[Trevor]

Tony,

I will be accused of boasting but what the hell. I can advise you on the basis of having knowledge of the subject. Many years ago my Company, Relays NZ Pty Ltd was commissioned by Repco Ltd, to design and supply the control gear for a wheel dynamometer they were intending to produce locally.

From your comments I can see that you know exactly what you are about due to your reference to a strain gauge , torque and RPM. You are not building a dyno on a commercial basis and do not requite any form of direct read out, as is required to impress paying customers, and as was required by Repco.

You only have to register engine speed in RPM, and torque in Kilograms Meter, or Pounds Foot as is held/resisted by the retarder/brake. You can draw up a simple graph from which you can then directly read off horse power. This is in point of fact the correct way to achieve properly reliable results.

Absolute simplicity will provide maximum accuracy, and in this regard a lever operating a simple mechanical spring balance is preferable to a strain gauge. You can directly measure the lever and easily check the accuracy of the spring balance, only the calibration of the tachometer will be beyond your control. Therefore you will be able to be very confident with your results.

Direct manual control of the load applied by the retarder (brake), will enable you to record engine performance at any throttle opening. In respect of acceleration, if required this can be established against set values of torque, using a stop watch.