911 engine cooling fan: power consumption?

[911hillclimber]

Yes, all RRoad runs with everything connected. Too much fussing to go back and the cost just to find out as I feel sure it cannot be replaced by an electric motor withing the space available.

All those factors plus Driver attitude on the run will have a massive effect on the time of the run way beyond 30 bhp.

The Driver is the biggest variable in the whole package.

[Nine One One]

Go on a crash diet! Less weight more BHP

This on Pelican...........
You will gain, but it's better to think in percentage as opposed to actual values. For instance, 10% power gain can be seen (not exactly but roughly) the same as a 10% weight loss. So if the car had 300 hp and was 3000lbs for instance, a weight loss of 300lbs (which is significant) would be about the same as a 30 hp gain. If you want to think of it more accurately, use proportions (which is how power to weight ratios are figured out) like 3000lbs/300hp would essentially (assuming perfect world variables like gearing) be the same as 2000lbs/200hp. But the thing about wieght loss is that acceleration is just one by product. Deceleration, quicker handling reaction, less stress on brakes for a given amount of deceleration are some of the other advantages.

[RobFrost]

Modern fans are much more efficient than old ones. A high speed turbine type fan with wing-shaped blades rather than the angled type on old 911s, bigger surface area, longer blades and a smaller centre, will probably halve the energy used to drive it. However I don't know how those would perform in driving air through the fins. I wonder if a mister would help you, if allowed by your regulations.

On a related note I recently calculated how much horsepower can be saved by knife-edging a 911 crank. If we assume the case is full of oil mist at atmospheric pressure and not just air, at 6,000 rpm you could save as much as 0.5hp. Although if I recall it goes up with the cube of revs so could be much more on a higher revving engine. I decided it wasn't worth it.

One of the reasons is the very thin webs on the 911 crank, which is a consequence of the boxer design which makes for a short crank and little space in-between con rods for the webs. Air resistance is proportional to cross section.

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[Jonny Hart]

The Singer DLS-T uses a horizontally mounted brushless electric fan. The fan uses around 80A so you would need to run a high power alternator (as you may drag the voltage so low that you enter a rising current / falling voltage 'death spiral'. 80A at 12V is around 1.3 HP so it seems attractive but you wont just be switching this fan 'ON'. You'll need a control loop for temperature regulation of the fan speed and a brushless fan controller. I would budget £2,500 at least for the parts and a whole load of development.

[RobFrost]

The Singer DLS-T uses a horizontally mounted brushless electric fan. The fan uses around 80A so you would need to run a high power alternator (as you may drag the voltage so low that you enter a rising current / falling voltage 'death spiral'. 80A at 12V is around 1.3 HP so it seems attractive but you wont just be switching this fan 'ON'. You'll need a control loop for temperature regulation of the fan speed and a brushless fan controller. I would budget £2,500 at least for the parts and a whole load of development.

Given the way the car is used, two speeds with a manual switch would probably suffice - medium for taxiing and fast for showtime, which you switch it to as you take the start line.

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[Jonny Hart]

The Singer DLS-T uses a horizontally mounted brushless electric fan. The fan uses around 80A so you would need to run a high power alternator (as you may drag the voltage so low that you enter a rising current / falling voltage 'death spiral'. 80A at 12V is around 1.3 HP so it seems attractive but you wont just be switching this fan 'ON'. You'll need a control loop for temperature regulation of the fan speed and a brushless fan controller. I would budget £2,500 at least for the parts and a whole load of development.

Given the way the car is used, two speeds with a manual switch would probably suffice - medium for taxiing and fast for showtime, which you switch it to as you take the start line.

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You'd still need a PWM controller. brushless fans do not just 'switch on'.

[MikeB]

Probably better getting weight off the car (and dare I say driver ). What about lightweight body panels, lighter metals etc?

Incidentally, my dad tried taking the fan belt off his Okrasa Beetle back in the early 60s, but on the longer Ulster hills the oil temp rose significantly. But then the Beetle wasn’t dry sumped.

[sfl993t4]

I think the DLS-T electric fan is only used for cooling the cylinders (a bit like the 959 engine fan) as the heads are liquid cooled. Head temp is always the challenge in air-cooled engines.
Big advantage of the flat fan is (relatively) even distribution over the heads (a challenge with the upright fan).

[911hillclimber]

Thank you all for the burst of thoughts!

If I 'time' the engine start, warm-up, time to the pre-start (for a noise test @ 5K rpm) then to the start and off i plan to get the temp gauge (off a 3.2 911) to be 2mm under 'normal'.

By the end of the climb that gauge will show 2mm over the normal (mid range on the gauge) level.

If it looks like a delay to the start area (due to a red flag on the hill say) then I switch the 8" electric fan on that is fitted to the oil rad.

If the delay then gets the engine to normal level i kill the engine. Obviously re=start when i see the red flag come in and the hill is 'Green to go'.

I can't disconnect the engine cooling fan, it is mechanically belt driven.

My original thought was if it were electric then I could have the extra bhp but keep my starting routine.

All the ideas are too complex to be worth it.

As to weight, I'm 13 stone so could save (if i really tried) 20 lb/10 Kg.
The car ready to go is 560 Kg.
The body weighs a mighty 16Kg.
The best weight saving would be another (type) of engine rather than the 911 engine/box that must be nearly 1/2 the car's weight!

I'm not going to fit some bike engine and chain drive, it would be easier to sell the Lola and get a Radical where it is all done.

However, LOTS of people hillclimbing have done this so boring to me.

Looks like keeping it as it is.
ps: I cannot race it like this!

[sfl993t4]

Without too much spending, it might be worth poking a thermocouple down one of the spark plug holes and rigging up a simple temp reader. This might help inform your startup / shutdown routing.
That said just driving it probably the most fun.