I'm mocking up the SBC engine brackets in my lo highboy A****** coupe and wanna know a coupla things from you who have already been there: I am thinking about running a normal fan blade set up with a shroud but need to know what the minimum distance that i should maintain between the front of the blades and the radiator core, and how much clearance around the blade on the shroud, and does the blade need to be fully inside the shroud or about halfway in and halfway out to be most effective? Or should I just scrap that Idea and get an electric one? And if so, which one: a puller (rear mounted pulling air across the core) or a pusher (front mounted pushing air thru the core)? Right now i have about 2 1/2 " between the water pump bolt flange and the radiator core... The blade will be just below the center of the radiator and not down on the bottom like I see a lot of these. Any help is much appreciated...wanna resolve it this weekend and get the danged engine in the car
I set the one on my flathead 7/16 from the radiator since it has no shroud. It will idle all day and never get over 180 with it close and no shroud. With a good shroud I'd think it wouldn't matter how far away it was to pull plenty of air at idle. I see a lot of rods with no shroud and 4 or 5 inches back, they might as well not have a fan.
I have 1/2 to 3/4" from fan blade to radiator. I have 1/2" clearance around the diameter of the blades. The center of the flex blade is centered on the shroud. Be careful on the Pass side and top, I started out with less than 1/2" but when the engine would torque it hit.
I'm one of those guys with 3 inches between the radiator and fan without a shroud. Needs to be closer. I'm gonna make a spacer and a shroud (old license plates) this winter to help keep the ol Flatty cooler. HAMBER Kirk Hannigan had his really close and the bearings went on the fan carrier resulting in a spectacular break down when the fan sliced into the radiator. So don't put it too close.
I have the same type setup on an SBC and it runs 180 consistently. Only on very hot days in stop n go traffic will it creep up to 190. I was worried about it when I first set it up, but haven't had a problem. It's one of those flex fans.
I used to run the big paddle plastic fans for years. They were cheap and would pull a lot of air. Then on my last car I put one on it. I left approx. 3/4 to 1" clearance from the fan to the radiator like usual, but this time when I went through the gears (only reving about 4500) it hit the radiator. So I changed to a big paddle stainless fan. I guess the moral is; don't get it too close and allow for the fan blades to pull forward. You can always put a spacer behind the fan to move it forward, but it is real hard to move it backward.
I have heard far too many horror stories about flex fans to ever run one - not only hitting radiators, but even going through hoods - well THAT would matter ONLY if you actually had a hood!!!. I have also noticed that I can run without a shroud IF I keep the fan to radiator gap on the smaller side. BTW I run a factory steel fan - little flex if any.
Same with me!!! No flex fans! Yeah, horror stories like going through someone's chest too!!! There sure isn't any flex in the "old iron" fan Henry made for my flatty and neither the engine or radiator move around enough to see.
yea...i havent considered a flex fan for the very reason that if a piece of metal flexes...somewhere down the road metal fatigue sets in... and zowie, blades go flyin'...sumthin I dont need....so it sounds like about a 1" gap is about right between the radiator and the front of the STEEL fan blade edge? Then thats how I will set up the engine location then....and center the fan in the shroud but allow room for engine torque movement....is that about right, guys? BTW...nice to get advise from great wrenchers like you guys. Any advise on the electric fans for someone else that might read this???
Well finally something I can give some advice from my 16 years of work at a company that does this very thing. Of course I quit them in April cause I knew to much but that is another story for another thread. LOL. 1st thing is blade to radiator clearance. A general rule of thumb to start is 3/4 to 1" space from fan to radiator. This will allow for flexing and movement of blades 2nd thing is the clearance from blade tip to shroud. If you are not running one and have no problems good. If you are having heat issues then put one on! Clearance from tip to shroud should be 3/4" on average. NOW take into account for motor and******* mount movement along with total chassis flex. If unsure go a little bigger so it doesn't hit! And inspect the tips after running it hard to see of they are rubbing or chaffing. 3rd thing. Flex fans. There are millions of flex fans out there. Really. You would be amazed at the number of flez fans in vehicle s and industrial applications. And yes metal fatuigue is the culprit but you can fatigue anything plastic or steel too! Just keep pushing past the modulus it was intended and it will fail. It is generally (I said generally) not the fan itself that is the issue for bursting (technially term for kablewy). RPM is usually the cause. I run a flex fan and I run my big block up to 8 grand. No problem, but my fan ratio is .73:1 (underdriven) And well within the burst limit. BTW this same fan has been on 4 or 5 cars! Fans are rated by a number of specs but the main one is busrt speed in feet per minute. if you go past that line it will go boom. Using a 24" steel staock balde and reaplacing it with a 24" flex blade is not exactly the best idea. Most times if you look at line to line applications you go up or drop 4-6 inches on different composition blades, See first sentence! Fans are also rated by air movement. This is called CFM Yup cubic feet per minute. That is what is measure at the whole RPM range up to burst or layover of the blade. There are sheets available to the general public called Fan Curves. Use them and pay attention to ratios! Just a primer but eshould get you where you need to go for now. Post if you need more pr PM me. Happy motoring!
