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Any way to bump up my RPMs when fan comes on?

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Bill.........unless you have an overheating problem and need the extra CFMs sucking small animals and children into your grill why not swap it out for a low profile one that pulls only 4 amps? I know it gets hot and humid in the Bayou but we get plenty of 90 degree and 90% humidity days up here and I've never had my needle move to 1/2 mark on the temp gauge. Even the 16" medium profile fans draw 1/2 the amps that you are. You can always sell the high performance one on eBay. :driving:
 
TR3driver said:
Oh BTW, I agree with your Spal rep; the fan will draw considerably more than it's rated current for several seconds after power is applied. But the alternator need not supply this extra current, in a well designed system the battery should have no trouble picking up the difference. This is basically what happens at idle, with the stock alternator and the headlights on. Once you leave the stoplight, the alternator recharges the power taken out of the battery.
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Bigger battery? I already have an Optima Gel, with plenty of cranking amps. Maybe my battery is getting weak.
 
Bill,

I have the same Spal fan as you. We both have the Spal relay kit wired in the same way. The only difference between cars is that I have the Bosch 57 amp Fiesta alternator and the Masters headlamp wiring/relay package. But mine still won't dip more than 50-100 rpms even with the PL700 headlamps turned on and the fan turned on with the manual switch.

I wonder if you have a problem with that particular fan unit?

I would check the alternator output at idle, under no load, with headlamps on, then with H/L off and fan on.
 
TR6BILL said:
Maybe my battery is getting weak.
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Well, since we can't seem to nail this down; try measuring voltage directly across the battery with the fan on at idle. If you see something in the realm of 12.6 to 14.5 volts; the battery is not the problem, nor is low output from the alternator.
 
I just realized that there might be another difference. I have a new Optima battery. I don't know how old your battery is.
 
A little off topic but what model GM alternate are you using Bill. Also what model Bosch are people using. Do they require alot of modification to install. I will now return you to your originally scheduled thread. Thanks
 
If the battery checks out okay, I thought Randall's suggestion for a smaller pulley on the alternator (to speed it up) would be good to try.
 
As I tried to get across a "Delta" design alternator produces more output at lower engine speeds than the more common "wye" design.

That is why emergency response vehicles have them installed. The vehicle can idle for extended periods of time with large electrical loads being drawn.

https://www.autoshop101.com/forms/alt_bwoh.pdf

Might help explain.

I remember Brosky saying that he installed one. I truly believe this will help your problem considerably.
 
Hmmmmm.....Good question Bob. Let me clarify that and I apologize in advance if I was giving incorrect information. I thought that Art said mine was the "high performance" version. I'll dig out the invoice later today and post back.

The boss is reminding me it's time to go tile shopping.......oh joy......and then to the home show. The fun never stops around here.
 
746 watts= 1 horse power. So at steady state, your fan is using .422 HP ((14.3v*22amps)/746). I know it does not sound like much, but at idle, at best your engine is generating maybe 5hp. With the fan running, that is an 8% increase in load.

The real killer is when the fan first starts. When the switch closes the fan circuit looks like a dead short, which will drop the battery voltage, which in turn cause the alternator to potentially go to maximum output and suck up to 1.4 hp from your engine. 1.4hp represents a 27% increase in demand for power during that short start up period. Hence the stall.

A large, or even a fresh battery will cushion the start up surge effect because it can provide more amperage without a significant drop in voltage.

Time for more coffee.
 
You forgot to factor in the efficiency of the alternator & it's drive, Ray. If it's only 50% overall, that would double your hp numbers.
 
So, would bumping up to a higher AMP alternator, perhaps with the Delta config, help. Or would there be a down side. Like smoke. I will get a new Optima (mine is 4 years old, perhaps is on its down slide) rated at 100 cca. I would like to stay with the Delco-style alternator because it is easy to fit. Might have to go to an online store to find a better alternator.
 
You are so correct. :yesnod: I was just trying to be nice to Bill.
 
TR6BILL said:
So, would bumping up to a higher AMP alternator, perhaps with the Delta config, help.
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My answer remains "I don't think so".

But I just thought of an even easier test to make: Disconnect or disable the alternator entirely, then start the engine and see what happens when the fan comes on. If the rpm still drops, the problem is lack of electrical power and a bigger alternator might help.

If the rpm doesn't drop, then you know the problem is the power being taken by the alternator, and a bigger alternator will not help.
 
Brosky said:
Here is my Bosch story. Very easy swap, for the proper year, See web page for details: https://www.74tr6.com/alternator.htm
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One point not mentioned on Paul's site : Not all 78-80 Ford Fiestas had Bosch alternators. Most of them had Motorcraft alternators, which mount differently and are a much harder swap. The Bosch unit was apparently only original on cars with A/C or heavy duty electrical.

Someone long ago claimed the part number was D8RZ-10346-AX; but that appears to be a Ford part number rather than Bosch.
 
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