I'm making nowhere near 800hp, but a mechanical pump and viscous clutch fan have survived since '99 with all my big block combos. Back in the old days I ran a flex fan, dont think I'd ever do that again, but lots still around at the track.

 

I've never really had problems with flex fans except for cutting myself on them while working on an engine. That, and the fear of a blade flying off and hitting me, or doing damage to my fenders/hood was enough for me to quit using them. Those things are sketchy looking.

Interesting thing though, today at work, I was BS'n with the Chief Mechanic out in the shop. He was telling me about how the fins on the impellers of some CAT water pumps will wear down over time. He said they've been doing it for years. At first he had a heck of a problem tracking down why this machinery would keep overheating, as everything checked out fine. But in the end, that was found to be the problem. Then fins themselves, it sounds crazy though, since they don't touch anything but the coolant that flows through. They never leak either.

 

I have never/wouldn't ever run a flex fan in any application!

Besides the fact that they cost/rob HP they are extremely dangerous!

Like Bob, I use the stock 7 blade steel clutch fan!!:yes:

 

I've been running a fixed 7 blade fan on mine for years. Literally the same fan on many different motors for over 25 years! Actually the date stamp on the fan is 1981!

It has spun past 7500 rpm many times using stock overdriven pulleys with no issue. It's been on stock pumps and aluminum ones.

I like the simplicity. I've played with it at the track and on the chassis dyno by taking it on and off and I can tell you I've yet to see anything close to the stuff magazines tell you they use.

I recently set up an external Moroso drive on it where I can quickly switch the setup to use the electric stuff at the track. Not sure if it makes it any faster...but it is nice for between rounds cooldowns.


JIM

 

Been running a GM 7 blade clutch fan for over three years now on a Stewert mechanical pump...never any problems.
However, consider your buddy at work is talking Ford. :wacko:

 

However, consider your buddy at work is talking Ford. :wacko:

Yeah, and a late model Ford at that. Production High perf car parts made in the 80's and 90's just aren't anything impressive IMO. I mean, he must have had the factory stock pump on this late model Mustang he has.:sad: Thanks for all the replies and sharing of experiences so far.:thumbsup:

 

Flex Fan....

Same here, I would never use one. Either the factory clutch fan or electric. Never a Flex Fan for many of the reasons already mentioned especially the safety and the potential carnage.

 

Okay, would you guys recommend a thermal clutch fan, or a non-thermal one? I know how thermal ones work, but does anyone know how the heck "non-thermal" ones do?

 

bg,
I personally have never really liked flex fans, but a lot of people use them and they are safe as long as you buy a good one.

I personally do not see where the HP of the engine has anything to do with the lfe of the fan ???? RPM is RPM, makes no difference if you are making 100 hp or 1000 hp, you are only turning the fan a certain rpm.

Just my opinion,

 

bg,

I personally do not see where the HP of the engine has anything to do with the lfe of the fan ???? RPM is RPM, makes no difference if you are making 100 hp or 1000 hp, you are only turning the fan a certain rpm.

Just my opinion,

Yes, that's what I always thought Bill. That's why it really surprised me to hear what this guy was telling me. I have a Flex-a-lite flexfan that I had planned on installing, which has a label on it that states that it's maximum RPM is 8,000 and my engine will never be reved past 6,500 RPM.

 

I've run the generic parts store non-thermal clutch fan combo for years with no issues. Billy, the non-thermal clutch fan is a viscous fluid coupler. When I was a teenager a local kid got a flex fan blade shot through his neck while he was standing next to a revving engine. I know that it was a cheap flex fan - but no matter, I swore to never use one.

Thomas

 

I guess I buck trends.

The Nova has had the same FlexAlite flex fan since 97. Along with an Edelbrock water pump. Stock pulleys btw.
I'm sure it costs some performance.? (Fan + pump)

But I drive the dang car, to the track, and it runs cool.
Tried an electric fan setup once.....car ran too hot, and no diff in perf. None!

But maybe a stock clutch fan would be a good deal....I haven't proved that on my car.

Many spend $350+ on a fancy electric water pump on street driven cars, and they work great. Then you also need a GOOD electric fan setup....which draws a bunch of amps from the alt....I don't see the HP savings there.

