crank triggers?

[ericjon262]

is there any particular reason other then packaging why crank triggers are sized the way they are?

example:

two crank triggers, one 80mm diameter, one 140mm diameter. the notches on both wheels are the same size in degrees

I could see where going smaller might cause problems, with the sensor not being able to pick up the gaps, but is there any reason a larger trigger would be a problem? seems to me like a larger sensor would be desirable, as the larger gaps would be easier for the sensor to pick up.

[fieroguru]

Packaging.

While the larger wheel has wider slots, the surface speed of the edge is also faster. Since the notches are the same duration in degrees, the time it takes the notch to pass the sensor remains the same for a given RPM.

[Shaun41178(2)]

Yes packaging, however a larger wheel will be more accurate

[ericjon262]

that seems to be the consensus on most of the forums where I've asked about it, and that's what I was thinking, I just wanted to make sure I wasn't missing something, thanks.

[The Dark Side of Will]

Larger wheel is more accurate... that's why a good many OE systems put the triggering notches on the flywheel or flexplate.

However, larger diameter means greater MOI. The MOI of a basic Chevy flexplate is approximately the same as that of the entire crankshaft, due to the dependence of MOI on the square of radius.

[ericjon262]

Larger wheel is more accurate... that's why a good many OE systems put the triggering notches on the flywheel or flexplate.

However, larger diameter means greater MOI. The MOI of a basic Chevy flexplate is approximately the same as that of the entire crankshaft, due to the dependence of MOI on the square of radius.

that makes sense, it wouldn't be too big though, def not flexplate big, probably only about 7", but I haven't measured yet.