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Author Topic:   Does the 4 blade fan pull significantly more air?
FirstLight7
Dirt Full Roller

Total posts: 30
posted April 11, 2003 10:38 AM
Anyone know if the Afco 17.5" 4 blade fan pulls significantly more air than the 16" stock 6-7 blade fans?

I may try a 4 blade tommorrow. Extremely mild 350 (limited mod on gas)- 245 temp quickly cools to 200 when spraying down the radiator with a fire extinguisher. Max size radiator 19x22, there are other things that I can do but (other than timing) the new fan seems the quickest.

Thanks in advance for your reply !

dirtbuster
Dirt Freak

Total posts: 353
posted April 11, 2003 10:49 AM
I would make sure you are not running lean on jetting first. I know a guy who fought heating problems for weeks changing fans, and radiators etc... then found out he was really lean. You might also try adding a shroud if you dont already have one. If you dont have a shroud mount the fan about 1/2" away from your radiator so the fan will pull air through the radiator not around it.

In my opinion the 4 blade will pull more air. Here is why. The more blades you put on it the closer it becomes to a solid disk. If you stick a solid 18 inch metal disk out there it wont pull any air. At high rpms the 6 or 7 blade fans are turning so fast and the blades are spaced so close together that they act like a solid disc and are not able to grab any air. Look at it this way.... you dont see too many 6 or 7 bladed airplane propellers, usually 2-4 thats it.

RC Racing
Dirt Maniac

Total posts: 144
posted April 11, 2003 01:13 PM
I've also heard it's a good idea to set the radiator at a slight angle. This forces more air onto the cooling fins, as opposed to passing quickly (effortessly?) over them.

Seems logical, I just wonder if there's any truth to it. Any comments?

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ohiodirt
Dirt Full Roller

Total posts: 46
posted April 11, 2003 07:15 PM
rc,
i'm no expert, but i'm not too sure about the angle thing. i would think alot more turbulence would be caused.

superdave
Dirt Forum Racer

Total posts: 89
posted April 11, 2003 07:26 PM
Turbulance is correct. But air that passes too quickly through the radiator doesn't pull out much heat.

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Superdave
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rico 08
Dirt Freak

Total posts: 372
posted April 11, 2003 09:17 PM
DIRTBUSTER nailed it,the more blades the more they block the air at higher rpm.The 4-bladed fans are usually found on the diesel's.

madmodshoe
Dirt Forum Racer

Total posts: 89
posted April 13, 2003 01:55 AM
Check your carb. KP and other carb guru's will tell you that a properly tuned and jetted carb will run at normal temps. The fan is important as well as ductwork, but nothing on the front of the motor will overcome the wrong setup on the carb.

A2KY2K88
Dirt Forum Racer

Total posts: 86
posted April 13, 2003 02:59 AM
4 blade fans do NOT pull more air. They do let more air pass though because of the space between the blades. Use a 5 or 6 bladed fan. You can get away with a 4 blade on alcohol though. My point is that they definately do not pull more air.

FirstLight7
Dirt Full Roller

Total posts: 30
posted April 13, 2003 09:51 PM
Installed the 4 blade. Only got 4 laps in on a very heavy track before something broke (trans prob not motor). Temp jumped to 230 but not enough track time to tell too much.

It's got 30 lb cap on the radiator. 5/8" hole thermostat restricter. 80 jets in a Holley 4412 (93 octane pump gas). 50 percent reduction pulleys, etc. Maybe a whopping 9:1 compression on smog heads.

There are other things that I can work on to resolve the heating issue. I was hoping that throwing a fan at it would solve the problem (replaced a stock 7 blade with the 4 blade). The Afco dealer mentioned that the 6 blade moves more air. I've got a few different styles (steel and aluminum) setting around that I can try. Thanks for the feedback.

Scoot
Dirt Freak

Total posts: 330
posted April 13, 2003 10:23 PM
I would take the restrictor out and put 1 to 1 pulleys on. You want to push the water faster not slower.

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Scoot
Smith Racing Team
870-365-5989

jay116
Dirt Roller

Total posts: 25
posted April 13, 2003 10:46 PM
if you push the water too fast it won't cool either. My dad used to race a Super 6 Camaro and one of his tricks was to knock off every other vane on the water pump.
Look at it this way. The pump was designed to be on a motor that normally turns 2500 to 3500 rpm. On the track you are probably maintaining 4000. Thats why you want to slow it down. I would make sure you have good air flow through the radiator.

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Jason Boivin
http://www.rcracing-team.com

66jj
Dirt Freak

Total posts: 352
posted April 13, 2003 11:35 PM
50 % reduction pulley have never worked on a gas motor that ive seen. and i have tried it myself. 30 percent was ok. but a little too slow still.

go 1-1. i run a stat high flow mr gasket, all copper.

i run a stock long pump with a plate riveted on the back, i tried a long alum from speedway and had heating probs. took it off and they were gone again.

jeff

AC156
Dirt Freak

Total posts: 295
posted April 14, 2003 08:13 AM
I agree with Scoot. Take out the restrictor. we ran one early in the season last year and the car would run about 220. one night it went to 245. i took out the restrictor, and the rest of the year it stayed right around 200. go to the stewart water pumps website. they have a lot of tech tips for keeping a car cool. they also tell why people to have to run restrictors with the old style radiators, but NOT with the newer ones. http://www.stewartcomponents.com/html/tech_support/techtip3.asp

Quote from my College Physics book:
"Covection is heat transferred by the motion of a fluid or gas. Convection depends on a number of factors: The FASTER the fluid or air flow, the quicker the heat will be transferred....."

