t dub has a wasted spark but the exhaust/wasted spark occurs on a whole new revolution, so on a tachometer install (which I'm not even doing, this question is just driving me crazy) I want it to count every spark even though one of them is a "wasted" spark, right? because no matter what it's one spark per revolution---
sincerely,
--aspiring to wrench my own tw
I don't think so. Cut the revolution down into quarters:
- Intake
- Compression
- Detonation
- Exhaust
A spark happens very near the end of 2 and very near the end of 4, thus occuring within the same revolution. Only if the spark was more than 3 steps away from the next would it be in a different revolution, and thus wouldn't really be a wasted spark system for a 4 stroke engine. I could see how counting this out in your head might make you think it's part of a different revolution, but it's never been a full revolution until you're through all 4 quarters.
EDIT: A much simpler way is to realize you're not considering crankshaft RPM, but camshaft RPM. I was definitely reading the question weird. One spark per revolution, two sparks per complete cycle.
You still cut the number in half on those devices because it's a chicken or the egg thing. If you were wanting to know how often it sparks by reading a tach, you'd keep your thinking, but to install one, you want to know the rpm by reading a spark, so you have to divide to eliminate the wasted one.
