My mistake. I thought DynoJets used engine RPM.

I specifically remember a friend with a diesel VW on the dyno going through all kinds of hoops with a timing light and such to get an RPM pulse for his dyno pulls. This was on a DynoJet ... perhaps an older model?

 

Has to of been an older model, when I got dyno'd there wasnt a timing light hooked up

 

Timing light was only because he had a diesel ... no spark to reference for RPM.

 

Thats called an optical pickup.. A diesel has to use optical which gets the pickup off reflective tape you put on the crank pulley or on some cars the cam gears..

 

What does the optical pickup do? Get an RPM reference?

IIRC, he did this so he could get a HP reading and not just a TQ reading on the dyno. So, I assumed that the DynoJet needed that RPM signal from the vehicle for the HP formula. If that specific dyno measured RPM from the rollers, he had no reason for the optical pickup.

See my confusion? It was definately a DynoJet ... but this was back in '02 I think. It was also a 2WD and not a 4WD ...

 

Dynojets can now extrapolate torque based on speed when gearing is known. The dynojet248 that we used for a recent dyno day could belt out numbers based on either. RPM pickups obviously are preferred but not needed.

 

Optical pickup takes the RPM from a source such as the crank pulley. you put reflective tape on the crank pulley and the optical pickup can read every time the crank makes a rotation.. Its as accurate as it will ever get.. This for cars that have trouble getting rpm off the plug wires or diesel vehicles with no plug wires for example..

a dynojet dyno does not require any type of rpm to calculate HP.. its calculated based on fast you can spin the rollers in X amount of time..