much less water use and you could run the engine in for much longer - say even half an hour if you wanted, because most dynos are really intended/designed for short-preiod use.
I worked at Frontier in the mid 90's on a UAV helicopter project. Specifically a 6cyl 6L diesel. I was designing the internals. At the time the helicopter was being flown with a highly modified 6cyl Subaru. I remember the engine builder they had not being impressive. He was tasked with making getting more power from the Subaru, and keep it reliable. The engine failed twice in flight, causing extensive and expensive damage to the helicopter.
So the chief engineer (Ex Lotus chief engineer) went to the UK to look at ready to install Subaru Rally motors. He went to a facility that was running up a new subaru engine. As he was talking to the engineer, the engineer ran the engine upto full power, and said (as one does in England) "let's get a cuppa tea" So they went away, and talked details cost (35kukp at the time) delivery etc, for maybe 30 minutes. Then went back to the dyno room where the engine was still running flat out, and continued to do so for another 30 minutes before they shut it down. That setup would have been ideal. Powers to be didn't buy the rally subaru, and went on to have at least one more failure.
I'd like to have seen how they dissapated what was maybe 200kw of heat for 60 minutes.
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My Dad used to make load banks for Petter diesel, when they were selling gen-sets. These were large steel boxes full of heater elements. They would test the generator by attaching the generator to these load banks. Each bank could handle 50Kw, and the bigger the generator the more load banks they would put in series. I remember the load banks as at the time i was 10-11 years old and able to get my hands inside these assemblies to tighten the fasteners, my dads hands being too large. After a day of doing that I might get an ice-cream.