Aux Pulleys - Oversize Vs Undersize

[Jebus]

Discussion on pro's and cons of Undersize and Oversize Alternator and water pumps pulleys. And any experiences with either.

Had an understanding and have now become confused. Only factual answers from people who know what theyre talking about please

[Stealer Of Souls]

Compensating for high RPM operation or reducing mechanical drive loss?

[AceSniper]

there good for... "Compensating for high RPM"
Thats what im using a pair for

[Stealer Of Souls]

Holdens and Fords sometimes use underdrives to reduce mechanical drive losses to the waterpump. Because the Oz designed cars are designed to run in their hotter environment, so here in NZ you just don't need that much cooling capacity.

[Jdawg]

Another couple of reasons. In high revving engines, to stop water cavitation in water pumps and and Alternators from flying apart (have had 2 fail due to constant high revs circuit racing)

[Jebus]

So 10% oversize will slow down the acc's protecting them from sustained high RPM and cause less power loss on the engine?

[Stealer Of Souls]

Yes, but is 10% enough?
Depends how high you rev.
The power loss maybe inconsequential. Power loss is loosely related to rotating speed... So underdriving to compensate for high RPM use may not reduce power losses. Need to underdrive further than just compensation...

[Jdawg]

Or install electric drive kit on water pump if it is power loss you are worried about

[Alex B]

Then you loose power with more load on the alternator. The load does not just magically go away.

[Punter]

Then you loose power with more load on the alternator. The load does not just magically go away.

Yea but electric pumps are more efficent, and don't speed up with higher revs meaning less power used.

[Alex B]

Good points

[Stealer Of Souls]

Do i have to repeat myself many times over....
I have a Davies Craig EWP. There is no noticibly change with the EWP running at full voltage/current or off completely.

In fact on my 4AGE (~100kW @ flywheel, standard cooling system with no thermostat, EWP electronic controller) the pump barely operates at a constant load of 3V (I have yet to measure the current). Most of the time it is off, or cycling (3V for 2 seconds out of every 5).
And to add to that, the water pump load only increases as needed, not with engine RPM. So on AVERAGE the load is reduced all the time.
Add to all this that the EWP is a better design of water pump than a number of factory pumps and you can see how you end up with a net reduction in load under street conditions.
I would expect a net reduction even on the track.

The EWP is rated 14.5V @ 7.5A. That's 108.75W. Assume double conversion losses are 25%, that's a mechanical drive requirement of 145W. That's about the same effect as turning on my lights... Which on my engine results in a drop of 200rpm (@idle). Direct wiring my water pump to the battery does not result in a 200rpm drop in idle.

[sergei]

Why do you think that lights power feed is somehow separate from battery?
Battery is directly wired to alternator (no relays or other active or passive elements apart from 100+ Amp fuse). You will find that the light problem might be in bad grounding and coroded contacts and wires.... If you ever pulled toyota looms apart you will find there is really fat white wire which goes directly from battery to alternator (splitting along the way to inside and fuse box)..

[Stealer Of Souls]

Why do you think that lights power feed is somehow separate from battery?
Battery is directly wired to alternator (no relays or other active or passive elements apart from 100+ Amp fuse). You will find that the light problem might be in bad grounding and coroded contacts and wires.... If you ever pulled toyota looms apart you will find there is really fat white wire which goes directly from battery to alternator (splitting along the way to inside and fuse box)..

??????????????
I'm confused...

I have spotted a hole in my logic though...

The point was that the load effect of the EWP at full speed on the alternator was minimal.

[Jdawg]

And you will have lessened the chances of throwing a belt off, esp with large changes in rpms