Overdriven pulley how much is too much?

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Kenflo

Kenflo

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Looking at new pulleys and came across the CVF serpentine conversion. There is no info on their web site regarding ratio or pulley diameter (I plan on calling them Monday). I did read a post on here saying the crank pulley is 6.25 and water pump pulley is 5.125 making the ratio 1:22 overdriven. I do not have AC and plan on using the Mopar performance 4140063 5 blade fan with 2947 Hayden clutch along with a high volume water pump. My main concern (and may not even be a concern) is this combo could cause issues like over heating or damage to the fan/clutch?
My current set up is basically factory pulleys 318/340 spec with 0.95:1 water pump ratio. Does overdriving the water pump/fan in a non ac car cause issues? Or is it a good thing?
 
Overdrive will be better almost all the time. Won't cause a single issue. Make sure the radiator is clean and suited to the application.

I've got a flow kooler wp, 5 blade fan, shroud, Hayden clutch, champion 26" alum radiator, and stock pullies and my 10:1 408 with headers will creep from 195 to 210ish if I stay idling. It drops back to 195 as soon as I move forward at any speed or if I rev the engine. I'd bet over driving my pullies would keep the temp solid.
 
My combo is under-driven in the hopes that the V-belt will stay on the pulleys at 7200. In 20 years, so far so good.
I fixed my overheat issues decades ago by running my pistons and top gap a hair loose, and with a 7-blade all-steel fan off a mid-70's A/C equipped 318 Swinger. Same car donated it's rad. I run a thermostatic clutch, and the coolant runs 205 .And yes, to the obligatory hi-flo pump.
 
Well Gentleman, I have had the opposite effect.
The water goes thru my radiators too fast and does
not have sufficient time to cool as effectively.
 
GTX JOHN said:
Well Gentleman, I have had the opposite effect.
The water goes thru my radiators too fast and does
not have sufficient time to cool as effectively.
Click to expand...
I wish we could put that wives tale to rest. This might happen but not for the reason you say. It might be caused by turbulence in the block, preventing heat exchange. There used to be a cooling/ rad website that refuted this claim.

Here is one:

Tech Tip #3: Thermostats & Restrictors - Stewart Components

Thermostats & Restrictors We strongly recommend NEVER using a restrictor: they decrease coolant flow and ultimately inhibit cooling. For applications requiring a thermostat to keep the engine at operating temperature, we recommend using a Stewart/Robertshaw high flow thermostat. This thermostat...
www.stewartcomponents.com www.stewartcomponents.com
 
I do stand by my observations.

I do post what I have seen personally in
60 plus years in this hobby.

I do speculate on the causes of what I have
observed in person.

I do not post what I have read anywhere as I consider
that to be "here say".

I do not insult or impugn anyone who has different
opinions or experiences that differs from mine.
 
Last edited:
Restrictor Plates are more commonly used on race cars
that often have high volume electric cooling systems.
They are often on Drag Racing cars that run short periods
and often the goals are to stage at around 100 degrees or
less and complete the run around 120 degrees. I Never advoccated
them on anything but some Drag Race applications.

I have experimented with different drive pulleys (Electric Pumps)
how and observed how the speed of the coolant affects the efficiency
of the cooling process. This is for 50 years and over a career of Drag Racing
and both on and Offroad Racing, not to mention Drift and Slalom. My older
boy has been a Crew Chief on a Pro Drift Team and a Baja 1000 class winner.
Also, he manages one of the major racing experience venues on the west Coast.
Cooling is Paramount on all these venues.

I believe Mopar has engineered the pulley size to be the most effective
for the engine combination. They even had a different water pump with
different vanes for Air Conditioning cars. I am sure that minor changes
in drive speed are irrelevant but to go overboard is ill advised for cooling.one

I may or may not be correct on my posts on this site = but they are honestly
posted from my personal experience with the intent of being of utility to my
friends on this site. If I get enough feedback that they are unwelcome or
misleading = I will be out of here. I have plenty to do in our shop with a dozen race cars
in it.

This is my background/context that I speak from and I am indeed guilty
of being an Old Man.

However, I would not advise you calling me an Old Wife to my face unless
you are on a first name basis with a good dentist (You WILL need one).
 
