46 replies to this topic

[gould1990]

I was at a mates house the other night with my mini and he was looking at the engine. he said "if you change that to a single blade metal fan you could get about 5BHP" is this true and if so how does this work?

 

i currently got the standard plastic fan on

[Moggyton]

I really dont see how changing the fan would gain you 5 BHP, ive never heard it said before. But i guess its worth waiting for someone that knows to tell you

[rally1380]

Naaaa.....you don't 'gain' power by changing a fan.  Think what your mate was on about it that some fans can sap power from an engine as it takes the engine more effort to spin it.

 

A standard plastic fan is fine and takes alot less 'power' to spin it than say a 6 blade metal fan.

 

Its all about cross sectional area cutting through the air.

 

Sorry for the boring post......now for some more less boring posts.....

[Artful Dodger]

Reduced effort with a fan with less drag:). Reduced effort = more horseys!

[Ethel]

The plastic fan is more efficient because the blades have a proper aerofoil shape.

[mk1monster]

Paint the fan red... sorted

[jagman.2003]

I did read somewhere, it may have even been a Vizard book, that the fan will drag about 4hp. But if you take it off you'll reduce cooling. Then you need to put an electric fan on. This drags the alternator down, probably sapping around 4hp. No real gain. Don't get me wrong if you pinch 4hp here there & everywhere you can it all adds up.

[Carlos W]

There's a lot of things worth considering for power loss other than the fan!

And if you're fan is costing you 5bhp. That's up to 10% of the engines power!

I find that a little hard to believe!

[KernowCooper]

From a article by Vizard this was on a tuned Imp engine.

Removing the fan

Having got the best of what we had so far, a few little experiments seemed to be in order. First of all the fan was removed to see just how much difference this would make to the power output of the engine. Up to 4000rpm the difference was insignificant. At 5000rpm the fanless engine showed two brake more. At 6000 it showed three more; al 6750 it showed 3.8 and by the time it got to 8000 the difference was 5.3bhp. Adding extra radiators or some means of keeping the engine cool whilst disposing of the fan means more performance.

 

 

5.3bhp at 8000rpm so if you can save that then it all adds up

[sonikk4]

Each engine driven ancillary on you engine will sap horsepower to a certain amount.

 

The Americans used to advertise their engines as SAE Gross horsepower which is the power of the engine without ancillaries. 

Then there is SAE Net Horsepower which is the power of the engine plus ancillaries.

 

Now most of it is done as DIN Horsepower which is nearly identical to SAE Net but is something you see now in Europe. Along with with KW's as well.

 

So yes a fan will sap power as will the alternator. The bigger the unit in theory the heavier the loss so yes an electric fan will save you a few horsepower but you may have to increase the size of the alternator so losing power. 

[Ethel]

It's exactly the same as the power to speed ratio of driving the vehicle along the road i.e. cubic.

 

Saving a few hp at race engine speeds isn't much use if your road engine has already overheated. An alternative would be to alter the fan belt pulley sizes, which could also save power by reducing the water pump & alternator speeds. Again, provided they aren't too slow for your usual operating rpm.

 

Some vehicles have  couplings that allow mechanical fans to  "freewheel" to a set output. never seen one on a Mini though (possibly because it'd be the wrong side of the radiator to sense when it's needed), and it'd cost more than a front facing radiator.

 

This looks interesting, though not a direct solution

[Dan]

Its all about cross sectional area cutting through the air.

 

  Not all, it's about the fan's mass too.

 

 

 At 6000 it showed three more; al 6750 it showed 3.8 and by the time it got to 8000 the difference was 5.3bhp. Adding extra radiators or some means of keeping the engine cool whilst disposing of the fan means more performance.

 

 

  Of course increasing the capacity of the cooling system increases the mass of coolant that has to be driven by the pump, increasing the load on the pump and so on the engine which would claim a couple of bhp back.  Also adding loads of radiators and extra coolant adds to the mass of the vehicle reducing performance globally.

 

 

 

Some vehicles have viscous couplings that allow mechanical fans to  "freewheel" at a set output. never seen one on a Mini though, and it'd cost more than a front facing radiator.

 

  Viscous hubs need a large surface area as a heatsink in order to make them work, in the ones I've seen the hub is nearly the size of the entire fan in a Mini.  They also have to be in the hot air flow coming off the radiator.  It would be hard to make one fit a Mini.  The alternative for a Mini was the old Dowty fan, which had articulated blades that feathered themselves off as the engine speed rose.  I have one that used to be fitted to my car, they aren't brilliant.

 

  All in all, the best solution for a Mini is to use the late plastic fan.  There are a few plastic fans, and they aren't all as good as each other, but the later 16 blade ones are fine.  They are very light, move air very well, cost only a couple of bhp to run and are pretty quiet.  If you are that worried about it try to find a mainstream Cooper one, it has thinner blades and will free up a bit more power without causing headaches in other areas that need to be solved.

Edited by Dan, 10 July 2013 - 01:20 PM.

[jonny f]

A simple google would tell you your answer straight away.

 

I saw this article a while back.

 

http://www.kentautod...ng-the-results/

 

Thats minus a mechanical water pump to.

 

I'm going to be running no mechanical fan, just an electric one and a radtec extreme radiator.

[Gremlin]

I did read somewhere, it may have even been a Vizard book, that the fan will drag about 4hp. But if you take it off you'll reduce cooling. Then you need to put an electric fan on. This drags the alternator down, probably sapping around 4hp. No real gain. Don't get me wrong if you pinch 4hp here there & everywhere you can it all adds up.

Yes, an electric fan could 'use' 4 bhp, but it will only need to be on ocassionally and modern fans are much more efficient

[surfblue63]

Here's a little nugget of information regarding BHP and mechanical fans vs electric fans.

 

1275 Spi Cooper quoted BHP is 63. Mechanical fan and side radiator

1275 Mpi Cooper quoted BHP is 63. Electric fan and front mounted radiator.