I was doing some research on alternators for another vehicle project. Using some of the advanced research search engines ... Google is useless for this particular research, all you get are endless links to OEM replacement alternators for sale, a few dozen to some guy doing a wind generating project, and 10,000 links to Chinese manufacturers offering to build anything you want, as long as you buy 1000 of 'em ... I came across this page.

The guy had a built engine on an engine dyno, and a week to play around.

He tested engine mounted fans of the usual types with a simulated radiator and with the OEM shrouds.

1st: Big Block Chevy OEM direct mount fan
2nd: same fan, with thermo-clutch
3rd: A popular junkyard fan for these motors from a 6cyl Plymouth Volare
4th: The Flex Fan

His test regimen represented, I thought, a good understanding of the issues related to cooling requirements, power losses and acceleration. I especially liked that he looked at acceleration because that is an issue that doesn't show up on straight peak power "brag numbers" when dyno testing but does show up in the real world when drag or track racing, or just driving on the street.

The best fan for cooling was the direct mount OEM fan, but it ate 40.8 HP @ 4500 RPM. It was pretty easy on the motor taking 8% longer to spool to peak RPM compared to the motor on the stand with no fan test assembly attached.

Next best for cooling was the same fan with the thermo clutch, which ate 35.6 HP @ 4500 RPM but torque loaded the engine to the point where it took 13% longer to spin to redline when hot (ie engaged). When free-spinning (cool) it still managed about 2/3rds CFM, but only ate 19.3 HP. However it still loaded the motor enough to cause 11% longer spin to redline.

The Plymouth Volare fan fared well; CFM was decent, HP loss at 4500 RPM was 31.5, and the motor spun quickly to redline, only 7% slower than no fan test fixture at all.

The FlexFan had the lowest CFM, only ate 20.2 HP @ 4500 RPM (2nd to the thermo-clutch in cool state) and was 5% slower to redline.

We could stop there; that's all interesting stuff for a gearhead like myself.

But wait, there's more.

He then did the same engine dyno test with just an alternator attached.

He loaded the alternator to put out a constant 65A load @ 13.65 VDC. If you see where I'm going here, that's in the ballpark for what load you might get from a running truck or car, some accessories and lighting engaged, with a decent electric fan attached and running in place of the above.

Total HP loss ... 1.28 HP @ 4500 RPM (4 runs; 1.29~1.26).

This motor was a built GM 350 and he had done a series of 10 runs that were consistent within 0.5% of the average, 358.6HP and 385 ft-lbs of torque. Would probably be maybe 270 Rear Wheel HP installed with typical truck driveline losses.

But wait ... there's more.

He did some tests with motor oil. Not much; but the results are interesting.

He ran the motor on the dyno once more, to get another baseline after the break-in runs, power runs, fan test runs, and alternator runs, because all this run time from build-up is improving ring sealing (we hope). Peak HP 360.4. So I guess his rings were sealing up nicely.

Switched the oil (probably straight 30wt, he didn't say) to Valvoline Full Synthetic 10W-30 and got 363.5 HP.

But, he noticed another thing during the Syn test. For the whole week, he's got temp data from the motor runs. Water temperature (external cooling system in the dyno room) was consistent. But the Syn Oil temp was 9 degrees F cooler than the original oil.

Read it all here, if you need the details, but pretty much everything is already noted above. I don't like to say something like "cool results!!!" and then just leave a link because I've been on these Interwebs a long time and links you saved because they had some important info you thought you needed WILL just die, right when you look for them again. So, just in case that happens it's mostly all above.

http://carnut.com/ramblin/dyno.html

So: Syn might be better (I would have liked some 10W-30 dyno oil in there too), and Electric Fan is definitely the way to go.

 

Astute observers might notice that his alternator test was based on the original 358.6 HP baseline, and right after the alt test he was making 360.4.

So, you could make a case that the HP loss for the alternator was 1.4 HP higher than reported ... around 2.7 HP. Still nothing compared to the engine-driven fans, though.

 

Thanks for the information...very interesting for me since I have a TCP setup in the works.

 

I read the results myself from the link, and while they were an interesting read, the alternator test did not mention the use of an electric fan.
While 65 amps would be plenty for a cabureted street rod with an HEI ignition, standard lighting, and small stereo, MPI vehicles draw more than 65 amps after startup to run the various onboard systems. If they didn't we wouldn't need 120 - 160 amp alternators.

While I'd be willing to believe that an electric fan setup (dual fans) likely draws less alternator HP than a oem clutch fan..I'd want to see the test. If you can find such a test, it would have more merit.

 

Simple math tells you it takes about .5hp to drive a 30a electric fan. Add in efficiency losses and call it 2hp, big deal.

I've always said when my OEM clutch fan locked up, the truck felt like a total turd, 20-30hp easy.

 

I noticed a difference going from a clutch fan to E-fan as well (same-ish setup as Hahns, ~30 amps), mostly off idle, but all through the rpm range as well.

 

The only time my fans even come on is when I'm just sitting still idling for a long time. The only time there is parasitic drag via alternator from the fan is when the fans are actually running, or perhaps within a moment or so of them turning off as the battery gets topped up. ie most of the time my efans presents no load at all to the engine. It's a great tweak imo.

 

^^^ I need to get a better controller so that mine stops running constantly.

 

the only big thing i noticed was my truck was almost silent. you can barely tell it is running some days. i have even pulled up behind people and scared the crap out of them. before you could hear the fan moving air. another benefit of them is i could see them allowing my truck to reach operating temperature quicker which is a good thing since winter is getting closer.

 

I put an efan in my Dakota....immediate gratification.