Anyone Feel Like Running a Mechanical Fan?

[olds307 and 403]

That fan does move lots of air!

The SBO 403 is a tough engine to cool as most classic Olds guys know. With the old stock mechanical fan, I would observe 'temperature stacking' while in traffic and during other situations. With the four blade fan shown above, the engine can actually be kept within my desired temperature range.

I know that as far as performance goes, the electric fans are the way to go. My car is all old school tech and just utilized as a weekend cruiser that doesn't see the track. Not a performance machine as far as today's technology and for this reason, the mechanical fan is just fine.

Didn't your car run 13's, Frank? I think my 4 blade will be kept as a just in case fan. If I sell the 88 it will get one of the power robbing plastic fans. As pointed out on low rpm motors like the 260 in have, I noticed difference going to electric. On a car running 5,6 or even 7K+ there are quality header and exhaust sized gains but much cheaper and easier to do.

 

[foxtrot]

Didn't your car run 13's, Frank? I think my 4 blade will be kept as a just in case fan. If I sell the 88 it will get one of the power robbing plastic fans. As pointed out on low rpm motors like the 260 in have, I noticed difference going to electric. On a car running 5,6 or even 7K+ there are quality header and exhaust sized gains but much cheaper and easier to do.

Hi Christian, It's only seen the track a few times and the was a while ago but it did see high 13's on street tires. This was also with the old mechanical clutch fan..

 

[foxtrot]

I still can't get my mind wrapped around how an electric fan would use less horsepower over time. Let's say that both a mechanical and an electric fan had the same maximum CFM specification. I know that the electric fan could have a constant RPM unless it's variable rate. I also know that the mechanical fan's CFM rating will vary with RPM. Both fans could utilize similar amounts of kinetic energy to produce the same maximum CFM of air flow. The mechanical fan will get it's kinetic energy directly from the engine, while the electric fan will get it's kinetic energy indirectly from the engine thru the alternator. With this said, help me understand how one solution yields more rear wheel horsepower than the other. I do understand that the electric fan will cycle off/on and the mechanical fan has a constant drag.

 

[UNGN]

Wondering...at high engine speeds could overheating be caused by the coolant flowing through the rad too fast to draw the heat out?

Maybe, but most modern mechanical fans are designed to go flat by 4000 RPM. If they don't go flat they would eat even more HP.

We put on a deeper core support airdam and electric fan and the overheating completely disappeared, with no changes to the radiator, water pump, coolant or thermostat, and we actually can turn the motor faster now because it is only 190-200 degrees, now.

After the electric fans were added, we were also able to block off the upper grills for better aero, which completely eliminated front end lift at speed.

 

[foxtrot]

Maybe, but most modern mechanical fans are designed to go flat by 4000 RPM. If they don't go flat they would eat even more HP.

We put on a deeper core support airdam and electric fan and the overheating completely disappeared, with no changes to the radiator, water pump, coolant or thermostat, and we actually can turn the motor faster now because it is only 190-200 degrees, now.

After the electric fans were added, we were also able to block off the upper grills for better aero, which completely eliminated front end lift at speed.

You had mentioned that you now run a 'taller' gear and I'm thinking that this also helps the engine run cooler by operating in a lower RPM range.

 

[UNGN]

I still can't get my mind wrapped around how an electric fan would use less horsepower over time. Let's say that both a mechanical and an electric fan had the same maximum CFM specification. I know that the electric fan could have a constant RPM unless it's variable rate. I also know that the mechanical fan's CFM rating will vary with RPM. Both fans could utilize similar amounts of kinetic energy to produce the same maximum CFM of air flow. The mechanical fan will get it's kinetic energy directly from the engine, while the electric fan will get it's kinetic energy indirectly from the engine thru the alternator. With this said, help me understand how one solution yields more rear wheel horsepower than the other. I do understand that the electric fan will cycle off/on and the mechanical fan has a constant drag.

An electric fan spins slower and because it doesn't have to spin to 6,000 RPM, an electric fan can be built lighter. HP required to spin up something isn't linear, but roughly goes up with the square of the RPM increase and weight is in that equation so a heavier fan takes much more HP to spin up than a light one.

An electric fan probably takes more power than a mechanical fan at idle, but the load doesn't go up with the square of engine RPM.

 

[UNGN]

You had mentioned that you now run a 'taller' gear and I'm thinking that this also helps the engine run cooler by operating in a lower RPM range.

We actually switched back to a 3.25 gear a few years ago. We also put in lighter/stiffer valve springs, pocket ported the heads and a 6,200 chip into the MSD (up from 5,700). I rev it way higher now than when it was overheating with the mechanical fan.

Also note that we used a straight mechanical flex fan AND then switched to a clutching mechanical fan that was larger but was supposed to "take less HP". It destroyed itself after one race.

That was when we made the call to Ramchargers to buy an Interpid/300M fan. Today there are at least 5 of these in every junkyard for about $40.

 

[foxtrot]

An electric fan spins slower and because it doesn't have to spin to 6,000 RPM, an electric fan can be built lighter. HP required to spin up something isn't linear, but roughly goes up with the square of the RPM increase and weight is in that equation so a heavier fan takes much more HP to spin up than a light one.

An electric fan probably takes more power than a mechanical fan at idle, but the load doesn't go up with the square of engine RPM.

Thanks.

From a physics point of view there are many variables comparing the two solutions. It would be a fun and interesting product to gather all of these variables and model both.

 

[foxtrot]

Thanks.

From a physics point of view there are many variables comparing the two solutions. It would be a fun and interesting product to gather all of these variables and model both.

Project not product.

 

[lilbowtie]

Got a lot of people thinking on this thread - should throw electric water pump in there too!