who is running pusher fans?
07-12-2014 | 12:55 PM
#121
TECH Addict
Joined: Dec 2010
Posts: 2,610
Likes: 4
From: Maricopa, AZ
I'm not sure if everyone understands the freed horsepower from the EWP.
1. The mechanical pump is driven of the motor and increases horsepower loss as RPM increases (meaning low drag at idle and high drag at redline where its 11hp).
2. The power for the electric pump can come from the alternator or the battery. It's power requirement is fixed and does NOT vary with engine RPM.
That means the pump is always cooling the same regardless of RPM. On the street that means you are probably flowing MORE water at lower rpm (cruising) and less when at the redline. Unless you are building a road race car that will be at peak rpm for a very long time, the EWP is probably better. It will free some mechanical horsepower but will also add more drain on the electrical system. The impeller could also be more efficient.
Definitely when accelerating you are no longer having to move the mechanical gear, drive and more importantly, accelerating WATER as the RPM climbs. Water is heavy. Moving it at a constant flow rate as the EWP does should also be more efficient since you are not accelerating it.
1. The mechanical pump is driven of the motor and increases horsepower loss as RPM increases (meaning low drag at idle and high drag at redline where its 11hp).
2. The power for the electric pump can come from the alternator or the battery. It's power requirement is fixed and does NOT vary with engine RPM.
That means the pump is always cooling the same regardless of RPM. On the street that means you are probably flowing MORE water at lower rpm (cruising) and less when at the redline. Unless you are building a road race car that will be at peak rpm for a very long time, the EWP is probably better. It will free some mechanical horsepower but will also add more drain on the electrical system. The impeller could also be more efficient.
Definitely when accelerating you are no longer having to move the mechanical gear, drive and more importantly, accelerating WATER as the RPM climbs. Water is heavy. Moving it at a constant flow rate as the EWP does should also be more efficient since you are not accelerating it.
A mechanical water pump holding enough rpm to pump the equivalent of the electric pump in gpms will have LESS power loss than the electric one, in every single scenario, every single time. Put a car on the dyno, and rev it to 2000 rpms and measure the power. Then do it again with the electric pump and you will not notice any discernible difference. Like you stated it's accelerating the water, which is heavy. At steady state it is not.
AFTER the engine is warmed up the electric water pump is extremely beneficial, because of it's higher steady flow rates at lower RPM's in most situations. And it's benefits are limited to a certain load and power range.
The maximum cooling capacity, in BTU's, is directly proportional to the flow rate of the coolant within the system. It is also directly proportional to the air flow through the heat exchanger, and the temperature difference of the air and coolant, and the area of the heat exchanger. Change anyone of these variables and you change the effective cooling capacity of the system.
If you have a HD Meziere water pump that moves 55GPM free flow (which WILL drop when installed in a closed loop system) and nothing else in the cooling system changes the MAX cooling capacity of the system will be reduced. So no hot passes in Phoenix in August at noon. But alternatively it's minimum cooling capacity is also it's max, so it'll cool the car better in stop and go traffic especially with the AC on.
For most daily driving an F-body doesn't need much more than 20 horsepower average and the electric water pumps exceed that in cooling capacity when installed into our otherwise stock cooling system. But they are limited to roughly 80 horsepower average over time (see my post from earlier in this thread for this calculation, this is heavily dependent on ambient temperature and humidity).
So making 400hp for 13 seconds then stopping and idling for 5 minutes making 14 horsepower gives the car an average horsepower of 30 hosrepower for that 5 minute 13 second span of time. Roughly, for every flywheel horsepower you have that equivalent in thermal power lost through the radiator. This means the electric water pump will not handle the cooling needs of the engine for 13 seconds, but will easily handle it for the 5 minute cool down. This calculation is easy because the electric water pump is constant.
Hot passing my car put my runs at least 5 minutes apart, with an electric water pump I'd only need 65 seconds between runs to maintain an average output of just under 80 horsepower.
So it would, and does, work great for drag racing and stop and go traffic.
Like I said from the beginning though, it's not that it doesn't have it's benefits. It does. It's that it is NOT more efficient than a mechanical pump. That is an epistemic impossibility. And the power saved isn't from efficiency improvements, but from the actual removal of power from the cooling system.
I agree our cooling system doesn't NEED 6 or 11 horsepower and that most of that horsepower is used briefly to accelerate the coolant during runs, but the electric pumps on the market just are not strong enough to completely replace the mechanical pumps.
Last edited by hrcslam; 07-12-2014 at 01:05 PM.
07-12-2014 | 11:45 PM
#122
