Electric Fans For Your Street Corvair?

You must be a newbie!  The short answer is: "don't bother."   Here's a typical conversation on this topic with someone trying to improve on Chevrolet's simple and efficient belt-drive design:

In a message dated 7/6/01 7:57:04 PM Eastern Daylight Time, warren2@bellsouth.net writes:

Does anyone know how to set up an electric cooling fan on a vair for street use?

thanks!


Date: Friday, July 06, 2001 6:00 PM
Subject: Re: [fastvair] electric cooling fan

You can't. The power requirements to spin a fan with enough oomph to properly cool the engine WAY exceed the power available in most cars electrical system.

John


02:50 AM 7/7/2001 -0700:

what? you better check how many amps are being pulled from a new fans ! http://www.jcwhitney.com.  heres a 16 in fan 1835 cfm 11.0 amps or puller 1949 cfm 10.7 amps.  my truck has two fans a 16 and a 14 with 4 off road lights a radio a heater fan window washer running with a 80 amp alt.  i could not find my copy of how to hot rod a corvair but i think 1835 cfm is more than a stock fans has!

michael


Date: Sat, 07 Jul 2001 10:40:20 -0400
Reply-To: fastvair@yahoogroups.com
Subject: Re: [fastvair] electric cooling fan

Michael, here's why it isn't practical to do (note that I didn't say "can't be done."):

A) Yes we need about 1800 CFM of air flow over the engine to keep it adequately cool.

B) Yes there are electric cooling fans that produce 1800 CFM airflow. But:

1) these fans are optimized for moving air with a minimal restriction in the output path--radiators are optimized for easy flow of a lot of air (large cross sectional area and orifice area) at minimal pressure head (typically less than two inches of water)--which is why electric fans on water pumping cars don't run unless you're sitting still or have the a/c on--the slight amount of pressure head generated by the car's forward motion, even at 20 MPH, is enough to keep the engine cool

2) The Corvair engine requires a pressure head of about 12 inches of water to force 1800 CFM of air over the fins in the engine. This is an engineering tradeoff between weight and packaging requirements for the engine and volume and pressure requirements for cooling, and is DESIGNED IN. The only way around it is to remove heat some other way, by using ceramic coating, active oil cooling, and larger oil coolers. If you're up to casting new cylinder heads, you could put more fin area on them...

3) result of 1) and 2) above: it takes a lot more power to push 1800 CFM over a Corvair engine than it does to push 1800 CFM over a big radiator because you have to COMPRESS the air to make it go over the Corvair engine. How much power?

C) Right at 14 HP at 4800 RPM, according to GM test reports. If you want to turn the engine faster, you'll need more power yet, because the fan gets increasingly inefficient at higher blade tip speeds. If you want to keep the engine RPM below 4000, you're OK with a mere 8 HP fan motor.

D) Let's go with the "optimistic" 8 HP figure. According to my quick conversion, that's about six KW of power. 6000 watts at 14 volts (line voltage on your car) works out to about 430 amps draw. Mind you this assumes 100% conversion efficiency. In practice, you're lucky to get 70%, so that actual power draw from the engine will go up to more than 10 HP.

E) So now we need a 500 amp continuous-output alternator for our corvair (presuming you're going to run any other electrical load, you need more than the 430 amp minimum). Such things do exist--they're found on heavy trucks. They weigh about 60 lbs and need triple-pulley belt drive. And they're large: typically over a foot long and more than 10" in diameter. And it has to be 100% reliable, because that 430 amp load would suck a car battery dry in about two minutes of driving with a dead alternator...

F) Having created the power, we now need to pipe it to the motor on top of the fan: Big jumper cable wire should do the trick...

G) Now the important part: The fan motor must be 100.0% reliable and capable of making 8.0 HP continuous. All the motors I've ever seen that meet these specifications weigh more than 75 pounds, are more than a foot across and 18" long, and typically run on 440 V three-phase AC. But we don't have 440 V three-phase handy in the car so...

1) we either design a DC-three phase AC inverter that can handle 6 KW, heat-sink it properly (it'll need a LOT of cooling), and hope that the fan power leads never go to ground, or

2) we design a 100% duty-cycle 14 VDC motor that produces eight HP and will fit in the Corvair engine bay. I've never seen one. Neither have you. And if one exists somewhere, it weighs at least 50 lbs.

Conclusion: You have spent a lot of money and a lot of time to add over 120 lbs to your car and suck up more power than the stock cooling fan because of lower conversion efficiency.

Still want an electric fan?


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