Last edited:
Been doing some research and I was comparing some specs for the 340 engine on the factory service manuals:
1973 manual says water pump to crank ratio is:
STD 1.2:1
Max cooling no AC 1.2:1
AC 1.3:1
Max cooling AC 1.3:1
water pump impeller STD & AC 3.7" 6 blade
1972 manual says water pump to crank ratio is:
STD 0.95:1
AC 1.3:1
water pump impeller STD 4.38" 8 blade & AC 3.7" 6 blade

So with the serpentine system I should be OK I'm thinking as the factory spec shows overdriven fan/water pump ratio as well. I will still call be calling CVF to verify the ratio and pulley diameters to be sure.
 
GTX JOHN said:
Well Gentleman, I have had the opposite effect.
The water goes thru my radiators too fast and does
not have sufficient time to cool as effectively.
Click to expand...

This is thermodynamic hokum. The physics of heat transfer simply do not support this in any way, shape, or form.

Now, there are more factors than just heat transfer at play, turbulence, cavitation, heat pockets in the block, etc and those can change how some of that stuff works.

But just saying that the water is going too fast through the radiator to cool? Nope. Heat transfer occurs at the molecular level, and molecules transfer energy a heck of a lot faster than the water in your radiator flows. And while time is a factor in the amount of cooling that occurs, faster coolant speeds also means more “trips” through the radiator. So what cooling may be lost on a single pass is compensated by making more passes in a given time.

Not discounting your experience, but, your changes in cooling were 100% caused by something other than just coolant speed.

Kenflo said:
Been doing some research and I was comparing some specs for the 340 engine on the factory service manuals:
1973 manual says water pump to crank ratio is:
STD 1.2:1
Max cooling no AC 1.2:1
AC 1.3:1
Max cooling AC 1.3:1
water pump impeller STD & AC 3.7" 6 blade
1972 manual says water pump to crank ratio is:
STD 0.95:1
AC 1.3:1
water pump impeller STD 4.38" 8 blade & AC 3.7" 6 blade

So with the serpentine system I should be OK I'm thinking as the factory spec shows overdriven fan/water pump ratio as well. I will still call be calling CVF to verify the ratio and pulley diameters to be sure.
Click to expand...

Yes, the factory used a .95:1 ratio with the high volume water pump and a 1.3:1 ratio with the standard water pump.

This likely had everything to do with fan speed and moving more air than it did with the water pump, which is why the overdriven systems used a lower output water pump. You can definitely spin the water pump too fast, which can cause a loss of efficiency from turbulence or even cavitation in extreme circumstances. The same is actually true of the fan blades as well, they’re designed to spin at certain RPM’s and are most effective within a certain range. So, keep that in mind when picking your components. The factory was balancing fan speed and water pump speed for best effect in both air and water flow, and multiple components were changed on the standard cars vs the AC cars. The whole of the system is what has to be considered, just overdriving the pump/fan may not have the best results unless you have a pump and fan that work best at that higher driven speed.
 
72bluNblu said:
This is thermodynamic hokum. The physics of heat transfer simply do not support this in any way, shape, or form.

Now, there are more factors than just heat transfer at play, turbulence, cavitation, heat pockets in the block, etc and those can change how some of that stuff works.

But just saying that the water is going too fast through the radiator to cool? Nope. Heat transfer occurs at the molecular level, and molecules transfer energy a heck of a lot faster than the water in your radiator flows. And while time is a factor in the amount of cooling that occurs, faster coolant speeds also means more “trips” through the radiator. So what cooling may be lost on a single pass is compensated by making more passes in a given time.

Not discounting your experience, but, your changes in cooling were 100% caused by something other than just coolant speed.



Yes, the factory used a .95:1 ratio with the high volume water pump and a 1.3:1 ratio with the standard water pump.

This likely had everything to do with fan speed and moving more air than it did with the water pump, which is why the overdriven systems used a lower output water pump. You can definitely spin the water pump too fast, which can cause a loss of efficiency from turbulence or even cavitation in extreme circumstances. The same is actually true of the fan blades as well, they’re designed to spin at certain RPM’s and are most effective within a certain range. So, keep that in mind when picking your components. The factory was balancing fan speed and water pump speed for best effect in both air and water flow, and multiple components were changed on the standard cars vs the AC cars. The whole of the system is what has to be considered, just overdriving the pump/fan may not have the best results unless you have a pump and fan that work best at that higher driven speed.
Click to expand...
Good info indeed! Maybe I need to consider with this particular combo using a standard water pump instead of a high volume like the factory. 6 blade? The water pump I intend on using is the flow kooler which seems to have a anti cavitation type impeller.
 
