View Full Version : Anyone Considered Going An Electric Water Pump

04-04-2009, 11:50 AM
Has anyone considered or gone with removing the water pump and changing to electric? Do you think we may have anything to gain in this?
I know it sounds small but thinking the bike has standard about 15nm of torque which is absolutely sweet fa. I am thinking the removal of the oil pump and water pump together maybe noticed. Not at higher rpm but at launch?

04-04-2009, 07:21 PM
I work as an engineer for a pump company...most of the pumps weigh as much as 10 or 20 RS125's put together, other pumps weigh as much as several cars put together. But the concepts are all very similar.

A small amount of torque gained at high RPM equals a very significant gain in HP. Torque is 1ftlb to 1HP at 5250RPM. So, at 10,500RPM it's 1ftlb makes 2HP so torque gains get magnified at high RPM not low.

Pumps tend to be rated in Hp not torque. The losses (efficiency) of a pump vary with RPM. You would need to make an "efficiency map" of the RPM band to know how much loss there is. This could certainly be done with a before and after map.

There certainly are other advantages to running an electric water pump. You can vary the voltage relative to cooling demand to have optimal cooling in all situations. There is most certainly an "optimal water flow" to get maximum heat extraction from the cylinder head. There is also probably an "optimal water flow" to extract heat from the radiator. Depending on how well Aprilia/Rotax did their engineering homework they may or may not be the same flow number... I would bet at max RPM the motor flows more than that number. This scenario would also allow you to eliminate the thermostat. Coolant flow (Voltage) would be indexed off of cylinder head coolant temp for maximum efficiency.

My only warning would be that the integrated mechanical water pump is a very elegant solution that rarely fails, weights almost nothing, and is already installed.

In terms of application, you would have to find out how much flow is generated by the stock water pump. A small flow meter could be put inline and flow could be measured at multiple RPM points to find the out put of the system. I recommend removing the thermostat to get a proper "head" vs flow reading.

You need to find a very durable 12v dc pump/motor combo that is properly sized. I'm pretty sure the flow required by a 125cc motor is quite small in terms of industrial applications. You're probably looking more at laboratory equipment at that flow rate. The other application would be to look at some automotive equipment. Cars like the Toyota Prius do not use 1 large water pump, they use multiple smaller electric ones to heat and cool multiple systems in the car. One of these may be the right size.

The second thing you will need is a voltage controler that can reference the coolant temp and deliver a proper voltage to the pump that is durable as the pump you choose. You need to be careful home made or very low volume electronics usually aren't very durable, especially in the automotive/motorcycle environment (hot&wet).

I've used this setup on race cars but it is way to big a package for the RS125

04-04-2009, 08:17 PM
Much, much appreciated. That is the sort of info we need to hear. Will check that site on and the toyota. I was thinking something like an electonic water pump and controller I had on my car, can't remeber what brand it was. had an inline pump with a controller boox that you could adjust what temp and volume. I would expect that most pumps would be oversized for the application though sure something is out their. Not looking at the pump expected it would be a fixed rate and then expected the greatest/ most significant load to have been on initial spin up.

04-04-2009, 08:18 PM
I will try Aprilia Aust and see if they have and if so will give me any specs on the pump, worth a try.