Gent's what is the difference in performance between a 12 vane and 6 vane pump. apart from obviously the amount of vanes.
What is the best one to fit and why??
What is the best one to fit and why??
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At one time it was said the 6 vane is better as it moves more water around than 12 vane but not sure if thats still the general opinion.
Mark
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Spent ages trawling the interweb for this answer at the time. Since decades it has been discussed and no conclusive proof of the advantage of either has been established.
At one time the SOC Technical Committee preferred the 6-vane due to its more aesthetic cover!
If you read the technical reprints on the SOC website (you have, haven't you?
) there is a bit of information about this issue under the cooling system chapter.
Don't forget that the covers are different (and expensive!) and, if you change to 12 vane you will need a 12-Vane cover.
I think I got perhaps the last NOS 6 vane off LD Parts about a year ago.
About a year ago, the tendency was to go for the 6 vane impellor.
The answer isn't 42, it's 1/137Comment
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I'm not sure which one is best, but I have a 12 vane and it seems to do the job perfectly well. I have read somewhere that 6 vane may be better at higer revs I think.
Brian
Drive a Stag every day... it's wonderful!
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Hello,
one of the previous owners of my Stag (not Al Hassiri!) installed a 12 vane impeller into the engine, but used the housing for the 6 vane impeller. The result was a vapour lock in the water pump followed by extreme overheating with all its consequences.
Prof. Matthias Lindner (Stag owner and member of the German SOC) performed tests at the Technical University at mannheim/Germany. If I remember correctly he found out that the 12 vane impeller has about 20% more efficiency.
Stephan Boehmwhoowns aStag garage(http://www.bost-british-oldtimerservice.com/home.html) took part in this research and is currently developing a waterpump, which is a 1:1 replacement of the original one. However the impeller and seals are redesigned and improved. Stephan says that the prototypes are already tested in different cars. He reckons his water pumps will be on the market in about two months. The only problem he is working at at the moment is that his pumps are too (!) effective, as they produce too much pressure when the engine is still cold and working with the "small circulation" (thermostat closed) still.
It will be interesting to see his results.
Have a nice weekend, Dieter - from Germany.
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Historically the 6-vane was supposed to move more water (i thought there was a SOC tech reprint article on this ?)
Given that there are plenty of both configurations around that don't have any cooling problems i would stick with what you have and avoid searching for a new cover which you would need to change if changing from 6 to 12 , or 12 to 6 vane impeller.
..........Andy
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The 6 vane is a better design for a pump impeller, but it's not as simple as that. Pumps are generallydesigned to run at a particular speed and the 6 vane works well at higher revs where it will produce good pressure and hence excellent flow. Unfortunately at low revs itstruggles to shift enough water in the Stag engine.
The 12 vane performs better at low revs because there are double the number of vanes but the tangential design results in it being considerably less efficient at higher revs whereit will tend to churn(NOT cavitate!!!) rather than cut into and pick up thewater from the eye and force it into the volutes.
There is insufficient room to cast 12curved vanes on the impeller as there would be more vane than space to allow the water to flow. Since Stags and Dolomites tended to overheat after a good high speed run when they came to a suddenstop (or even on tickover) the 12 vane suited the easy cheap fix methods adopted by BL at the time.
Anyone that tells us that a 6 vane pump works best in a racing Stag "because it produces less flow allowing the water more time in the radiatorto cool" is talking rubbish.It's better because it produces MORE flow at HIGHER revs. Increased flow will ALWAYS result inbetter cooling.
There seems to be many misunderstandings about the Stag's water pumps, radiators, pressure caps, expansion tanks, header tanks, plumbing, cooling fans etc.and reasons for it not performing.
Which pumpis best? It depends how you drive, around town or open road,if your engine overheats and under what circumstances. Unfortunately there is no right answer IMHO.
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Hi Mark. This topic is interesting to me becuase it is very relevant to all stag owners, and I think it the dynamics are much more complex than 'more flow = more cooling'. My gut feeling is that if you plot temperature vs flow it is a curve with a maximum point somewhere in the middle.Originally posted by Mark S View Post
I have tried several times to model the dynamics to show how flow affects cooling, but, as much as I hate to admit (being an engineer) my 'physics' is not quite up to it. The model as I see it is two heat exchangers, one being the cylinder heads (combustion heat input = constant for simplicity) and the other being the radiator (constant air flow through but heat output may vary with flow), with the only variable being coolant flow. Then if we can get an equation for coolant temperature with flow as a variable we should be able to plot temp vs flow. Anyone?Comment
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Quarter to three.Originally posted by V Mad View PostI only do what the voices in my wife’s head tell me to do!Comment
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Chris, the physics is quite straightforward the greatest heat transfer will occur when the temp difference is the greatest. In the engine this means the temp difference between the coolant and head is the greatest ie the lower the coolant temp the better. In the rad you want the coldest air.
Moving the coolant slowly around the system will mean a lot of the engine is recieving already hot coolant and hence less heat transfer. On the other handmoving slowly thru the rad with the, now hotter coolant will give more heat transfer.
Oh Sod it! what do I care I have an electric water pump and ,as chief engineer Scottie always used to say, "You canna beat the laws of physics!" and then engage warp drive and go faster than the speed of light!
-AlanComment
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Originally posted by alan_thomas View PostChris, the physics is quite straightforward the greatest heat transfer will occur when the temp difference is the greatest. In the engine this means the temp difference between the coolant and head is the greatest ie the lower the coolant temp the better. In the rad you want the coldest air.
Moving the coolant slowly around the system will mean a lot of the engine is recieving already hot coolant and hence less heat transfer. On the other handmoving slowly thru the rad with the, now hotter coolant will give more heat transfer.
Oh Sod it! what do I care I have an electric water pump and ,as chief engineer Scottie always used to say, "You canna beat the laws of physics!" and then engage warp drive and go faster than the speed of light!
-Alan
"Aye, It's a pump Captain - but not as we know it" Scotties Mum.Comment
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Quarter to three? mmm does that compute? Maybe its 42?Comment
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Unfortunatley you cant solve this by a common sense analysis. You could argue that iIf you move the coolant slowly, more heat will be extracted from the coolant in the rad, which leads to a lower coolant temp going into the engine. So which is correct, fast or slow? My guess is neither; there is an optimum flow rate for any given system.Originally posted by alan_thomas View Post
Show me the maths, show me the maths!!Comment
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