down slightly to fit your needs. If you're familiar with resistors, you can easily combine them to create virtually any value you require.
RPM Ohms
100 10.8
200 10.9
300 11
400 11.1
500 11.7
600 101
700 191
800 274
900 354
1000 432
1100 506
1200 580
1300 653
1400 724
1500 795
1600 867
1700 937
1800 1010
1900 1081
2000 1152
2100 1224
2200 1297
2300 1370
2400 1444
2500 1518
2600 1592
2700 1668
2800 1744
2900 1820
3000 1896
3100 1978
3200 2049
3300 2132
3400 2215
3500 2288
3600 2373
3700 2460
3800 2534
3900 2622
4000 2710
4100 2787
4200 2877
4300 2969
4400 3048
4500 3141
4600 3235
4700 3316
4800 3412
4900 3509
5000 3592
5100 3691
5200 3791
5300 3877
5400 3979
5500 4082
5600 4171
5700 4277
5800 4383
5900 4475
6000 4584
6100 4693
6200 4788
6300 4901
6400 5014
6500 5112
6600 5232
6700 5349
6800 5449
6900 5569
7000 5689
7100 5793
7200 5919
7300 6043
7400 6150
7500 6277
7600 6406
7700 6517
7800 6649
7900 6782
8000 6897
8100 7034
8200 7171
8300 7291
8400 7432
8500 7575
8600 7699
8700 7845
8800 7994
8900 8122
9000 8274
9100 8428
9200 8561
9300 8719
9400 8879
9500 9018
9600 9182
9700 9348
9800 9491
9900 9662
10000 9834
Notes:
All resistors are 1/4W rated. To enable the switch at all times, 0 ohms/shorting wire may be used. *Values below 500 RPM are not consistent, nor recommended and this range would typically be impractical.
Here's a graph of the resistance versus RPM:
I highly recommend using precision metal film resistors (like the quality ones used by MSD) and not the typical carbon ones found at places like Radio Shack. In a pinch they'll probably do, but the carbon based type are far more sensitive to heat/humidity and as a result their resistance can change, sometimes by a huge percentage. If you're mounting the RPM switch inside the interior of the car, it's probably not as big of a deal, but just be sure to do some of your own testing to verify proper operation under normal conditions.
Here's a typical MSD RPM Pill:
Here's one with the label removed by simply lifting an edge and peeling it back. There may also be a small amount of hot melt type glue underneath that you can easily pull out with a pair of tweezers.
There are a couple methods of removing the internal resistor. You can use a de-soldering tool (i.e. a solder sucker) and remove all the solder from the end of each hollow post, or if you don't have one of those available, you can simply heat one post at a time and gently pull the resistor lead out a little bit, then switch to the other lead, and repeat as necessary (see photo series below). If you use the latter method, you'll have to do the same in reverse to install the new resistor. The de-soldering method is much better and far quicker/easier, but either will work just fine.
Here's all the guts…there's not much to it!
Select your new resistor value, or the closest one available. Gently bend the leads at 90 degree angles, trim both to approximately 3/4", and place back into the holder. Re-solder by heating the post and flowing solder into it.
Viola! Ready for testing.
If you just need a standard value, can't locate the proper resistor, or simply don't have the required skills or equipment to do this, you can visit MSD's web site for information on obtaining plug-n-play pills by clicking here:
www.msdignition.com
NO WARRANTY IS EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
WHILE EVERY EFFORT HAS BEEN TAKEN TO ENSURE THE ACCURACY OF THE INFORMATION CONTAINED WITHIN THIS DOCUMENT, IT IS YOUR RESPONSIBILITY TO VERIFY THE USEFULLNESS AND SUITABILITY FOR YOUR PARTICULAR APPLICATION PRIOR TO USE.