The GM four bladed fan is hard to beat. The four bladed fan has a large blade surface with a deep pitch and pulls a lot of air through the radiator. Combine the four blade with an air dam (a channeling box in front of the radiator) with a quality fan shroud (a box on the back side of the radiator creating a fan tunnel) for best results. You also may need to install a good quality water pump -- Stewart Stage 3 -- and a set of 30% reduction pulleys. Finally, take a hard look at your radiator and the fluids. Inspect all of the fins on your radiator and make sure none are crushed. Wash the fins of the radiator from both sides. Then inspect the inside of your radiator. We all run water or at least we are supposed to run water. The only legal additives at least out here are water supplements such as royal purple's Purple Ice/Water Wetter. Make sure you know what fluids are in your radiator.
In our testing on our chassis dyno, we found that the GM 4 blade fan with zero slippage will cost you about 20hp at the rear tires. Simply switching to the All-Star 18" 4 blade with 4 degree's less pitch will gain you back 10hp at the rear tires. Taking it one step further and cutting two blades off of the same All-Star fan will gain you an additional 5hp back to the rear tires. The overall result with the 2 blade 18" fan was a total loss of 5hp at the rear tires vs. no fan at all. I've run this two blade on my house car now for a season and a half, with zero cooling issues. Obviously we have a fabricated fan shroud. I personally believe the two blade cools better.
I've only experimented with OEM fans and tried eight blade, seven blade, six blade, five blade, and four bladed fans. I learned through trial and error that more blades does not mean more air flow. In fact, it's just the opposite and more fan blades creates the helicopter effect -- the blades spin so quickly that they act like a wall (a wing in aeronautics). It never dawned on me to cut two more blades off of my fan. Thank you, Mr. Hendren, for the tip. I've got to run 1" lift motor mounts so my fuel pump doesn't sit on the frame cross member. I can only run a 14" fan or I have major clearance issues. Have you dyno-ed the smaller diameter fans? How critical is maintaining the balance of the fan as you cut the extra blades off, and what's the most expeditious way for a garage mechanic w/o access to a fabrication shop to ensure the fan is still round?
use your water pump to insure that your fan is straight and even-----without a belt on the pump you can use the pump to check the runout of your fan-----simply clamp something to the header or other fixed surface as a pointer.
If the fan is NOT running true---un-bolt it and turn it 180 degrees and try again--this will tell you if its the pump or the fan that is not true (or both)
Balance is critical IMO and just because the fan is true does not mean it is in balance.
a simple lawn mower blade balancer works great and can be purchased at any hardware store for under 20 bucks
a "blade" balancer is a T-Pee of alignment steps and the 5/8 hole in your fan will find a perfect home on one of the steps-----then the T-Pee is placed onto a vertical peg to view the static balance
perform this on a flat and level surface and you can see and measure the actual static balance of your fan blade
keep in mind that once in motion any---static out of balance will be multiplied into a dynamic weight
get it as close as you can
good luck this takes patience
Lt.Stryker & ncracer1st - We've tested the 15" four blade on the dyno and raced with it successfully. Basically it draws the same HP from the rear tires as the 18" two blade. The drawback to the 15" that I see is that your fan shroud has to be built like no other (i.e. it needs to be perfect!) in order to cool properly in a race. The 18" two blade doesn't seam to require a mechanical engineer to build a shroud. lol
Brad is right on the fan balance. But we are lazy, and simply cut two blades off of the All-Star 30105 18" blade. We make the cut right where the blades cross over each other (reference the pic I've attached). Knock on wood, we've had no balance issues doing it this way so far.
none of what I am going to say has been specifically tested by us with data but has been relayed to us through our associates and I would not post anything that I believe to be incorrect
no matter what chassis--- a 1/4 inch could make a difference so we recommend checking and adjusting per your set-up
proper fan distance from the radiator WITHOUT a fan shroud is 1 1/4 inches
fan distance WITH a fan shroud is irrelevant (within reason) but the fan should be approximately 50% inside the shroud and 50% outside the shroud
we have used both of theories and found them to be accurate but have no documentation to back it up
Brad
Last edited by brad hibbard; 02-13-2014 at 06:50 AM.
Hendren Racing Engines is now producing the 2-blade fan discussed in Steve Hendren's post. They have given us the exclusive right to sell them online. You can see them here: http://store.crateinsider.com/2-blad...acing-engines/
Senior Member
cooling fan
Reply With Quote
Posting Permissions
Bookmarks