Miks15
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| posted on 27/2/10 at 12:14 PM |
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slowing down the water pump -effects?
Hi guys,
Would it cause any problems if i slowed down the water pump on the car a tad? Basically i have two pulleys which fit on the crank (they were both on
there but one drove the PAS pump).
I only need one pulley (will drive both water pump and alternator)
To get a good size trigger wheel it would be better if i used the PAS pulley, but this is smaller than the normal water pump pulley. (water pump
pulley is about 150mm diameter whereas the smaller one is about 120mm)
Will this cause any problems in the future?
Cheers
Mikkel
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britishtrident
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| posted on 27/2/10 at 12:16 PM |
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Might actually be beneficial for cooling at high RPM.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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sebastiaan
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| posted on 27/2/10 at 12:34 PM |
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And might cause problems when stuck in traffic due to too low coolant flow. It all depends largely on rad, fan, shrouding etc. I'd just try it
and see what happens.
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Miks15
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| posted on 27/2/10 at 12:56 PM |
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well i thought that, but then i thought that i wont have a heater matrix , and the rads closer and smaller, so there wont be as much water to push
around so it might counteract the effects of slowing it down?
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DRC INDY 7
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| posted on 27/2/10 at 01:11 PM |
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it could cause cavitation
https://www.facebook.com/groups/462610273778799/
Puddle Dodgers Club
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SPYDER
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| posted on 27/2/10 at 01:15 PM |
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Fairly standard practice on race cars. We did it on our racing TR's with no ill effects.
As long as you have a sufficiently efficient cooling fan there shouldn't be a problem.
You're not slowing it down that much anyway.
Geoff.
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Miks15
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| posted on 27/2/10 at 01:37 PM |
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sweet, cheers guys, will definatly do that then, will get the trigger wheel ordered now im home,
and hopefully next time im back, ill have this thing running 
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Nash
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| posted on 27/2/10 at 01:50 PM |
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quote:
Originally posted by DRC INDY 7
it could cause cavitation
Why would it cause cavitation?
.....Neil
It's What You Do Next That Counts.
Build It, Buy It, Drive It:
Southern Kit Car Club
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rusty nuts
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| posted on 27/2/10 at 01:56 PM |
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It's less likely to suffer cavitation!!
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Miks15
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| posted on 27/2/10 at 02:16 PM |
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me possibly being stupid...
whats cavitation?
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Dusty
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| posted on 27/2/10 at 03:04 PM |
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It's when you eat too many sweeties and your teeth go bad.
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MakeEverything
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| posted on 27/2/10 at 03:11 PM |
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quote:
Originally posted by Miks15
me possibly being stupid...
whats cavitation?
Where the impellerspins so fast it "Whips" the water rather than causing it to flow.Cavitation has the adverse affect and slows or even
stops the flow. The governing factors of cavitation are pitch of impeller, and speed. Fast is not always best.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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Miks15
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| posted on 27/2/10 at 03:19 PM |
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so by slowing it down it wont increase the chances then,
I think im just going to try with the new pulley and hope it works (cant see any reason it wont, especially not after whats been said)
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daviep
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| posted on 27/2/10 at 03:21 PM |
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Cavitation is when the demand of the pump exceeds the available supply, the pump will draw a vacuum and gas will be drawn out of the liquid. At the
discharge side of the pump the the bubbles of gas implode causing metal erosion.
That' my understanding anyway.
Davie
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britishtrident
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| posted on 27/2/10 at 03:57 PM |
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quote:
Originally posted by daviep
Cavitation is when the demand of the pump exceeds the available supply, the pump will draw a vacuum and gas will be drawn out of the liquid. At the
discharge side of the pump the the bubbles of gas implode causing metal erosion.
That' my understanding anyway.
