- Oct 18, 2003
- Saline Michigan
Critical cases on cooling modern cars are usually protracted idle and Davis Dam/Baker Hill, all corrected to 100F with AC on Max. Davis Dam and Baker Hill are miles at 7% grade and 35 mph on a 100 F day with the AC in max. This is typically around 2000 rpm and medium throttle, the transmissioncooler and AC condensor are dumping heat on the radiator and even the radiator is usually sized based on this test condition. The pump size and spin speeds are selected to be a little bigger than needed for that. Once you have enough flow for Davis Dam and Baker Hill, the other conditions are usually well covered.Yes Bill, I will be spinning the water pump impeller at a higher equivalent speed than the engine but will not be anywhere near redline RPM on it. The tip speed will still be well below cavitation speed. I am running smaller than stock diameter coolant lines so will see more restriction. This was also because the pulley I used is an aluminum one I can source easily and shed some weight but also fit the alternator where I want. It's all a compromise isn't it?
Ross over at SDS (rv6ejguy on here) has a bunch of experience with high performance ground vehicles and auto conversions in airplanes, with thousands of his systems running. Good reading... I do not remember him ever talking about raising accessory speeds on any conversions for airplanes, and he uses small coolant tubes too.
Airplanes cannot even run at the critical point on car engines (30-35% rpm/75% torque/low air speed) that the car guys live in - a good flight propellor can not make much torque/power at 30% rpm - they need to run in the 75-90% rpm range for flight, where we have a lot of airspeed and a lot of pump rpm.
Unless I had some good data or a downtown level analysis indicating I needed the coolant pump to be spun faster than stock, I would be really reluctant to do it. Costs you horsepower better spent turning the prop and has to shorten bearing and seal life in the coolant pump too.