Kenflo said:
Good info indeed! Maybe I need to consider with this particular combo using a standard water pump instead of a high volume like the factory. 6 blade? The water pump I intend on using is the flow kooler which seems to have a anti cavitation type impeller.
Click to expand...

Realistically I think you’ll be fine. I don’t know if Flow Kooler publishes any info on their maximum operating rpm, that might be worth checking into. But it looks like they list it for the AC application and the factory had a higher driven ratio so it should be ok.

Same thing for the fan actually, check the maximum rpm if there’s one listed for the fan or the clutch as that’s something you don’t want to exceed.
 
Not sure if it's been pointed out, but another thing to keep in mind is that heat transfer is not linear over time. Generally, the rate of heat transfer is higher with a larger temperature differential between the water and radiator or engine - meaning more cooling is done right when the hot water touches the radiator than when the water is just about to leave the radiator. The more flow you can introduce, the more energy will be pulled out.

Go with the high flow pump.
 
GTX JOHN said:
Restrictor Plates are more commonly used on race cars
that often have high volume electric cooling systems.
They are often on Drag Racing cars that run short periods
and often the goals are to stage at around 100 degrees or
less and complete the run around 120 degrees. I Never advoccated
them on anything but some Drag Race applications.

I have experimented with different drive pulleys (Electric Pumps)
how and observed how the speed of the coolant affects the efficiency
of the cooling process. This is for 50 years and over a career of Drag Racing
and both on and Offroad Racing, not to mention Drift and Slalom. My older
boy has been a Crew Chief on a Pro Drift Team and a Baja 1000 class winner.
Also, he manages one of the major racing experience venues on the west Coast.
Cooling is Paramount on all these venues.

I believe Mopar has engineered the pulley size to be the most effective
for the engine combination. They even had a different water pump with
different vanes for Air Conditioning cars. I am sure that minor changes
in drive speed are irrelevant but to go overboard is ill advised for cooling.one

I may or may not be correct on my posts on this site = but they are honestly
posted from my personal experience with the intent of being of utility to my
friends on this site. If I get enough feedback that they are unwelcome or
misleading = I will be out of here. I have plenty to do in our shop with a dozen race cars
in it.

This is my background/context that I speak from and I am indeed guilty
of being an Old Man.

However, I would not advise you calling me an Old Wife to my face unless
you are on a first name basis with a good dentist (You WILL need one).
Click to expand...

Here- here, well said - sometimes feel you're pissing into the wind.
Bravo .
 
All I can tell you is my experience.

As I stated before = I can only speculate on the why
things occur the way they do. But I can concisely explain to you
WHAT DID HAPPEN in my testing.

I am sure you Engineering boys are way smarter than
I ever was on why and wherefores thing occur with your Pretzel
Logic High School Physics Theories. All I can tell you is what DID
and DID NOT work for in the real world of competitive racing for the last 60+ years.
I am just a Sportsman Racer who races and continuously tests things trying
to get a competitive advantage over my adversaries and never claimed to be
an Engineer.

However, I am always pleased and happy to see an Engineering Type in the
opposite lane to race. Kind of like the two engineers that went Duck hunting.
One shot way high and the other way low but of course the Duck hit the ground
as they had killed it with the average of the two shots.

Looks like no one needs my opinions or advise anymore on
this forum and I am full of Hokum.

I probably should send our 50+ National Event Wallys to
you engineers. Plus our Dozen Track championship Trophies.

I am out of this conversation.

Everyone please send their questions to you learned Gentleman. I obviously
do not have a clue and my experience is clearly and fatally flawed inaccurate
hokum.

I have a half dozen champion Stock and Superstock cars to prepare for the double divisional
and class showdown in Bakersfield next months. I spend way too much time trying to help
people on here than I care to admit. But we will fix that right away.

Overdrive those water pumps double speed and cavitate the crap out of them
until the hoses look like balloons and we will see how they cool!!

BTW: I still stand on all the advice and experiences that I have ever related on this Forum
the last 14 years. I would never send anyone on the wrong track deliberately. Nor relate anything
that I did not have experiences with my own two hands and eyes.

I will be at Sonoma Nationals next year and a Divisional if they have one.
Please feel free to come introduce yourself to me and we will interact in person.


