4AGE Water Pump Cavitation Question

[racermr2]

At what rpm level does 4AGE water pump cavitate? If my question is not clear; then what are the causes of water pump cavitation?

[bermy]

I've heard a lot of numbers over the years... it's hard to really know honestly. For what it's worth, F/A engines used a 20/30 reduction for the waterpump compared to the 1.12:1 overdrive of the stock 5 rib pulley. I would make an educated guess that over 6000-7000rpm (waterpump speed, not crankshaft) it turns into a blender and doesn't move water like it's supposed to... maybe even lower that that.

[Sam_Q]

I have heard that it's at 8000rpm and above that the water near stops doing it's job. This makes sense as if this happened below the factory redline it could cause warranty issues at the time.

As above though they could be well out of their efficient range of use before then.

I am using an oversized model myself but managed to damage it a while ago due to my own sillyness. So I plan on making a replacement that only just clears the factory crank pulley. I also wish to make a new alternator pulley because they don't seem to like hitting higher revs either. I worked out my redline of 8600 I worked out it's near 20,000 at the alternator. When I took it apart I found burnt wires in the armature winding which I see as far from normal.

[bermy]

Yeah, stock setup really limits thing. It's really hard to get a big enough pulley in there to really matter. Best thing is dropping the size of the crank pulley down, effectively underdriving the alternator at the same time.

BTW Here's my setup



I have 2 waterpump size pulley to choose from. That one is 50% crank speed (48/24) and the other one is 57% (42/24). I figure that 50% might be a bit overkill. Setup has not been tested yet so I can't say if cooling is affected by it... will know in the future that's for sure Oh and alternator is driven at crank speed, which is marginal at idle, but in a carbed KE20 with no heater, radio, etc I hope to get away with it... only time will tell.

[Sam_Q]

Bermy while I find what you have done really interesting you may end up snapping your crank. Without a harmonic dampener you may have destructive harmonic pulses. 4age cranks seem to fail through the #1 big end journal

[bermy]

Bermy while I find what you have done really interesting you may end up snapping your crank. Without a harmonic dampener you may have destructive harmonic pulses. 4age cranks seem to fail through the #1 big end journal

Totally aware of that... although F/A engine seem to work fine without one... for as long as they're supposed to run anyway

[Sam_Q]

They have a billet cro-mo crank which from what I hear even that doesn't last long and is reground 4 times before being binned. Not having any form of darmonic dampening puts a high load on the bearings. Anyway getting side tracked.