Why not use factory clutch fan

[super10brss]

I am in the process of gathering materials and info before I do my 89 chevy truck ls swap, my question is why does everyone switch to electric fans? If the clutch fan on our stock trucks (1989 2wd truck) works fine to keep the engine cool, AND the ls donor truck/suv has a clutch fan to keep them cool (which works fine) why not keep it simple and us the ls clutch fan? Does the geometry get messed up? ie. LS motor not short/long enough for the ls fan to sit "right" in the 1989 factory fan shroud? It's also an extra cost to swap, reliance on battery power, more pull on electrical system, etc, etc.

If there is a "good" reason NOT to use the ls clutch fan, what does everyone use. (I know this is a loaded question because everyone uses something different, but is there a fairly close direct swap XXXX from certain car/truck bolts right up?)

Thanks guys!

 

[jkeaton]

Usually electric fans free up some HP. Not much

 

[OutlawDrifter]

also helps your vehicle warm up faster in the winter time, for that reason alone i'm probably going to put one on my z71. definitely frees up some hp and will bump your mpg's a small amount.

 

[super10brss]

Fair enough... Thanks guys for the responses! Honestly I am going from a well worn in 305 to "modern power". I honestly don't care about the 5 hp that I would gain from the extra expense of electric fans. Which leads to a thought... Comp cams has 3 options for a replacement cam that utilizes the stock valve springs, for the money it would cost to do electric fans I could do a cam swap and gain 50ish hp over stock easy enough. Of course my main goal is to be able to drive the truck in the summer and not have to worry about being able to keep up with traffic running my AC... Maybe I could get the LS swap done and worked out, then cam swap!