Davie
Yep thats it, the effect on the impeller is a bit like sand-blasting
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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MakeEverything
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| posted on 27/2/10 at 05:07 PM |
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Fluid Dynamics;
"Discharge cavitation occurs when the pump discharge pressure is extremely high, normally occurring in a pump that is running at less than 10%
of its best efficiency point. The high discharge pressure causes the majority of the fluid to circulate inside the pump instead of being allowed to
flow out the discharge. As the liquid flows around the impeller, it must pass through the small clearance between the impeller and the pump housing at
extremely high velocity. This velocity causes a vacuum to develop at the housing wall (similar to what occurs in a venturi), which turns the liquid
into a vapor. A pump that has been operating under these conditions shows premature wear of the impeller vane tips and the pump housing. In addition,
due to the high pressure conditions, premature failure of the pump's mechanical seal and bearings can be expected. Under extreme conditions,
this can break the impeller shaft."
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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dhutch
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| posted on 27/2/10 at 06:24 PM |
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quote:
Originally posted by daviep
Cavitation is when the demand of the pump exceeds the available supply, the pump will draw a vacuum and gas will be drawn out of the liquid. At the
discharge side of the pump the the bubbles of gas implode causing metal erosion.
That' my understanding anyway.
Davie
Sounds good to me.
- As said, its the drawing of the fluid into a gas by applying a vacuum.
Bad becuase they the pumps spining in
air/froth and becuase of the violence of the gas collapsing into liquid again.
http://en.wikipedia.org/wiki/Cavitation
Daniel
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matt_gsxr
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| posted on 27/2/10 at 07:14 PM |
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Just one thought.
According to the Graham Bell book on 4-stroke tuning. One of the things that stops localised boiling is the pressure of the water (we knew that). He
claims that the water pressure from the water pump is the dominant source of pressure (in the block) I can't remember what pressures he claims.
He does know his stuff, but his book is a bit v8 centric.
Slowing the pump would decrease the pressure and hence could lead to localised boiling (and hot spots).
I guess it must depend on the engine. Loads of people run bike engines with electric Davies Craig pumps, that are variable speed, so on those engines
it can't matter.
Also the book is talking about engines that have been tuned to the last possible bhp, so this is probably not relevant.
Just a thought,
Matt
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britishtrident
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| posted on 27/2/10 at 08:16 PM |
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quote:
Originally posted by matt_gsxr
Just one thought.
According to the Graham Bell book on 4-stroke tuning. One of the things that stops localised boiling is the pressure of the water (we knew that). He
claims that the water pressure from the water pump is the dominant source of pressure (in the block) I can't remember what pressures he claims.
He does know his stuff, but his book is a bit v8 centric.
Slowing the pump would decrease the pressure and hence could lead to localised boiling (and hot spots).
I guess it must depend on the engine. Loads of people run bike engines with electric Davies Craig pumps, that are variable speed, so on those engines
it can't matter.
Also the book is talking about engines that have been tuned to the last possible bhp, so this is probably not relevant.
Just a thought,
Matt
I think that is perhaps looking at it the wrong way round what stops localised boiling in the engine is flow both in terms of mass flow and flow
velocity. The effect of coolant mass flow is pretty obvious while flow velocity generates turbulence which encourages mixing in the boundary layers
on the hot engine surfaces improving heat transfer.
The few psi pressure generated by the water pump is only in reponse to the radiators resistance to coolant flow.
Back in the 1960s and 70s through the early 1980s most car coolings systems only operated at around 7 to 9psi ( 0.5 bar) gauge, these days 21psi
(1.5 bar ) gauge is more typical.
Getting back to cavitation; Cavitation isn't like plain localised boiling it is the flashing off of water molecules on the impeller surface
into highly superheat steam, in effect a micro explosion.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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bimbleuk
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| posted on 28/2/10 at 05:45 AM |
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quote:
Originally posted by matt_gsxrAccording to the Graham Bell book on 4-stroke tuning. One of the things that stops localised boiling is
the pressure of the water (we knew that). He claims that the water pressure from the water pump is the dominant source of pressure (in the block) I
can't remember what pressures he claims. He does know his stuff, but his book is a bit v8 centric.