Mark Twain said the last Century: Say anything you like about me = Just be sure
to spell my name right.
 
Last edited:
To Summarize for the final time:

I still stand by my observations that if the water goes thru
the radiator way too fast my car takes way long to cool after the
run down the track especially if you have a stock radiator. Now if it
roared thru the radiator again and again in a loop and never entered the
engine = Perhaps. BUY it does not - It goes straight thru the block look without
near as much cooling which means that it has little ability to cool the engine as it
is NOT much cooler than the engine itself. Less difference in temperature = Less
heat transfered from the engine to the coolant.

Also the Hotter my race car is when I pull in my pits the longer it takes
to cool. The heat may transfer quicker the hotter it. BUT it still take time
to get it down to get to the cooler temp where it transfers slower of course.
But you waste a lot of time to get it from the higher temp to the lower and it
is impossible to recover the wasted time.

Often between passes later in the day in eliminations = The is very little time between rounds
to get your car cooled down and if your car is not consistent you will be putting it on the trailer.

And that is the Facts just the Facts!

Big Fancy Words and Theories not based on real experiences
do not make your car win races or keep
it from overheating at a traffic light. Today it is 110+ in our
town in the shade. but there is NO shade and my Street/Strip cars
(High Compression) cars are cruising right near 160 where the Thermostat
opens are your cars?
 
Last edited:
The water too fast is a an old wives tale, proven wrong time & time again.

What is being missed/ignored is this: if you slow the coolant flow through the rad per the wives tale, then by definition, the coolant that is the engine will be in the engine for a longer time, because it is a closed system. The coolant that has now got hotter from being stalled in the engine arrives at the radiator for cooling, & the rad now has more heat to dissipate.
 
Seems like this should be an easy theory to test using a dyno facility and a controlled environment. Only swapping pulleys between tests. Surely it has been done and proven one way or another.
 
Ok, so I phoned CVF today to get dimensions and drive ratios of the pulleys on their serpentine conversion and the dimensions are as follows:
Crank 6.4"
Water pump 5.3"
This makes the ratio 1.2:1 so will be overdriven. Now I just need to get the combo all sorted out.
I'm thinking of going with the CVF serpentine conversion, 4140063 Mopar fan with Hayden 2947 clutch, Flowkooler water pump and Wizard cooling radiator with their aluminum shroud.
 
Gotta ask a question, if you install the pulleys and pumps, and everything is cooling really good, so good engine runs at 130 - 140 degrees, less in winter, - no heat from the heater, are you going to put a thermostat in to do it's job, and restrict all that flow, - so the engine can come up to operating temp, or run it cold ?
 
inertia said:
Gotta ask a question, if you install the pulleys and pumps, and everything is cooling really good, so good engine runs at 130 - 140 degrees, less in winter, - no heat from the heater, are you going to put a thermostat in to do it's job, and restrict all that flow, - so the engine can come up to operating temp, or run it cold ?
Click to expand...
Absolutely! I forgot to add that I will be using a high flow 180 degree thermostat. The one I have currently is the Mr. Gasket 180 degree high flow all brass construction
 
GTX JOHN said:
All I can tell you is my experience.

As I stated before = I can only speculate on the why
things occur the way they do. But I can concisely explain to you
WHAT DID HAPPEN in my testing.

I am sure you Engineering boys are way smarter than
I ever was on why and wherefores thing occur with your Pretzel
Logic High School Physics Theories. All I can tell you is what DID
and DID NOT work for in the real world of competitive racing for the last 60+ years.
I am just a Sportsman Racer who races and continuously tests things trying
to get a competitive advantage over my adversaries and never claimed to be
an Engineer.

However, I am always pleased and happy to see an Engineering Type in the
opposite lane to race. Kind of like the two engineers that went Duck hunting.
One shot way high and the other way low but of course the Duck hit the ground
as they had killed it with the average of the two shots.

Looks like no one needs my opinions or advise anymore on
this forum and I am full of Hokum.

I probably should send our 50+ National Event Wallys to
you engineers. Plus our Dozen Track championship Trophies.

I am out of this conversation.

Everyone please send their questions to you learned Gentleman. I obviously
do not have a clue and my experience is clearly and fatally flawed inaccurate
hokum.