Whoops almost forgot. #4 Immersion. Fan immersion inside of the shroud. It really depends on the fan manufacturer and thier performance curves as to what is ideal. A general guideline is 2/3rds in and 1/3 out. Meaning 2/3 of the pitch width inside of the shroud when looking from the side. This is important to get the best performance and also to reduce the chance of stalling and recirculating air inside the shroud hence not cooling. And make sure you are using a*****er fan on the car or have it properly installed so it is pulling air through the cooling package. This is a rare case where if it really*****s it is a good thing! Also don't forget to minimize obstructions in front of the cooling package!
thanks Fuel....so what/how does a person figure out the ratio? and why is it important? does it have to do with speed? also wher are these "Fan Curves" sheets available? On-line? Sounds like you know your stuff. Thanks again. Good food for digesting here, eh?
This is good info? How do you know what CFM you need for your set-up? Is there a formula for square inch of radiator vs CFM for proper cooling?
I have a 1985 Chevy 1/2 ton cargo van with a 4.3 litre engine, which also had the 350 chevy engine option. If you're familiar with the 4.3, it's just a chopped off 350, uses the same mounts, etc. The fan has about a two inch extension on it, and the fan shroud is about four inches longer than normal. The radiator is in the same position for both motors. Just my $.02, but I'd say you could probably get away with the distant fan, provided you had a good long shroud. Ben
Sorry boys was really******** with biz stuff. Taking a quick break on project so here we go. I will answer all in order. Mr. Nvvvrdunn writes: (BTW are you related to Duck Dunn? Jim Dunn, Mike Dunn? Sorry.) "thanks Fuel....so what/how does a person figure out the ratio? You need to find out max speed for the particular fan you want to use. The manufacturer of the fan will gladly give you that info. Then set up your crank to fan ratio accordingly and leave a little fudge factor just for safety sake too will ya! Remeber they make differnt pulley sizes for a reason. This is it. "and why is it important?" So it doens't go boom and fly apart or technically speaking burst. "does it have to do with speed?" Yes it does there is max sustained speed for all fans and if you realize they cycle up and down the rpm range and we all treat them like***** it starts to make some sense to keep it on the safe side. Remember all of the flexing and temperature changes a fan must go though along with the material properties it has a variable life. You treat it nice it will last along time. You treat it bad and it will fail fast. "also wher are these "Fan Curves" sheets available?" Each manufacturer test evey style and size of fan and sets the curve for thier blades. DO NOT****UME every blade for every vendor is the same. A 24" 7 blade from XYZ Corp may not have the same characteristics as a 24" blade from ZZZ Corp. Not all blades are interchangable nor are materials interchangable all of the time. Get the manufacturers recommendations. "On-line?" Most of the good companies either have them on line or in a PDF format they will e-mail you. Or just call them up. Those crazy fan guys just love to talk technical***** to customers. Humor them. (But now you will sound like you know what are talking about or at least looking for) "Sounds like you know your stuff." Easy there big fella don't go that far. As a famous band once played "I know a little" "Thanks again." Your welcome write to the HAMB Answer desk anytime "Good food for digesting here, eh?" Sounds like you need a good meal and are you (Y'ALL) from Canada? Eh? LOL Mr. 4tford writes: "This is good info?" It makes it alot easier to understand why things are like the way they are done. I hope it helps. "How do you know what CFM you need for your set-up?" Your radiator and total cooling package has what is called a total pressure drop and along with top tank or side tank temperature.......Ahh let me slow this down here. If you explain to the fan amnufacturer what you have in detail, height, width, number of rows, and material of each part ie; rad, condensor, charge air cooler...they can get you the proper CFM you need. But a good thing to remember is more CFM good! Too little well you know what happens there. "Is there a formula for square inch of radiator vs CFM for proper cooling?" Ok there grasshopper easy there! You are right on target. Very wise man you are. There are many formulas actually. Mark's Engineering handbook has a good primer and real world examples if you feel the need to break out the ol sldie rule and abacus before we train harder. But you do get an extra bowl of rice tonight for your brilliance. BTW if you are serious about learing some good general rules of materials and systems two books worth haveing are Mark's and Machineries Handbook. You can buy them used or get someones old ones they will make you very smart on lots of things to build a rod or just very good toilet...err library reading material. Ben writes: "I have a 1985 Chevy 1/2 ton cargo van with a 4.3 litre engine, which also had the 350 chevy engine option. If you're familiar with the 4.3, it's just a chopped off 350, uses the same mounts, etc. The fan has about a two inch extension on it, and the fan shroud is about four inches longer than normal. The radiator is in the same position for both motors." "Just my $.02, but I'd say you could probably get away with the distant fan, provided you had a good long shroud." Ben you are the man! Shroud length is really not an issue as long as it is supported properly and doesn't***** in. It could be 20 ft long. The test dyno for fans is called an ASHRAE tunnel or cell. And that has a very long shroud to get straightned air for exact measurements to rate the fan. Long shroud good, no shroud bad. Thank you all for writing in and I really hope you have what you need. If you have anymore questions throw em in and we will see what I can do to help ya. #5 helpful hint. Keep your fan spacers to a minimum as you read earlier too long and the breaings go out in a water pump or worse the shaft will fail. Too much overhung load and the dynamics and harmonics in a fan will tear up the pump. This is the only time in your life someone will tell you being short is good and having a big overhung load is not a good thing. LOL.
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