Gate valve, and by using a gate valve along with a hydraulic pressure gauge I could crank the valve knob down with the engine running at wide open throttle and I could watch the gauge and adjust the gate valve to get the highest PSI reading and of course that was the peak power level.
Yes you can use a torque meter. I used a Clayton water brake engine dyno for years to break in all the gas and diesel engines of all types I rebuilt at my job I worked at for 38 years. That dyno used a electronic transducer mounted on the water brake turbine housing that sensed the torque that was induced and fed it to the main gauge panel. I had different gauges to monitor exhaust temps (pyrometers) and manometers which I use to monitor crankcase pressure which you could actually tell when the piston rings began to seat. I also had a chassis dyno that I used too. As far as a filter on the return line you will need to select a filter base that has larger ports than the line that you are using on the return line and select a filter that has more GPM rating above the pump that you are using by about 50% with at least a 10 micron rating. Another factor of course is the viscosity of the oil you are using in your tank and the temperature of the oil.
Very cool little project. I was just about to start building a similar unit when this dropped into my lap for the right price. I also managed to get a full software setup and load cell from another guys aborted project. Need to build a new frame to suit my setup, a bit higher budget than your project but still cheap fun.
