292 water pump pulley ratio v/s coolant flow rate ?

[tarussell]

I’ve been think’n and need some input from some fellow gear head brethren…

I’ve gathered several parts for a 292 engine and am wondering about the water pump to crank pulley ratios on certain applications.

Most have a overdriven ( smaller than the crank pulley ) pump pulley ratio but every application that I have ( four different K-30’s ) that have come from K-30’s with 4.56 gears and have a larger water pump pulleys that is equal to the crank pulley making it a 1:1 ratio ( both being 7-3/8” diameter ) resulting in a slightly slower coolant flow rate.
I am wondering if this is due to the motor being able to be rev’d fairly high at sustained highway speeds and maybe the coolant flow would benefit from a slower rate and less pressure at such engine speeds caused by the low gearing - any thoughts or wisdom y’all could share with a knuckle-dragger ?

This also led me to another thought - up until 1974 these truck only 292’s came with a very larger coolant bypass hose ( 1-3/4” v/s 5/8” ) off of the water pump ( see pics ) and all of these seem to come with a smaller diameter W/P pulley that causes a higher flow rate - but after ‘74 they came with a smaller bypass hose and some came with the larger W/P pulleys slowing down the coolant flow.
Also, the C40,50 & 60 series still came with the larger bypass hose diameter and larger 7-3/8” W/P pulley and I assume this aids better in cooling while an engine is being worked hard and rev’d high.

Is my think’n in the right ballpark about the correlation between the ratios pulleys and coolant flow rates and their effects on extra cooling ?
I’ve got both setups that I can use but I would like to confirm that one setup is better for certain applications before I commit to using them.

Thanks, Tom

 

[imiceman44]

I don't have knowledge on the subject but I have common sense and scientific knowledge about thermodynamics and I would say you are on the right track with your analysis

 

[tarussell]

I’m with ya on the basics of common sense knowledge achieved by graduating from a lifetime of attending the school of hard knocks.

The overdriven pulley ratios obviously turns faster and creates more flow pressures and that’s a good thing until cavitation starts happening or too much pressure is created and at that point things need to slow down so the water can actually absorb and reject the heat in the water being moved throughout the system.

The higher volume and pressure is why I am thinking the extra large bypass hose/port is needed and the 1:1 pulley ratio seems to be used only on very low geared applications to slow the flow and lessen the pressure in the system - I assume all of this is correct but I’m curious to see what others think or know on this topic.
Any input on any type of motor is appreciated - what do y’all think ?

 

[imiceman44]

I’m with ya on the basics of common sense knowledge achieved by graduating from a lifetime of attending the school of hard knocks.

The overdriven pulley ratios obviously turns faster and creates more flow pressures and that’s a good thing until cavitation starts happening or too much pressure is created and at that point things need to slow down so the water can actually absorb and reject the heat in the water being moved throughout the system.

The higher volume and pressure is why I am thinking the extra large bypass hose/port is needed and the 1:1 pulley ratio seems to be used only on very low geared applications to slow the flow and lessen the pressure in the system - I assume all of this is correct but I’m curious to see what others think or know on this topic.
Any input on any type of motor is appreciated - what do y’all think ?

I think the engine type also mattered, the straight 6 had a lower rpm range so probably had different ratio pulleys than a v8

 

[tarussell]

I think the engine type also mattered, the straight 6 had a lower rpm range so probably had different ratio pulleys than a v8

I don’t think the basic power curve of the engine mattered on the pulley ratios per engine type as the operating RPM range was very similar on smog era truck engines from in-lines, SBC’s and peanut-port BBC’s - they were all outta breath by 4K.
I also did the ratio math on several types of engines ( mostly GM, Ford Windsor, 240/300, 385 series and FE, as well as 440 medium truck stuff ) and the pulley ratios were all very similar from around 1.2 to 1:1 and the 1:1 ratios mostly seem to be on the work truck engine regardless of engine type.

It’s interesting to see how much testing and engineering went into external component details by the OEM’s for different applications. They take so many short cuts and so often cater to the bean counters but some things make enough of a difference to make it into production.

 

[Bent77]

I’d think they are different ratios because the length of the block

 

[tarussell]

I’d think they are different ratios because the length of the block

That does sound plausible if it were used on all 292’s but some came with a smaller diameter W/P pulley while others were larger at a 1:1 ratio so it seems to be by application and not a year model change type of thing?
The taller deck height of the 292’s ( 1-3/4” or 1-7/8” can’t recall at the moment ) might very well be the reason for the W/P bypass port as the other inline engines of that era don’t come with it at all - the impeller on the 292 W/P is larger as well over the smaller engines.