2airtime2

that they rob your engine of 30hp.


I ran across some Engine Power episodes on you tube where they dino'd the same engine several times. Each time with a different engine driven fan. They all sucked, literally, your available hp. The stock with clutch, lightweight plastic flex, standard flex...all horrible.


I think the range was around 20-30hp lower for any of the fans vs. no fan. They mentioned even a 30A draw off the alternator (for an added electric fan) only results in about 1 hp robbed from the engine.


I probably would have guessed a 5-10hp drop so I was surprised and will not be putting my factory fan back on.

Danish Shark

It sounds like your fan clutch wasn't working.
When you are driving the temperature drops because of natural air flow through the radiator and the fan clutch makes the fan idle.
In situations where the fan is needed it makes no difference if the power to the fan is mechanical or electrical, it has to come from the engine.
Modern electrical fan designs are probably more efficient, but there is also a loss converting mechanical power to electrical and back to mechanical.

bashcraft

I'm sure they were trying to sell you something. Those Engine Power episodes are nothing but 30 minute long commercials.

Bloodzone

I watched that Engine Power episode. Looked legit to me. They promote oil not fans. I see no reason for them to give false data. But I'm bias. I'm really happy with my electric fans.

terrys6t8roadster

When I first got my 6t8, it had a susposedly 350 hp 327. The exhaust was shot so it got headers with a H-pipe system. Next it received a Holley DP and Elelbrock. Didn't notice much power gain. Had lots of overheating problems due to the fact there was no fan schroud and an aluminum flex fan. Put a Flex-a-lite fan on and noticed a definate increase in power. Also no more overheating. Now both of my vettes have electric fans. T

The Money Pit

Here's my experience. Had a mechanic fan almost go through the hood at 7000 rpms,....went to electric for safety.

The fan is really only needed at low speed to enhance cooling when forward movement is too slow. Like when you're stuck in traffic on a 95 degree day. Once you're moving past maybe 25 mph, the air flowing through the radiator is enough even without a fan, to cool the engine. At 7000 rpms,.....I'll take that extra 30 horsepower,...cause the electric fan is not likely to even be running then.

Frankenvette

I had my vette on the dyno with and without mechanical fan. It was a new fan clutch so should have been working properly.

Dyno operator suggested a few pulls without as he felt mechanical fan was robbing power. This is an old engine to start so there could have been other issues as well.

From dyno printout...

gained

12.6 hp
17.5 ft-lbs of torque

68post

Was this with a thermal or non-thermal clutch ? I don't know how much, if any, difference this would make. Just curious.

Frankenvette

This was about 15-16 years ago, so I do not recall what type of fan clutch. I was new to auto repair so I'm sure I purchased whatever the parts shop owner suggested.

In my case I purchased a used 16" electric fan for around $100.00 a few additional parts plus fabricating my own mount. All in the cost was about $150.00. Would never go back to mechanical fan.

Another benefit is you can work on your engine while it's running and not worry about taking a finger off.

71VetteLover

The engine driven fans consumed 25 to 30 hp at 6000 rpm which would mean they consumed 13 to 15 hp at 3000 rpm or 6 to 7 hp at 1500 rpm. A 60 amp alternator with its field fully energized will consume about 5 to 6 hp when the engine is spinning around 1500 rpm so the actual difference is very small. Electric fans solve several problems while creating new problems. The advantage is electric fans usually aren't being powered at cruising speeds which would increase fuel mileage a little bit and the disadvantage is when they are being powered the engine and alternator are producing their least amount of power. So there are pros and cons.

Now regarding clutch fans have you ever noticed how they ROAR during the first 30 seconds of 1500 rpm engine operation after starting a cold engine and then they suddenly go completely quiet? The ROAR is consuming a lot of horsepower and the quiet is consuming zilch. So their horsepower consumption is dependent on their speed and their temperature. During the Engine Master tests the clutch fan was immediately spun to 6000 rpm in a cold dyno room (they said it was cold and they were all wearing coats that morning). Had they given the fan clutch the time to move its fluid into the center reservoir and THEN spun it to 6000 rpm it would have consumed way less power.

So which is the best for drag racing? The electric fan(s) for sure.

lionelhutz

So you're saying an alternator is only about 20% efficient?

The stock 60A alternator at full output takes under 1.5hp to drive.

A pair of electric fans driven by a properly upgraded alternator takes about 2hp to drive.

427Hotrod

I did some testing on my car years ago. At the time it was making about 615 RWHP. I ran it with and without the fixed stainless steel flex fan using stock pulleys.

Back to back we could "maybe" see 3-5 or so RWHP. It was really almost within the normal run to run variations. Certainly a little better...but no where near what I had heard over the years. In fact, I had already bought an electric dual fan assy. and was looking for a larger alternator to run them. After the testing I took the fans back and have kept my mechanical fan for simplicity and weight savings.

I'm still running it and it's spinning just under 8000 RPM at the finish line in the 1/4 (stock PS pump too!) at 158+ MPH on every pass. I ran a similar fan on my 427 for 20+ years also. No issues. I believe these type flans flatten out pretty well. I've tried it at the track with it removed and could never verify a substantial enough improvement to make it worth the trouble to remove it. Again..I know electric IS better...but I'm not losing any sleep over it. Maybe someday I'll get around to it.




JIM

cv67

x2 either one is fine, personal preference. When it comes to cooling doesnt matter if it eats 2-20 its worth having the right one on there
who cares about a dyno # at that point.

71VetteLover

I had noticed the Engine Masters didn't test a genuine Flex-A-Lite fan but rather tested variants on the Flex-A-Lite design. I would think a fan that starts out being 3" thick and flattens out to 1-1/2" thick would reduce the power loss at high rpm. My '73 Chevy 3/4 ton pickup came from the factory with a Flex-A-Lite style of fan that has 7 really thin stainless steel blades that flatten out. I got a notice from G.M back in 1998; advising me to replace the fan because of numerous reports of them tossing a fan blade. I was really surprised that after 25 YEARS I would get a notice like that so I figured some people probably got hurt.

mobird

Do you have a source for this?

cv67

They do flatten out...had one come apart on my while checking timing.
EM doesnt like those flex a lit plastic ones, I love me. Lightweight not noisy and move plenty of air...we used to turn those over 7200 all night long for years (Saugs Speedway in the 80s) still have one. Cant break those things.

2airtime2

The host, like you, suspected the stock unit with fan clutch would kill the least amount of hp for the same reason you stated. Unfortunately that's really wrong. All 5 (I think) engine mounted fans killed hp ranging from 20 to 30hp and the fan/clutch type was near the top of hp depleting. I (they) addressed your theory on mechanical to electrical back to mechanical cooling, it takes about 1hp from the engine due to additional alternator load.

wendellp601

The math is pretty simple to calculate HP required for a given electrical load.

1 HP equals about 746 watts.

Volts x Amps = Watts

(Keeping whole numbers)

14V x 60A = 840W

840W / 746 (watts per HP from above) = 1.12HP

Divide 1.12HP by whatever factor you think represents the efficiency of the alternator.

mobird

Thanks for sharing that!




Roughly how efficient are our alternators?

2airtime2

Correct. Amsoil, but not fans, so no conflict of interest with these tests.

12.6 hp gain thru a hot radiator. Their test was with a dummy radiator, just for air resistance I guess. I bet their fan clutch would have done better with hot air hitting it.


yep