rx7locost wrote: The dyno he has is a water brake dyno. It has an impeller with vanes that is directly coupled to the crankshaft via a modified driveshaft. The dyno housing also has vanes. The water/antifreeze acts as a viscous coupling between the two, the amount of water in the dyno cell (brake) controls the amount of torque loaded. The brake is pivoted about its center and has an arm which is attached to a hydraulic cylinder mounted to the frame. From the cylinder, a hydraulic line goes to the pressure gauge on the console. It is calibrated such that you multiply that reading x RPM /1000 to get HP. There is a tachometer on the driven shaft to monitor engine RPM. Think of it as a bucket with a hole in the bottom. The bucket drains at some consistent rate of flow. Then take a hose and try to fill the bucket. The more water you let in, the more water is in the bucket (the water brake). Slow down the flow and the water in the bucket lowers. This is how the dyno applies more or less drag on the engine.
Since he uses the dyno mainly for his Formula Vee, the engine stand is simply a stripped out transaxle housing with an input shaft attached to a short driveshaft connected to the brake. Mount the engine under test to the housing, attach all the fuel, throttle, cooling fans and various engine sensors and away you go. That takes about 2 hours setup time.
Rather than using a waste water system, He uses a closed loop system. A 55 gallon drum is filled with water/antifreeze mix. Then, there is an electric pump to pump the water from the drum into the brake, controlled via a flow control valve on the console. More flow, the more the brake fills and the more torque applied. The drain water from the brake falls into a container that has a sump pump which pumps the water back into the 55 gallon drum. The engine’s energy has to go somewhere. In this setup, it heats up the water. There is a temp gauge to monitor the drain water. If it gets above 140deg, it is too high and may boil. If it does boil, the engine’s RPM takes off since the test is done at full throttle. Not a good thing to have happen especially if you are taking measurements at, say, 6,000 RPM.
The control console has a RPM gauge, torque meter, water flow indicator, drain water temperature gauge, oil pressure gauge, Cylinder head temperature gauge, and a few other gauges which we did not use. It has a throttle lever and the flow control lever for the water brake. Keeping an eye on all of the gauges while trying to hold full throttle and control the load of the brake, read and write down readings at once is a bit daunting.
To perform a dyno run, it is simply warm up the engine, and then open the throttle while applying more and more torque till you have the throttle fully open and the engine loaded to 3000RPM. Try to hold that RPM using the flow control. When you have a stable RPM, take a reading and record. Then back off the flow and try to hold 4000 RPM…. Repeat as required; all the time checking the drain water temp and the oil pressure and head temperature and; and; and so you don’t accidentally blow the new engine.
As for the neighbors complaining, well, he is about 100 ft back from the highway. Next to him is a funeral home. Nobody was being waked at the time. And across the highway is a nursing home. In over 30 years there he has never had any complaints. I guess it wouldn’t be welcomed in a “normal” subdivision.
It was certainly a good education for me.
How long does he usually get before the water heats up? I've been looking into making an engine dyno with a stuska brake or a large torque convertor, but I've got to stay with a closed system as well, and my math was pointing towards gigantic tanks (500 gallons and up). Is it just because Formula Vee engines are fairly low HP, or is there a lot of downtime for water to cool while tuning?
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