Water pump pulley

[Jeep4xb4u]

Ok so I have pondered this idea for some time now. I don’t know if I’m the only one here, but I feel that the 4.0l water pump is not very efficient @ lower RPMs. Atleast all the ones ive installed on my renix engines. What I’ve noticed is that even with my converted cooling system, a three core radiator, a high flow thermostat housing and two spal fans, the temperature becomes very unstable at idle RPMs. When my engine is above 1000 RPMs the temp gauge floats right between 205*-220* even on a hot day. This requires me to feather the gas and brake to keep the RPMs up on occasions. Now while I’m flying down the road or have it in park and my engine is sitting @ about 1500+ the thing will sit comfortably @ about 180-200*.

To get on with my idea…

I've considered finding a smaller diameter pulley to increase the shaft RPMs of the water pump.

Some basic math:
Ratio = Crankshaft Pulley Diameter/ Water Pump Pulley Diameter
Rotor RPM = Pulley Ratio x Engine Speed

So If you take a main balancer pulley diameter of 6.5" +/- that is rotating @ 700 RPMs attached to a secondary pulley that is 5.4" +/- in diameter. The water pump shaft will be rotating @ 842 rpms. I would like to see a 200-300 +/- rpm increase @ the water pump, approximately 1100-1200.

Reverse:
Desired Rotor RPM / Engine Speed = Pulley Ratio
Crankshaft Pulley Diameter / Pulley Ratio = Water Pump Pulley Diameter

So, after throwing some numbers around I think hitting the 1200 mark is out of the question (maybe just as much as doing this period). That would require a pulley that would be 3.8" in diameter and without checking, I’m not sure you could fit something that small without modifying the pump heavily. So now I’m shooting for 1100. That would be a 260 rpm increase over stock, and would require a 4.1" pulley. This would put me closer to the range that I see the temperature start to steady out. It would be as if my engine was idling @ 960 versus the 700.

I'm sure the High flow pump that is sitting on the stroker will help out in the future but I would really like to stabilize the temps at lower rpms and lessen the time that my fans are on.

Question:
1. Has anyone done something along these lines
3. I'm going to assume that a 200-300 rpm increase is nothing to worry about on a stock redline engine. Would this be something you guys would be concerned with?
4. Does anyone have any idea of a pulley that might be a good start? Something roughly 4.0 - 4.3" in diameter, not grooved, and has a nice flat face to work with.

[Jeep4xb4u]

No ideas? I guese im on my own here.

[Muad'Dib]

Found this on NAXJA:

http://www.naxja.org/forum/showthread.php?t=991904

Would make since that a slightly smaller pulley would do what your asking. Even just a slight bit smaller would help a lot because of how low the RPMS get on these Straight Sixes.

[Jeep4xb4u]

Interesting Muad. Apparently I’m not completely alone.

I might be jumping to conclusions, but I’m sure the extra water flow would not hurt. I might be heading to the JY this next weekend for some other parts. I’ll be sure to keep an eye out for something that might work. Unfortunately I think the hardest part about it is that there are no ribs on the pulley.

[John]

You might be having a airflow problem as the root issue, Many of the 3 row radiators are more air restrictive than a 2 row, you mention 2 spal fans, but I am curious about your shrouding and how the spal setup is done, Picking up the water pump rpm might be covering the problem, not many of us are overheating, with much less cooling modifications. Trapped air, faulty new thermostat, bent or loose fins on the radiator can also duplicate your description.
John