Gas Engine cavitation

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Cavitation was an issue in the 70's and 80's with predominantly American V-8 motors capable of turning up to and past 8000rpm. So a few companies used special water pump impellers and larger volume casting or you could convert to an electric driven water pump to cure the problem. Also slowing down the water pump impellers with larger diameter pulleys helped.
*One of the DIY fixes was to attach a plate on the impeller.
The newer engineered block and heads pretty much have illuminated cavitation. There has been some forums with members talking about this happening but when you read all the info at everything posted it is not the cavitation that is the cooling control issue but other factors. I did also read here and there some factory performance model vehicles with high horsepower V-8 engines mention cavitation in the cooling system but these reports are also engines that are running at the extreme engine speeds and some for a length of time. On a street driven engine I fail to see the problem and big concerns but it makes for a good thread conversation?

REDUCTION PULLEYS on mechanical water pumps and pulley driven alternators DO NOT INCREASE HORSEPOWER OR TORQUE.

*Here is a part that was often used to correct people that suspected cavitation. This NIB part is likely older then some member have had their drivers license. I had to dig in my junk draw to find it. LOL
 

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PaxilPlease

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Cavitation was an issue in the 70's and 80's with predominantly American V-8 motors capable of turning up to and past 8000rpm. So a few companies used special water pump impellers and larger volume casting or you could convert to an electric driven water pump to cure the problem. Also slowing down the water pump impellers with larger diameter pulleys helped.
*One of the DIY fixes was to attach a plate on the impeller.
The newer engineered block and heads pretty much have illuminated cavitation. There has been some forums with members talking about this happening but when you read all the info at everything posted it is not the cavitation that is the cooling control issue but other factors. I did also read here and there some factory performance model vehicles with high horsepower V-8 engines mention cavitation in the cooling system but these reports are also engines that are running at the extreme engine speeds and some for a length of time. On a street driven engine I fail to see the problem and big concerns but it makes for a good thread conversation?

REDUCTION PULLEYS on mechanical water pumps and pulley driven alternators DO NOT INCREASE HORSEPOWER OR TORQUE.

*Here is a part that was often used to correct people that suspected cavitation. This NIB part is likely older then some member have had their drivers license. I had to dig in my junk draw to find it. LOL
Nitro: Thank you for the thoughtful and informative response. This is in contrast to the knee jerk and poorly informed responses.
 
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Nitro: Thank you for the thoughtful and informative response. This is in contrast to the knee jerk and poorly informed responses.
The only thing I questioned was why you drill a hole in the cap. But if you got positive results then it worked for you! I often get criticized by some of the things I do and they generally come from people that NEVER experimented themselves with a theory or an idea for improving something on their vehicle to increase its performance or reliability.
Here is my thread check out my modified drinking water bottle as an example of wild idea's not in the mainstream line of thinking. LOL
I say keep up your experimenting to find project and problem solutions that work for you personally.
 
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... REDUCTION PULLEYS on mechanical water pumps and pulley driven alternators DO NOT INCREASE HORSEPOWER OR TORQUE.
So what makes you say this?

I installed underdriven pulleys on the Cobra V8 in my Panoz Roadster, and it made +8 RWHP on the dyno. Before/after runs corrected for temperature, pressure, humidity. It was only about a 3% improvement, but enough to be consistently measurable.
 
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So what makes you say this?

