MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Power to run different fans ?

Here's a thought for the scientific-minded. What would be the power draw difference between a 4 bladed fan and a plastic 7 bladed fan? Stock T series fan verses an MGB fan! PJ
PJ Jennings

Wow, that's a challenge. I fitted the 7 blade fan and gave it a very brief thought, but that is all. In fact I didn't even compare the diameter or the weight, which might both be influencing factors. I doubt it can be calculated at all easily because there are many variables. You might get a very approx idea if you could rotate both at the same speed and compare the volume of air shifted. If the 4 blade fan absorbs 1bhp then you might surmise the 7 blade fan shifts more and absorbs more energy, but maybe not. I doubt it makes any detectable difference to a driver.
If the plastic fan sheds a blade it wont do anything like the same damage as a metal blade (and they do).
Dave H
Dave Hill

I agree with the blade separation causing major damage Dave, in fact I've thought of replacing my old original fan with a new metal one or possibly the plastic one. The blades on the plastic fan are aerodynamically designed which actually makes them more efficient than the old style metal ones and possible make up for the extra drag the addition of three more blades would cause, that's where the scientific minded comes in. I don't have a heating problem, but agree that the seven blade design would be beneficial in hot climates and slow running speeds for a marginal system. PJ

Just spicing things up a bit! LOL
PJ Jennings

Out on the road it might take a bit more power but just think how fast the car will go with a proper propeller pulling it along ------------lol
William Revit

I like the idea of that!
More efficient, very probably, but more air shifted ought to mean more work done so its a complex calculation. Its a Xmas teaser all right.
When I fitted mine I was thinking not just about the water cooling system, but also the alternator in a dynamo case, thinking it might need all the help it can get.
Dave H
Dave Hill

Difference in weight of the two fans I think would also be a determining factor, the plastic fan being much lighter and thus using less HP to turn.

Jim
James Neel

Here is my guesss:
the reason to install an MGB fan is the higher cooling rate. So, the MGB fan will take more power to do so.
To give it some numbers:
A Kenlow electric takes about 20 amps so its capacity is about 300 Watt (which is about 1/2 HP).
Suppose the blow of that Kenlow compares to the MGB output.
So, the blow of the original TD fan will be something like 50-70% of that MGB fan, so about (1/4 - 3/8 HP).
And yes, there will be some efficiency differences between the two fans.
Huib Bruijstens

A lot of assumptions there, but its as good a way of putting some numbers to it as any I think, so well done.
I've read somewhere a proposal that the original fan takes about 1hp, which seems rather a lot looking at your numbers, but I suppose there is the pulley system in addition (not including the generator) plus a certain amount of rounding up.
Dave H
Dave Hill

It's a pity that these old mechanical fans obsorb their maximum power at high speed. When we don't need them !

But original is original. And maybe this lost power remain negligible. Think of what is lost in the gearbox and in the rear axle. They are quite warm. Just feeling the heat after a long run I would say around 1 BHP each.
And finally here is what we can find in "Tuning and maintenance of MGs" by Philip H. Smith, dec 1956 :
"An additional 1 b.h.p. is also available
at maximum revs if the fan blades are removed, this representing the
power absorbed by this component."

Laurent.
LC Laurent31

Indeed so. When I rebuilt my TF, I did not fit the mechanical fan, only a thermostatic electric fan in front of the radiator, trying to maximise the available hp. On starting up the engine for the first time, with no fan running, I was shocked at the amount of smoke generated around the engine. This was all the volatiles - paint solvent, oil, etc., being driven off for the first time. I quickly switched on the electric fan to clear it. Then I also noticed a small weep of fuel from the carb jets, something that I fixed soon after. However it made me realise that having a fan running all the time to drive any fumes away from such a leakage that might occur again was not a bad idea. I put the mechanical fan back on, and upgraded it to the MGB type.
Dave H
Dave Hill

Ha anyone thought of trying to fit a viscous coupled fan?
(Ducks for cover)
C I Twidle

Ha anyone thought of trying to fit a viscous coupled fan?
(Ducks for cover)

Not as bad an idea as one might think, but temp sensing electric fans would be the simplest method and negligible power draw.
PJ Jennings

Back to Paul's original question, "scientifically what's the difference in power?" It boils down to, "how much air is the fan moving?" -- it takes power to move the air, if one fan moves more air it takes more power. The weight or no. of blades makes little difference. The heavier one will take a little more power to bring it up to speed. If more blades make it more efficient, it would make that fan take less power if it moved the same amount of air, but if it moves more air it still will probably take more power.
Al
Al Parker

And at high speed, a pump mounted fan might not be using as much power as may be thought, as the air will be moving backwards at whatever speed the car is being driven forwards.
R WILSON

Not really comparing like with like so it's difficult to tell. If the blades were of the same design then the power requirement and the flow thru the fan would increase up to a point of about 11 blades. But the blades on these two fans are a different design. The performance of the blade depends on it's angle of attack (the twist in the blade) the length of the blade, the diameter of the hub, it's rotational speed and other factors. The MGB fan looks like it may have a more efficient design and be designed to run slower than the T fan to quieten it down. Putting it on a standard T pulley may speed it up which would again take more power. Who knows?

AJ
A R Jones

This thread was discussed between 15/12/2019 and 19/12/2019

MG TD TF 1500 index

This thread is from the archives. Join the live MG TD TF 1500 BBS now