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High flow impeller for 05 yz85

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I am building a hillclimb bike. The bike is, well started as, a 2005 yz85. Doin a big bore and stroker crank. The biggest problem we have seen and heard is the cooling. I can find oversized radiators all day long but after long amounts of frustrated searching i cannot find a high flow impeller or kit for this bike. Does anyone know of or have any suggestions for the pump?

Thanks

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Impeller won't do anything for over heating. Water transfers so much heat per time. The amount of cooling depends on the time in the radiator, and the amount of heat in the water depends on the time in the motor. Less time in both, high flow impeller, puts you at the same spot as stock. Larger radiators are the only thing that will make a difference. More water to hold heat, and more time in the radiator to cool.

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Never thought of it that way. But makes perfect sense. Thanks for the info.

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Never thought of it that way. But makes perfect sense. Thanks for the info.

 

It makes perfect sense but it is completely wrong.  The faster you can pump water through the radiator the more efficient the radiator will be.  Remember, you need temperature differential to drive heat transfer so if the radiator is not hot, it is not transferring heat.

 

Adding a fan would certainly fix the problem.  In my tug boat world when we size the keel coolers they are generally sized for a 2-3 knot current under the boat (that's not very fast) but our boats have overheating problems when pushing full power at a stand still.  There is literally a 50% reduction in capacity between 2-3 knots and 0.  Anything you can do to pick up airflow over the radiator will make a HUGE difference in capacity.

Edited by 1987CR250R

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Water transfers so much heat per time. The amount of cooling depends on the time in the radiator, and the amount of heat in the water depends on the time in the motor. Less time in both, high flow impeller, puts you at the same spot as stock.

 

 

This appears to ignore convective heat transfer.  If it were entirely time dependent, it might actually be better to remove the impeller and go with nothing but thermal buoyancy to circulate the coolant.  "Blowing" water through the radiator faster works better for the same reason that blowing air over it faster works better.

 

Apart from the effects of convection, heat transfer depends in part on the temperature difference between the hotter and colder components.  Transfer is fastest when the temperature delta is greatest, and the rate of transfer drops off as the two become closer to the same temp.  There is, therefore, a point beyond which it will be more productive to move the cooler coolant out of the radiator and replace it with hotter coolant from the engine to keep the transfer rate higher. 

 

Nevertheless, on a hill climber, the problem is often heavy engine loads and low forward speed, resulting in a lack of air flow over the radiator.  The solution then would be a battery powered fan.

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This appears to ignore convective heat transfer.  If it were entirely time dependent, it might actually be better to remove the impeller and go with nothing but thermal buoyancy to circulate the coolant.  "Blowing" water through the radiator faster works better for the same reason that blowing air over it faster works better.

 

Apart from the effects of convection, heat transfer depends in part on the temperature difference between the hotter and colder components.  Transfer is fastest when the temperature delta is greatest, and the rate of transfer drops of as the two become closer tot he same temp.  There is, therefore, a point beyond which it will be more productive to move the cooler coolant out of the radiator and replace it with hotter coolant from the engine to keep the transfer rate higher. 

 

Nevertheless, on a hill climber, the problem is often heavy engine loads and low forward speed, resulting in a lack of air flow over the radiator.  The solution then would be a battery powered fan.

Okay, I got half of it.

 

I'm not taking heat transfer until next spring, but I follow what you're saying. 

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The fan in anmoption we are toying with right now. Small bike to fit a lot on. Space is another issue we are having with this build also. Thanks for the explained info. Taught me enough to give me a direction for the cooling problems.

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you could reduce the clearance of the impeller to the housing if its excessive. i took the clearance from 0.08 to 0.03" with a bridgeport. don't know if it made much difference.

Edited by englertracing

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