Electric fan for cooling? Options

[teamgravy]

We are building a track car for endurance racing in Lemons/Chump Car series from a 74 914-4 1.8/carb converted. Rules state we have to spend no more than $500 on the car minus the safety equipment (seat, cage, tires, wheels, brakes, etc..)

I am thinking of leaving off the 914 cooling system and much of the engine tins and running a electric fan to cool the motor. The fans are cheap $70 for 2100 CFM fan and I can also use some big ducting to cool motor at speed. Elec is free (no night racing) right and no HP drain. Just loosing the 50lbs of fan/ducting on the front of the motor seems worth it.

I would build a shroud and use some of the existing tins push air across the jugs and heads. I would relocate the alternator above the oil fill/breather and run it off the small AC pulley that was behind the fan. Would love to buy a DTM or Fat 911 conversion kit but not allowed in budget.

I was wondering what the peanut gallery thinks of this.

Is this going to give me cooling issues?
Will ALT function from smaller pulley?

Thanks!

[ArtechnikA]

...The fans are cheap $70 for 2100 CFM fan and I can also use some big ducting to cool motor at speed.

...Will ALT function from smaller pulley?

The Little Spec Book rates the stock coaxial fan at 800 liters/sec at 4600 rpm which is 1695 cubic_feet_per_minute - so you're in the ballpark on airflow.

But - how many amps does it take to make 2100 cfm, and Watts (pardon the pun...) that in HP ?

Keeping in mind that there are coupling loses in the alternator drive the coaxial fan doesn't have. The alternator will run with any size pulley, and it's a common racer's trick to run them with small(er) pulleys on high-revving engines. But it's gotta rev fast enough to make the power you need (plus stuff like ignition, fuel pump, cool suits? Helmet blowers? ...).

You may be able to pick up some airflow efficiency with an external oil cooler, at some cost in drag. And weight, due to the hoses and fittings, although the tradeoff is you can move the weight to where it helps you. And the downside is more risk of damage due to contact or debris.

The upside of the coaxial fan is it only draws power (roughly) proportional to your need for cooling.

[ChrisFoley]

The Little Spec Book rates the stock coaxial fan at 800 liters/sec at 4600 rpm which is 1695 cubic_feet_per_minute - so you're in the ballpark on airflow.

That would be good if CFM was the important measure of a fan's ability to push air through the cooling fins of the engine.
Electric fans designed for moving air volume typically don't produce much head pressure, and stall easily when backpressure increases.

[ArtechnikA]

Electric fans designed for moving air volume typically don't produce much head pressure, and stall easily when backpressure increases.

Yup - I agree.
However, I believe the engine-mounted coaxial fan also stalls at high revs - not coincidentally when backpressure reaches 'some point.'

It'd take a dyno setup or more CFD than I have access to in order to measure or model what 'some point' is. But I believe this is one of the several reasons 'some number' of vanes are removed from the fan for high-rev operation. And I'd expect you'd consider that number more than a little proprietary, so I won't ask ;-)

But I do know that 935's completely removed all the upper cylinder fins and improved cooling as a result...