Dallas
Ford Mustang: 5.0L and Cobra Technical Forum


Even geeks make errors...
Posted By: FiveOh (38.220.252.2) Posted on Date: June 24, 1999 at 08:50:06
In Reply to: Here's a geeks take on it... FiveOh on June 24, 1999 at 08:46:12:
Message Text:  
Click Where did you get your 3000RPM resistance from? I ignored it and did a little math on it and found that the formula to calculate the necessary R for any RPM becomes:
(RPM-1355.33)0.985=R

This give the following RPM's for your pills

5203,5396,5589 & 5802

If you assume the pills are slightly off and then assume the 200ohm/200RPM, your formula becomes:

(RPM-1410)1.0=R

Your number will be right on. If this is true, your RPM pill errors are as follows:

5000=5000
5200=5200
5400=5390
5600=5580
5800=5790

I think I would average the error out and use the formula:

(RPM-1418)1.0=R

To give you:

5000=5008
5200=5208
5400=5398
5600=5588
5800=5798

In electrical terms, put 1418ohm resistance in series with your pot or the switch idea with each one having 200ohms.

Good Luck,
FiveOh

: Where did you get your 3000RPM resistance from? I ignored it and did a little math on it and found that the formula to calculate the necessary R for any RPM becomes:

: (RPM-1355.33)0.985=R

: This give the following R's

: 5203,5396,5589 & 5802

: If you assume the pills are slightly off and then assume the 200ohm/200RPM, your formula becomes:

: (RPM-1410)1.0=R

: Your number will be right on. If this is true, your RPM pill errors are as follows:

: 5000=5000
: 5200=5200
: 5400=5390
: 5600=5580
: 5800=5790

: I think I would average the error out and use the formula:

: (RPM-1418)1.0=R

: To give you:

: 5000=5008
: 5200=5208
: 5400=5398
: 5600=5588
: 5800=5798

: In electrical terms, put 1418ohm resistance in series with your pot or the switch idea with each one having 200ohms.

: Good Luck,
: FiveOh
: : Well, the Autometer people are apparently smarter (or are they?) than the MSD people. Read farther down my board at my idea of using either a potentiometer or better yeeet, a series of resistors in series with on off switches to allow me to easily select any rpm value without buying a whole bunch of little pills. MSD uses a simple formula (add 1000 to resistance value to get rpm) such that 4000 Ohms is 5000 rpm, 2700 Ohms is 3700 rpm, etc.

: : I tested my Autometer pills and this is what I found:
: : RPM......kilo-Ohms (difference from rpm prior)
: : 3000.....1.88
: : 5000.....3.59
: : 5200.....3.79 (200 Ohms)
: : 5400.....3.98 (190 Ohms)
: : 5600.....4.17 (190 Ohms)
: : 5800.....4.38 (210 Ohms)

: : So, it appears there is approximately 200 Ohms/200 rpm OR 1 Ohm per 1 rpm, BUT, the scale doesn't fit for teh 3000-5000 spacing. That ends up being more like 170 Ohms per 200 rpm.

: : Do you think these are just production tolerance variances and that I may even be MORE accurate by starting at 3600 Ohms for 5000 rpm and go up 100 ohms for every 100 rpm?

: : Can someone else test their rpm pills and see what they end up as? Another rpm range would be great as well.
: : Thanks all - this idea wil be neat if I can get it all figured out..
: : jay
: : 95gt

:


Read Replies


Post A Reply
Name:
E-Mail:
Subject:

Comments: