"Johnson, Darren" wrote:

With the issues I have been reading about the last couple of weeks with
the water pump is anyone running or considering running an electric
water pump?  I know they are primarily used to insure good flow at low
RPM's, not a condition we really worry to much about except in a long
taxi.  I know in V-6/8's I have seen claims of recovering 20-30 hp by
using electric vs. mechanical.  The only two reasons I can see not to
use them would be 1) another thing using electricity if you had an
alternator failure and 2) if you use the full controller setup it adds
about 6 pounds or so.

I should have something on the web site like: "Why you should not
use an electric water pump."

1. It takes about 1 to 3 HP to pump enough water through a Mazda
rotary engine running at 150 to 200 HP continuous to cool it.
There are no two ways about that.

2. One HP is 756 watts. It is not just a good idea. It is the law!

3. 756 watts at 14 volts is 54 amps. Power = current times voltage.

4. Show me an electric pump that will draw 54 amps.

5. There is no magic in an electric pump. It uses the same
technology that a mechanical pump uses. There have been no
significant changes in the past 100 years on how much
water that can be pumped with a given amount of HP
despite the outrageous claims of the scam artist electric pump
makers.

Paul Lamar

Paul,  could you drive the water pump with and extended shaft from a turbo charger through a gear
set?  Instead of trying to capture the excess power of the turbo through compounding.  Perhaps it
could pump the water and augment the power by saving that 3 horse power.

Tom Webber

The thing is 50% of the energy in a gallon of gas goes out the
exhaust in the form of waste heat. 30% is useful mechanical shaft energy
another 20% is waste heat in the cooling system.
So asking the exhaust to provide only 3 hp is a waste of the potential.
Turbo compound engines such as the R3350TC were recovering 12% of the 
waste energy in the exhaust 50 years ago. Surely somebody can do better 
today. If you are going to spend all that money you should go
for maximum effect.

13B Heat balance:
shaft 200 HP
cooling 133 HP
exhaust 333 HP

12% of 333 is 40 HP more.  Total engine HP goes to 240. 
No increase in cooling load or fuel burn.

Paul Lamar
 
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