Sparkie
Posted 10 July 2013 - 02:21 PM
What you have to remember is when the SPI/MPI evolution started the world became obsessed with emissions, back in the 70/80 a single cam Nova/Astra engine was over 80bhp and went very well and revved out, now we have 16v twin cams which are not allowed to have any fuel and they flatten off after 4000rpm .
Back on topic if you could gain 5bhp over a competitor thats could be the difference between 1st and 2nd and engine driven fans are drawing power all the time, unlike a electric.
Mini Mad
Posted 10 July 2013 - 03:46 PM
In a competition environment, it could make a difference. The difference it will make will be a % of power I would have thought, rather than a set bhp figure.
I.e. on a 100bhp 1380 @ 6500, you might get 4/5bhp from removing the fan. On a 45bhp 998 @ 6500, I doubt you'd get anywhere near that gain - probably 1-2bhp, if that.
As said above Spi/Mpi isn't a good comparison - they are completely different fuel and ignition systems which could affect power output.
I still keep considering using an electric fan instead of the mechanical fan. Reasons:
- Even with the electric fan running, at higher RPM I reckon the alternator would be less drag on the engine than a mechanical fan. A fan will draw ~15A. A good set of headlamps and spotlamps will probably draw the same, which I doubt saps as much power as physically turning a fan at high RPM.
- Economy. I have always found my Mini to run too cool. On a cold morning it takes too long to get up to operating temp - if it does actually get to proper operating temp - usually it doesn't even get past a quarter. I have a 92 stat, and the rad side of the grille blocked off. In this weather it's running LOADS better, and giving more MPG aswell - and the temp gauge stays consistently around halfway point (still with 92 stat and rad blocked).
I think you are more likely to notice a few more MPG from the consistent engine temps than the extra power.
Uncle Cooperman, Voted Mr TMF 2011
Posted 10 July 2013 - 05:53 PM
Yes, an electric fan could 'use' 4 bhp, but it will only need to be on ocassionally and modern fans are much more efficientI 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.
Crazy About Mini's
Posted 10 July 2013 - 06:48 PM
Up Into Fourth
Posted 10 July 2013 - 10:16 PM
Fair enough, but I have a reasonably standard 998 and a fan mounted on the outside of the inner wing from a Golf TDI that when on low speed draws about 6 amps and high speed draws 14 amps, which relates to 0.2BHP (on high speed). We also made out of some mudflap, cowling that goes down the sides and along the top to ensure the majority of the air is drawn through the radiatorOn a Mini with a side mounted radiator the fan needs to be on all the time, in other words a 100% duty cycle.Yes, an electric fan could 'use' 4 bhp, but it will only need to be on ocassionally and modern fans are much more efficientI 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.
removing the fan on a road mini to gain a couple of bhp, which will probably never be noticed in public road driving is a big risk with a Mini. All the extra power possibly gained is no use if you are sitting by the side of the road having blown all the water out.
TMF fantasy F1 winner 2012
Posted 10 July 2013 - 11:55 PM
The difference it will make will be a % of power I would have thought, rather than a set bhp figure
I.e. on a 100bhp 1380 @ 6500, you might get 4/5bhp from removing the fan. On a 45bhp 998 @ 6500, I doubt you'd get anywhere near that gain - probably 1-2bhp, if that.
The power lost would be the same, it would not be a percentage. The fan would be moving the same amount of air, thus doing the same amount of work, thus requiring the same amount of power to move the air.
..is NOT a girl!
Posted 11 July 2013 - 12:09 AM
True, except for any differences in pulley size,if that's crank rpm. It'd be interesting, but way too complex to measure, what difference the force of natural airflow through the grille makes. I'm sure, having fitted an auxiliary leccy fan under the wing, that Rover would have left off the belt driven one if it was feasible.
TMF Mug
Posted 11 July 2013 - 12:11 AM
Its a mini engine....5bhp isnt nothing to worry about...
TMF fantasy F1 winner 2012
Posted 11 July 2013 - 12:23 AM
If you change the pulley sizes then it will affect the power used by the fan, it will also change the volume of air moved by the fan, and thus alter the amount of cooling, which could also increase of decrease the engine temperature, and thus change the power output of the engine. With no difference in pulley size the fan will use the same amount of power on a 45hp engine and a 100hp engine, it will not be a percentage.
I'm sure this subject was discussed on the forum a few months ago and the conclusion was that, for a road going car with a side mounted radiator, having just an electric fan was not a good idea. It would be likely that the fan would run permanently as there is not enough airflow through the grille and out into the inner wing to cool the coolant without the fan running. Hence why Rover fitted both the mechanical and electric fans, the electric fan helping in slow traffic when the engine speed and fan speed are too low to produce sufficient air flow for cooling the coolant.
Camshaft & Stage Two Head
Posted 11 July 2013 - 01:00 AM
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.....
Oh if only it were so simple. I'm afraid it's much more complicated than cross section cutting through the air.
Camshaft & Stage Two Head
Posted 11 July 2013 - 01:07 AM
In a competition environment, it could make a difference. The difference it will make will be a % of power I would have thought, rather than a set bhp figure.
I.e. on a 100bhp 1380 @ 6500, you might get 4/5bhp from removing the fan. On a 45bhp 998 @ 6500, I doubt you'd get anywhere near that gain - probably 1-2bhp, if that.
As said above Spi/Mpi isn't a good comparison - they are completely different fuel and ignition systems which could affect power output.
I still keep considering using an electric fan instead of the mechanical fan. Reasons:
- Even with the electric fan running, at higher RPM I reckon the alternator would be less drag on the engine than a mechanical fan. A fan will draw ~15A. A good set of headlamps and spotlamps will probably draw the same, which I doubt saps as much power as physically turning a fan at high RPM.
- Economy. I have always found my Mini to run too cool. On a cold morning it takes too long to get up to operating temp - if it does actually get to proper operating temp - usually it doesn't even get past a quarter. I have a 92 stat, and the rad side of the grille blocked off. In this weather it's running LOADS better, and giving more MPG aswell - and the temp gauge stays consistently around halfway point (still with 92 stat and rad blocked).
I think you are more likely to notice a few more MPG from the consistent engine temps than the extra power.
If you're really interested in this - google "fan affinity laws".
In short:-
Increase a fan runner speed by 10% and
The volume of air shifted will increase by 10%
The pressure head increases by 21%
And what you are all asking about.....the power will increase by 33%
Double the speed....4 times the power.
Camshaft & Stage Two Head
Posted 11 July 2013 - 06:47 AM
If the mass of the fan causes power sap.........Has anyone developed a lightweight carbon fibre fan?
Mini Mad
Posted 11 July 2013 - 01:10 PM
If the mass of the fan causes power sap.........Has anyone developed a lightweight carbon fibre fan?
I would have thought it was more the drag of the fan moving through the air which saps the most power.
..is NOT a girl!
Posted 11 July 2013 - 01:24 PM
The mass would only matter under acceleration, the same as a flywheel.
I'm intrigued by Capt M's "double speed, quadruple power" wouldn't it be the same as drag on the car? You're accelerating the air twice as fast, but you're also doing it to twice as much air, so the increase should be cubic - excepting any changes in efficiency.
Camshaft & Stage Two Head
Posted 11 July 2013 - 01:54 PM
If the mass of the fan causes power sap.........Has anyone developed a lightweight carbon fibre fan?
I would have thought it was more the drag of the fan moving through the air which saps the most power.
Exactly what i thought.....and said in the first response I made to this post. Then i got shot down by someone who knows what they are talking about....apparently. You really can't win on here.
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