Re: STUMPED!

[rdh@sli.com (Robert D. Houk)]

   O.K. folks, I have a tough one for you. My name is Ben Howell and I 
   posted a message a couple of days ago entitled "I NEED MORE!". I got 

Nitrous, man , nitrous. Dial in amount of $chrapnel you want!

   quite a few responses from it and I would like to thank everyone for them 
   (if there are more ideas out there, keep em' coming). Anyway, I working 
   with Autometer right now, to have them make me a five cylinder 
   tachometer. They told me this is a relatively simple process, but there's 
   a catch (isn't there always?). They need to know how many times the coil 
   pulses per revolution of the crankshaft. When I was talking with Matt in 
   the technical dept. he said that it is usually half the amount of 
   cylinders (i.e. an eight cylinder motor's coil would pulse four times per 
   revolution). This simple equation would say to me that a five cylinder 
   would pulse 2.5 times per revolution (duh). However, I was talking with 
   some of the more reputable shops in my area (Colorado) and someone 
   suggested that it might pulse 3 times on one revolution and 2 on the 
   next. If anyone knows FOR SURE what the answer is to this question I 

It doesn't matter. Yes, the ignition will fire on average every 144 de-
grees of crankshaft rotation, or on average 2.5 times per revolution, or
2 times on some revolutions and 3 times on other revolutions. It doesn't
matter. Ignition pulses / 2.5  yields RPM. Or crankshaft TDC sensor
pulses / 1 yields RPM. Or distributor "Hall" sensor * 2 yields RPM.

Of course if you're running some newfangled E-LEC-TRONIC high-energy
super duper ignition you're really up the proverbial waterway.  Many of
the aftermarker high-energy electronic ignitions will multiple-spark
the ignition "to ensure" good ignition. Some of the latest'n'greatest
even claim to "measure the effects of the first spark" and dynamically
(on the fly) decide cylinder and pulse by cylinder and pulse whether to
fire the spark once, twice, thrice, or ??? So much for counting spark
pulses . . .

					-RDH