I guess I did not explain more of why I am asking this.
What Adam mentioned is why I am asking this. I am helping a friend find a way to connect an input to a LM2 to datalog the driveshaft RPM for calculating convertor effectiveness. He is a Buick guy, but a big block person.
I have been helping him get ready to install a data logging system in his car. He was talking to a speed shop that he deals with about componants he needs to get. They said that he needs to mount the pick up to the differential, and he is running a GM 12 bolt which has very little to no room to fasten to at the input snout.
I am thinking that, as mentioned, up toward the tranny output would be best due to movement is less than by the differential. But we do not know any particular device to order. I remember the old cruise control systems also, and know there has to be some easy setup. I am hoping someone can say.... Blah, Blah, Blah... Summit has these for $??? amount. They will provide a signal like a tachometer does.
Innovate sells a serial expander that allows an additional RPM input, we just need to device to give the signal.
Thanks again for the inputs. It is very much appreciated.
Mike