Fan Clutch

[Jack C.]

Is there a fan clutch available for my application (427/400) that conforms with NCRS judging rules that is constantly engaged in order to generate more air flow? I have tried every avenue to cool the engine compartment down trying to prevent vapor lock with little success.

[Jack H.]

Re: Fan Clutch

Nobody would make such a thing! If you want direct drive between the waterpump and the fan, there are a myraid selection of 'spacers' as installed on GM cars/trucks that didn't employ fan clutch technology. BUT, these aren't going to look like a bona fide fan clutch and you'll take deduction(s) during the judging process.

I guess you could find an original fan clutch and have the shaft either glued or welded to the housing to thwart the clutch from doing its 'thing' and slipping. But, that seems like like a DRASTIC measure!

I know you say you've tried 'everything' to keep the underhood temp down to thwart fuel percolation, but let's examine this... When factory new, these cars had a fan clutch that was functional and did NOT overheat. I'd say you've missed one or more things on your trouble shooting list.

[Jack H.]

Re: Fan Clutch

One more thought... Since the car is a 427/400 configuration, it's reasonably well known that tri-power carb setups don't like today's alcohol doped pump gas. The packing density of the three carbs atop the intake manifold makes BTU dissipation more difficult than a simple, single 4-Bbl setup... Perhaps you're fighting today's pump gas.

Have you tried to fault isolate your problem(s) to the fuel composition? Run the tank almost dry and fill 'er up with fuel that is not alcohol doped (race gas, AV gas). Try to duplicate the 'trigger' conditions that caused you problems and see if the fuel substitution creates a fix.

I HAVE seen tri-power equipped BB cars that couldn't make red line with today's pump gas, but they ran quite decently at lower RPMs without vapor locking and/or percolating...

[Paul J.]

Re: Fan Clutch

Jack C.

As usual, there was a thread on this several days ago, and several suggestions were made which included Jack H's Av and race gas suggestions, although these included blending and some other alternatives. It's only a week or so old but I'll give you the link when I have time to find it.

Paul

[Jack C.]

Re: Fan Clutch

Jack, there's no boil-over but the fuel lines to the carbs get so hot after running for a while, they are almost too hot to touch as well as the air cleaner lid. Fifteen or twenty minute later, the car will re-start.

[John C.]

Re: Fan Clutch

Jack

I have a 68 435hp car in here in Phoenix and have never had any vapor lock or hot start problems with it.

When warmed up my car run at a pretty constant 210 degrees regardless of the outside temperature. It may go to 220 degrees in stop and go traffic but will quickly go back to 210 when moving. What temperature do you have?

It definitely gets very hot under the hood at shutdown, but I can't see how a constantly engaged fan will help you here.

Does your center carb have a idle vent on top? Some do and some don't. I'm no Holley carb expert as to it's actual purpose but I've always thought this should help with vapor lock. My car has it.

John

[Jack C.]

Re: Fan Clutch

John, I have the original carbs and it does have the vent tube.

[Bill C.]

Re: Fan Clutch

Jack,

You can buy an Eaton clutch unit.
Then modify the heat spring up front (controls the lockup) to turn the pin to the left about 20-30 degrees. This will have the clutch unit more engaged much earlier, will come very close to acting like a spacer, except the fan will still spin freely some.

It works --------------

[Jack C.]

Re: Fan Clutch

Thanks Bill, I will give that a try. By the time I get this right, it will be time to put it to sleep for the winter.

[Bill C.]

Re: Fan Clutch

Having the fan engaged 80% of the time through ALL rpm ranges will draw back on HP.

It is a REAL drag on the engine.

Clutch fans will sort of dissengage at high rpms and only spin 10% of the real revolutions.

The Eaton units run around $125+ and if you are not carefull, will ruin the unit. It took me a practice clutch to learn how to twist the spring. Might be worth it to find a bad unit and just practice on it.

Either way - this a a pretty extreme thing to do, specially if there are other ways to cool your fuel delivery down.

[Jack C.]

Re: Fan Clutch

I do have a spare to experiment with. Thanks,

[John C.]

Re: Fan Clutch

John, I have the original carbs and it does have the vent tube.

Jack

I'm not sure we are talking about the same thing so I just want to confirm. Two versions of the center carb were used in 68, list 4055 (early) and list 4055-1 (late). They both have a vent tube on the main body but the 4055-1 added an idle vent on the actual fuel body. It is opened by the throttle linkage any time the throttle is closed. I've always assumed to help with vapor lock.

Many time this will get deleted or even added when a carb is rebuilt and a different fuel bowl is used.

John

[Jack C.]

Re: Fan Clutch

John, I have the early 4055 center carb without the extra vent.

[John C.]

Re: Fan Clutch

Jack

I'd try adding the idle vent on your center carb to see if that helps before going to more drastic measures such as messing with the fan clutch.

I have a center carb fuel bowl with the idle vent in it I can loan you if you want to try it out.

John