RPM for dyno runs?

[TedV]

All the local dyno's use an inductive pickup, similar to a gasser timing light pickup, to get the RPM reading for HP, torque vs RPM.

anyone have a trick for producing this?  where to purchase? components to fabricate?  stick a timing light on my current tach wire and see if I'm really lucky???

[TedV]

Not finding anyone local I can borrow the adapter from, and at over $200 for one, there has to be a cheaper alternative.

use my tach pulse to trigger a gasser ignition module to fire a coil with a plug wire ?  All parts I have laying around the garage.

Rube Goldberg is my hero.    :lol:  :lol:

[Vincent Waldon]

Sadly there's no easy answer here.

The inductive pickup on the dyno is expecting one pulse per every two revolutions... a 50 kV pulse.

Anything hooked to the W terminal on the tach is going to be 8 or 10 times too fast... if you can get the square wave from the alt looking enough like the signal from a hall-effect transducer to fire an ignition module.

You could do the math and re-calibrate... but I'm not sure if the average dyno would handle RPM readings of 40-50K ??  Dunno if your ignition module would fire that fast, either ??

I think you'd get there quicker using a super magnet glued to the crank pulley... read it with a hall-effect stolen from a distributor (which your ignition module is expecting to see anyway)  and now you're only out by a factor of two... 10K RPM *should* be within range of the average dyno ?

In fact, tell the dyno it's an 8-cylinder and you're golden from a calibration perspective... I think ??