I have a half dozen champion Stock and Superstock cars to prepare for the double divisional
and class showdown in Bakersfield next months. I spend way too much time trying to help
people on here than I care to admit. But we will fix that right away.

Overdrive those water pumps double speed and cavitate the crap out of them
until the hoses look like balloons and we will see how they cool!!

BTW: I still stand on all the advice and experiences that I have ever related on this Forum
the last 14 years. I would never send anyone on the wrong track deliberately. Nor relate anything
that I did not have experiences with my own two hands and eyes.

I will be at Sonoma Nationals next year and a Divisional if they have one.
Please feel free to come introduce yourself to me and we will interact in person.


Mark Twain said the last Century: Say anything you like about me = Just be sure
to spell my name right.
Click to expand...

GTX JOHN said:
To Summarize for the final time:

I still stand by my observations that if the water goes thru
the radiator way too fast my car takes way long to cool after the
run down the track especially if you have a stock radiator. Now if it
roared thru the radiator again and again in a loop and never entered the
engine = Perhaps. BUY it does not - It goes straight thru the block look without
near as much cooling which means that it has little ability to cool the engine as it
is NOT much cooler than the engine itself. Less difference in temperature = Less
heat transfered from the engine to the coolant.

Also the Hotter my race car is when I pull in my pits the longer it takes
to cool. The heat may transfer quicker the hotter it. BUT it still take time
to get it down to get to the cooler temp where it transfers slower of course.
But you waste a lot of time to get it from the higher temp to the lower and it
is impossible to recover the wasted time.

Often between passes later in the day in eliminations = The is very little time between rounds
to get your car cooled down and if your car is not consistent you will be putting it on the trailer.

And that is the Facts just the Facts!

Big Fancy Words and Theories not based on real experiences
do not make your car win races or keep
it from overheating at a traffic light. Today it is 110+ in our
town in the shade. but there is NO shade and my Street/Strip cars
(High Compression) cars are cruising right near 160 where the Thermostat
opens are your cars?
Click to expand...

I never questioned your experience, I'm sure you saw the results you saw. But that doesn't mean you're right about the problem.

Have you ever actually measured the coolant velocity in your radiator before and after changing the pulley diameter? Have you measured the output GPM of the water pump on your engine before and after changing the pulley diameter? Or even the actual water pump GPM's as installed on your car? Because the manufacture spec isn't what you're actually getting most of the time.

The problem is this- just because you observed a change in your cooling performance doesn't mean the culprit was circulating the water too fast (it wasn't). Just because you changed the ratio on your pulley by 20% doesn't mean the coolant velocity went up 20%. It honestly doesn't mean it changed at all, you could have just reduced the efficiency of your water pump that much by spinning it at a speed it's less efficient at. That's probably not 100% of the difference, there are a TON of variables in a cooling system that are all effected when you change something like that.

You mentioned electric pumps too, which are an entirely different issue. As in, just because you installed a bigger electric pump doesn't mean you increased output. If your electric system can't deliver enough amperage to the pump you may not get any improvement in output at all.

That's the problem with anecdotal evidence. I'm sure you did observe the results you saw. But if you didn't actually measure the flow velocity, and made sure that the flow velocity was the ONLY change, well, you haven't proven anything. You probably changed a handful of variables all at the same time and blamed something you think you understand for the difference. The reality is you had a completely different issue that you didn't understand, and accidentally solved it by throwing different parts at it.

What you did worked, but the reason is not what you think. Circulating water too fast through the radiator is an old wives tale. It's simply not the issue. Which is not the same as saying you didn't have an issue, or that you didn't fix it. I'm positive you had/did both, but the actual reason is not at all what you said it is.
 
This is where book smarts and theory crash head-on with actual experience and reality .
In theory by the smartest folks on the planet, in their field, thought the Stage seal was good, the Challenger's crew experience proved different .
 
Last edited:
inertia said:
This is where book smarts and theory crash head-on with actual experience and reality .
In theory by the smartest folks on the planet, in their field, thought the Stage seal was good, the Challenger's crew experience proved different .
Click to expand...

Uh, no. The engineers on the ground knew the seal was susceptible to failures with cold temperatures. They made their concerns known, and the admin types up the chain didn’t call the launch because of all the media attention. The “smartest folks on the planet” wanted to scrub that launch.

Trying to use that example perfectly demonstrates how you can look dumb if you make assumptions about things without actually understanding them.
 
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