My car always runs cooler at the end of a 1/4 mile run than it does at the start.

In fact, when it's below 80 outside, I have to warm it up before a run!

Diff strokes I guess.

Ron

 

The only reason I run electric now is to be able to cool the car off between rounds. I am sure this is the same reason many others do too.

Once you get into the 4 th round, round robin starts, you need to be able to control the cooling especially in the hot summer.

 

What likely happened is the blade(s) came off his fan, destroying the belt and everything else with it.

If you're going to use a flex fan, use a good one, like a Derale or similar - not a bad idea to keep an eye on how well it stays riveted on, either. They are great at low-speed cooling, but are pretty noisy as they move all that air. If your cooling system is all working the way it should, a stock setup should work just fine.

 

GM thermal fan clutch, 7 blade factory GM fan, GM shroud, and a Stewart aluminum water pump on my 540, all driven with a single V-belt and GM pullies.

It runs 170-185 ALL the time, no matter how hot it is outside, and it's been fine at 7000+ rpms.

I've run the same setup on several street racer cars, some of which were buzzed to nearly 8000 with no issues at all.


Randy

 

I agree you need a good one. And as mentioned....I keep an eye on the rivets.

Make sure you are figuring fan speed. My water pump pulley is overdriven with the stock pulleys..that means fan is turning more than engine RPM.

Years ago I played on the chassis dyno...I pulled fan off and made some back to back runs. At the time it was the first version of the 540 and it was making 615 RWHP. The difference between the runs could have been run to run variation because I never saw more than 3-6 RWHP difference either way. Sometimes it was less power without the fan...sometimes it was more. I had bought an electric fan because I just knew it was going to be big power. I took the fan back. I haven't really done any back to back testing with electric and regular pumps....but the engine dyno guys I know say they never see anything close to what the ads claim.

Electric pumps are great on the street in low rpm cruising because they move just as much water as they do at high speed.

But as mentioned all of this takes a big alternator. I'll stick with simplicity...and if I was going to change anything, I'd use a big stock fan with a thermal clutch.


JIM

 

If coolant gets past the front water pump seal the pump will probably freeze up. If that happens the results are real bad. The fan can then no longer pull the air through to the engine so it usually breaks the shaft and the fan then goes forward into the radiator. That is probably what happened to your friend's Ford. The small "weep" hole in the front of the water pump is to alert you that you have a defective seal. When water comes out of this hole stop driving the car and change the pump immediately. I like the newer electric fans if you first find a good way to mount them and then get big enough ones to keep your motor cool, which usually takes two, mounted side by side.

 

Fan RPM can be quite different from crank RPM! Pulley combinations can underdrive, 1 to 1, or overdrive the fan. Look at the march stuff for a SBC. You can order pulley combinations to achieve three different levels.
They sent me the overdrive system first and when I had the car at the track the it sounded like a turbo prop spooling up!

 

Aren't the blades on a clutch fan riveted on as well? I spin my motor to well over 7000, i have used a flex fan for many years without issue, i've also used a clutch and a stock 5 blade fixed fan...

the only issue i had is my alternator fan blades started to straighten out and cracked!! -anyone hear of that one? i went to o/size pulley on it after that!

a

 

the only issue i had is my alternator fan blades started to straighten out and cracked!! -anyone hear of that one? i went to o/size pulley on it after that!

My first 327 that I had back in 1970 used to do that all the time if I missed a gear when powershifting above 7000. I even slung a few blades out through the hood once! I finally put on an oversize pulley and the problem stopped.

Randy

 

GM clutch fan ( mines the original 66 5 blade ) and as others have said a good water pump ......Stewart !! the stage 3 has a larger impeller shaft 5/8"

I have heard of Mopar water pumps blowing up from exteded rpm taking out the fan etc ......go quality pump and make sure the water pump pulley is the correct size relative to crank pulley for the cooling and rpm needs of your motor FWIW

 

You guys have given me a ton of fantastic info as well as experiences that you've all had. Thanks alot! BTW, sometimes I wonder why Corvette water pumps have 3/4" shafts, while Chevelles come with only 5/8" shafts.