I installed underdriven pulleys on the Cobra V8 in my Panoz Roadster, and it made +8 RWHP on the dyno. Before/after runs corrected for temperature, pressure, humidity. It was only about a 3% improvement, but enough to be consistently measurable.
Reductions Pulleys or lighter pullies do not increase the horse power. (the exception is on a Supercharger that you are increasing the rotor speed for a specific vehicle speed) The engines power is developed through the exhaust, intake and fueling system. I would say contact whom you got your DYNO testing done and they can explain to you exactly where your power gain was if it really was and not simply that the DELTA were different from the testing before and after the pullies were installed. Or post the DYNO sheet without any SAE smoothing both test before and after with all the DYNO set up and operating information pertaining to your testing.
Example: if I have an engine on a stand with no accessories and do a dyno test it will show x= Horse power power xt= engine torque. If I add an alternator now I have parasitic drag and both X and Xt will be lower. Changing the pulley smaller or lighter results in the same x and xt but possibly in some example at a different RPM range. So reduction pulley will support the engine output and can change where the power level is but DOES NOT INCREASE an engines output .
This has been a misconception since the late 70's when performance parts manufactures cleverly advertised implying that reduction pullies will gain you engine power.
If it were only that easy.....LOL


I must also add that I owned 3 types of Dyno's in my business and have conducted 100's of Dyno testing and fun runs over the years.
1x Engine Dyno
1x Chassis Dyno shop
1x Portable Dyno for vehicle and show events
 
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It takes power to spin the water pump. It takes less power to spin it slower. So with underdriven pulleys, the engine is making the same power, but less of that power is being used to drive the water pump, which is more power delivered to the wheels.
 
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It takes power to spin the water pump. It takes less power to spin it slower. So with underdriven pulleys, the engine is making the same power, but less of that power is being used to drive the water pump, which is more power delivered to the wheels.
But wouldn't you size the pulley as part of an overall assessment of the engine cooling requirements and specific pump output? Are you saying you'd arbitrarily underdrive the pump to save power without knowing the repercussions?
 
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It takes power to spin the water pump. It takes less power to spin it slower. So with underdriven pulleys, the engine is making the same power, but less of that power is being used to drive the water pump, which is more power delivered to the wheels.
LOL I gave my explanation based on my personal experience and suggested that you talk to your DYNO operator. Please show them what I said.

Or contact a Performance Engine Machine shop and tell them your street wise theory of power parts? ;)
 
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But wouldn't you size the pulley as part of an overall assessment of the engine cooling requirements and specific pump output? Are you saying you'd arbitrarily underdrive the pump to save power without knowing the repercussions?
Yes you are on the right path.... Most companies that have performance water pumps or offer reduction and light weight pullies generally all say "and worded somewhat like.. "supports engine power" or "save engine power" . Water pumps when they start spinning to fast and before they cavate water also produce a measurable drag on the engine power, so slowing them down helps maintain the engine power at a chosen RPM range . But it is a careful balance between slowing the water pump down and not losing coolant flow which could raise the coolant temperatures.
 
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But wouldn't you size the pulley as part of an overall assessment of the engine cooling requirements and specific pump output? Are you saying you'd arbitrarily underdrive the pump to save power without knowing the repercussions?
The way you phrase your question, it answers itself: of course not.

However, the original cooling requirements might not match your application. Hypothetical example: you may have an engine with a wide RPM range, say 600 RPM idle and 8,000 RPM redline, where the manufacturer decided to use a pulley ratio that gives adequate flow at idle but spins so fast it cavitates above 6,000 RPM. Perhaps they did this because they optimized it for typical pragmatic street driving: owners who spend more time idling in stop & go traffic and hardly ever revs above 6k, and then only for fractions of a second. In this case, if you don't drive in traffic but you do wring out the engine at high RPM, underdriving the pulleys is actually better for the engine.

Pragmatically speaking, at mid to high RPM the water pump spins fast enough to provide adequate flow through a broad RPM range, so slowing down 25% or some reasonable fraction won't make any appreciable difference in cooling.
 
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Nice theory but you are leaving out CFM of the flow rates. If you are going to talk about impeller speeds then please include this. And where in the world did you get the information about how a Power Train engineering and development depart in an auto manufactures use what you said to determine a water pump design??

I am surprised given you are in SCCA and I presume spent time in events and around people that actually build cars and engines for competition?


