[Diy_efi] Crank trigger resolution

[Dave Dahlgren]

If the maximum timing is 40 BTDC and you have a signal at a few micro seconds
before that doesn't that make all the other teeth just intermediate results that
has no real bearing on when you are going to fire the spark. What good is
updating the crank position every 6 degrees in places of no particular interest
if all you need to do is control the ignition timing.

 How are you going to find 'crank twist' with a wheel mounted on the front of
the crank like electromotive with 6 teeth or 600 what would you compare it to?
If you have one at each end I could see it but not with 1 wheel.

Dave Dahlgren

Rod Hiorns wrote:
> 
> Hi guys,
> 
> How does crank trigger wheel resolution map into spark (or fuel)
> timing resolution? Numerous OEMs use 4-pulse cam-driven sensors
> but aftermarket guys like Electromotive push 60 teeth offerings.
> 
> I guess I'll know the transient timing better with more teeth,
> and can allow for crank twist at high power, but is there more
> to it than this? I've seen Mazda publish only minor HP improve-
> ments by swapping to crank trigger (at low resolution).
> 
> I'm thinking of changing a cam angle sensor for a crank trigger
> to get rid of the belt "slop", but I'm wondering how much this
> will solve. Timing jitter is obvious at the moment ... if that's
> just belt slop I'll modify the cam signal by latching it with a
> crank signal, and then advance the cam sensor so it's far enough
> ahead of the crank "edge" that the jitter doesn't come into play.
> 
> If I need to do more, what else should I be doing? Any advice is
> much appreciated.
> Cheers
> Rod
> 
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