It doesn't really relate to street engines, but a former customer of mine (back in my Opel parts selling days) dynoed one of his road racing engines, and found that the underdrive pulleys I sold back then (crank and water pump) were worth 4 hp on a 170 hp engine. Personally, I didn't design them for the power gain, but rather for the cooling advantages. The stock water pump is overdriven, it spins faster than the crankshaft speed (about 10%faster). At higher rpms, our racecars used to get hot FAST, the temp gauge would move in a linear fashion relative to engine rpms. The pulleys reduced water pump speed 34% and the alternator by 12%. Water temps dropped from 230 to a more manageable 200-205 degrees at 9000 + rpms. Pump cavitation was the culprit here, it was simply turning too fast. We also had to remove the thermostat and ran a 7/8" restrictor washer to slow down the water flow through the radiator, allowing more time for the water to be cooled.chuckspeed said:While we're on the subject - has anyone done an analysis of the parasitic losses of the water pump? I did this once about ten yars ago, and the result was a 5HP (prox) reduction in parasitic loss with a trimmed pump impeller - but I don't remember how much had to be trimmed.
Years ago I wrote an article in the OMC's newsletter (the BLITZ), and I harped a bit about parasitic losses. Driveline friction, rotating mass, etc. Simple things like the underdrive pulleys, electric fan instead of 7-blade (noisy) fan, lightened flywheel, sticking with 13" wheels and choosing a lightweight design (less inertia), synthetic lubricants in engine/tranny/rear axle/wheel bearings.....it all adds up. Sure, it may not gain you 20 hp, and it may seem redundant on a 65 hp stock engine, but there comes a time when your cash investments into the driveline start delivering diminishing returns, and you find that while the first 20 hp only cost you XX dollars, the next 20 will cost you XXXX dollars and be harder to get. At this point, the detail stuff starts to make sense, and 'frees up' some of that hidden horsepower.