Though I've read most of his books, on this matter I have to disagree from my observations.
The water pump does provide some mechanical pressurisation but I've run both aqeuos and non-aqeous coolant in my car with the same setup. The
water/ethanol mix runs at about a bar as normal. The non-aqeous coolant makes probably 3 psi at most. Which meant I could take the pressure cap off at
any time and not suffer a face full of scolding water.
The non-aqeous coolant should reduce both local pressurisation and cavitation due to a very high boiling point. I haven't run a reduced pump
speed though with the non-aqeuous coolant myself yet.
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matt_gsxr
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| posted on 28/2/10 at 10:33 AM |
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I was only quoting, and will quote further:
Four-Stroke Performance Tuning
A.G.Bell 3rd Edition
p.433-4
"
Water pump considerations
However, when water pump speed increases to the peak efficiency speed of 4-6krpm it is not the radiator cap that stops boiling but water pressure
created by the water pump. Even many race engine tuners do not seem to understand that regardless of the radiator cap pressure a water pump spinning
at maximum efficiency rpm will produce a pressure head of around 30-40psi in the engine block and head when water flow out of the head is limited by
thermostat or restrictor plate. This pressure packs coolant around the top of the cylinders and around combustion chambers to carry away combustion
heat and stop an insulating blanket of gas bubbles forming in these areas."
If you want to read the rest then buy the book!
He also goes on to say that he does under-drive the pumps sometimes, although this is all relative to the "maximum efficiency zone of
4-6krpm" I doubt you know that for your pump.
I like the book, I can't say his physics is up to scratch. For example in the introduction he says:
"Take the laws of gravity or the day/night cycle as the earth rotates around the sun."*
Which didn't inspire confidence. But he is good at citing evidence of doing things which I like.
Matt
*Obviously the earth rotates on its own axis causing the day night cycle. Rotation around the sun takes a year!
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britishtrident
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| posted on 28/2/10 at 12:24 PM |
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quote:
Originally posted by matt_gsxr
I was only quoting, and will quote further:
Four-Stroke Performance Tuning
A.G.Bell 3rd Edition
p.433-4
"
Water pump considerations
However, when water pump speed increases to the peak efficiency speed of 4-6krpm it is not the radiator cap that stops boiling but water pressure
created by the water pump. Even many race engine tuners do not seem to understand that regardless of the radiator cap pressure a water pump spinning
at maximum efficiency rpm will produce a pressure head of around 30-40psi in the engine block and head when water flow out of the head is limited by
thermostat or restrictor plate. This pressure packs coolant around the top of the cylinders and around combustion chambers to carry away combustion
heat and stop an insulating blanket of gas bubbles forming in these areas."
If you want to read the rest then buy the book!
He also goes on to say that he does under-drive the pumps sometimes, although this is all relative to the "maximum efficiency zone of
4-6krpm" I doubt you know that for your pump.
I like the book, I can't say his physics is up to scratch. For example in the introduction he says:
"Take the laws of gravity or the day/night cycle as the earth rotates around the sun."*
Which didn't inspire confidence. But he is good at citing evidence of doing things which I like.
Matt
*Obviously the earth rotates on its own axis causing the day night cycle. Rotation around the sun takes a year!
Absolute Balderdash
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Strontium Dog
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| posted on 28/2/10 at 12:37 PM |
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Of course you could always bin the pump and use an electric item to feed via a fanimold into the core plug holes! Lots of advantages if you have the
time and engineering skills!
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matt_gsxr
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| posted on 28/2/10 at 01:09 PM |
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quote:
Originally posted by britishtrident
Absolute Balderdash
Thanks ;-)
Matt
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britishtrident
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| posted on 28/2/10 at 01:17 PM |
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40 psi from car water pump --- had me rolling about the floor.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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