On a couple of my NHRA Race cars I use electric drive water pumps and also on one of my street cars I use an auxiliary electric driven water pump for extra cooling control in warm or hot operating environments. When used it will increase the CFM of coolant at lower vehicle speeds and controlling the coolant temperatures which also effect the EGT's and oil temperature's all resulting in a more reliable and predictable power output. BUT .... They DON'T increase the power of the engine only SUPPORT the engine power?
 
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.... They DON'T increase the power of the engine only SUPPORT the engine power? ...
Water pumps when they start spinning to fast and before they cavate water also produce a measurable drag on the engine power, so slowing them down helps maintain the engine power at a chosen RPM range .
You keep misreading what I'm saying. I agree with your second statement above, that has been my point all along.
At the end of the day, RWHP is what matters as that is what moves the car. You can get it by increasing the engine's power output, or by reducing parasitic drag on the engine.
 
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You keep misreading what I'm saying. I agree with your second statement above, that has been my point all along.
At the end of the day, RWHP is what matters as that is what moves the car. You can get it by increasing the engine's power output, or by reducing parasitic drag on the engine.
Ha! I dont exactly see that.. but ok? 🤪

I like most of your responses on several threads so please don't take my response personal there are just a few topic's that maybe in my field of experience on a professional level regarding not a DIY?

You remind me of debating with my flight training instructor around 1977...
My instructor tried to teach me that all encumbering 50foot obstacle during final approach. The book work and practicing on a theoretical object landing I always debated with my instructor about the physic's of gravity. LOL Then one fine perfectly clear sunny day no clouds 1 mph cross wind I was landing at Nut Tree and there is was the trees on final approach but 75feet you had to clear and drop quickly not to over shoot. Well I cleared the obstacle came in with a bit to much speed (puddle jumper if thats even possible lol ) over shot right off the tarmac , off the gravel and in to the field stuck the gear in soft mud compounded by cows really working it over making it a mud soup and flip over in what I thought was so slow I think I could have unbuckled and claimed in the rear to counter the weigh and not end up upside down with mud on my face so to say when the insurance company did the investigation into the accident. LOL
 
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... one fine perfectly clear sunny day no clouds 1 mph cross wind I was landing at Nut Tree and there is was the trees on final approach but 75feet you had to clear and drop quickly not to over shoot. ...
As you probably know, that's the perfect application for the forward slip. And why that maneuver is part of the PTS.
 
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I repaired diesel generators for many years. When doing overhauls, I sometimes found erosion on always the same side of the cylinder liners when I pulled them from the block. It was curious enough to make me want to learn about it.
Turns out, as the pistons move up and down, the side thrust would flex the liner wall…. We’re talking microscopic amounts. This slight movement causes the coolant to move away and crash back as the liner wall relaxes. This is all on the coolant side of the liner. I’ve seen slowed down x ray videos of this. It’s crazy. I’ve even seen engines that didn’t receive the best care actually wear through and leak coolant into the crankcase.
Coolant additives that promote adhesion fight this as does cleanliness and the proper pressure.
I always run a bottle of Redline Water Wetter in my vehicles. Never had a problem.
 
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I repaired diesel generators for many years. When doing overhauls, I sometimes found erosion on always the same side of the cylinder liners when I pulled them from the block. It was curious enough to make me want to learn about it.
Turns out, as the pistons move up and down, the side thrust would flex the liner wall…. We’re talking microscopic amounts. This slight movement causes the coolant to move away and crash back as the liner wall relaxes. This is all on the coolant side of the liner. I’ve seen slowed down x ray videos of this. It’s crazy. I’ve even seen engines that didn’t receive the best care actually wear through and leak coolant into the crankcase.
Coolant additives that promote adhesion fight this as does cleanliness and the proper pressure.
I always run a bottle of Redline Water Wetter in my vehicles. Never had a problem.
Nice read NYEngineer (y)
I thought all well equipped DIY garages has it? :D
 

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Astro14

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There is enough bickering and braggadocio in this thread to drown out any further reasonable discussion.
 
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