[This message has been edited by AC156 (edited April 14, 2003).]

towmandan
Dirt Maniac

Total posts: 110
posted April 14, 2003 10:12 AM
Ive ran for yrs. with about a 10to1 355 with 30% reduction a 2 row griffin rad. 20# cap long cat water pump no mods. to pump I used the 17in. fan from Day its cheap I run 5/8 restrictor but the deal for me was a homemade verry good fittng aluminum fan shroud.I also run the same carb you run to.Ive ran with no restrictor and it would stay cool a little longer like half way thru a race but then the longer we ran the hotter it would get so I came up with the combination im telling you about and it will run a 50 lap special and not get over 210 maybe 220 at the end of the race. Hope this helps ....towman

HRT187
Dirt Maniac

Total posts: 173
posted April 14, 2003 10:28 AM
quote:
Originally posted by AC156:

Quote from my College Physics book:
"Covection is heat transferred by the motion of a fluid or gas. Convection depends on a number of factors: The FASTER the fluid or air flow, the quicker the heat will be transferred....."

[This message has been edited by AC156 (edited April 14, 2003).]



Thats a nice quote but it's taken out of context a bit. you have to remember you have three convection systems.

Cool air to aluminum radiator
hot water to aluminum radiator
hot engine to cool water

You need to balance the last two in a fashion that allows the water to be cooled by the radiator. The quote you have is absolutely correct if you are trying to cool a solid aluminum radiator, you would want the most air blowing across it. You aren't trying to cool the radiator though, you are trying to cool the engine.

Classic heat transfer (ME-430 at my college) exam question.

HRT187
Dirt Maniac

Total posts: 173
posted April 14, 2003 10:29 AM
Almost forgot, on the restrictor... If you notice hoses on a Winston Cup car, they are typically around 12-16AN fittings and hoses. About the same size as the restrictor I've found works the best.

Monster
Dirt Maniac

Total posts: 135
posted April 14, 2003 05:22 PM
Cup engines(DEI, circa 2001) have restrictors everywhere, to balance out flow. 1/2", water pump in to block(to force more coolant into -10 lines running to middle of block). 5/16", front outlets of intake manifold (again, to force more flow toward rear of block and heads). Take water out of rear of intake with minimum of -8 lines. The total fluid outlet area of this setup is a hose with an I.D. of .76". So you can see that the normal radiator hose is grossly oversized for the job it does.
In my experience, 50% underdrive is too much. I have never been able to get temps to a reasonable level with it. I run the pump at 67% of crank rpm. Works for me, along with the DEI restrictor setup.

[This message has been edited by Monster (edited April 14, 2003).]

madmodshoe
Dirt Forum Racer

Total posts: 89
posted April 15, 2003 12:54 AM
The cooling system you are running is right in line with what most people run. If it is not the cooling system, then what? Lets start with what heat range are your plugs? What weight oil are you running? Has your 4412 had any mods or is it bone stock? What do your plugs look like? Ashy? Dark? Spotted? The plugs will tell you where the problem is. What is your timing set at? Do you run headers? All of these play into the cooling ability of the radiator.

FirstLight7
Dirt Full Roller

Total posts: 30
posted April 15, 2003 09:51 AM
I started with the 3/4" restricter. With the car relatively cool we looked in the radiator to see if the water/coolant was flowing. I revved the motor a little and we had a volume of water shoot 1 foot out the radiator (did this twice for good measure). Plenty of flow there so I went with the 5/8".

The R43TS plug reads to be in the range for the 'classic' plug. Timing is relative on this engine (read timed by ear). I tried to get it 36-38 total advance, all in by 2400 rpm but the timing marks may not be perfect on this one. On the mostly stock carb, I think if I went to larger jets that it might start blubbering out of the turns. It pulls strong for such a mild motor (limited mod w/headers).

I still have some basic things that I can add to the cooling system, biggest thing being a fan shroud. Methanol motors are so much simpler to cool. I was hoping for the quick way out by just changing fans but I certainly appreciate all the helpful suggestions!

towmandan
Dirt Maniac

Total posts: 110
posted April 15, 2003 10:13 AM
If your plugs look pretty good I would step up one size on the jets and hot lap see what it does I dont think one jet size will kill ya but could make it run a little cooler also depending on how much compression you have ad some good fuel might help a little too.

racnfool
Dirt Full Roller

Total posts: 38
posted April 15, 2003 12:00 PM
Check out the tech info from Stewart Components. They have cured cooling problems for many of the Dirt Forum users. They been in the business for many years, this is good info for all to read. Especially read all the tech tips on cooling systems, you may be surprised by what most people think is correct for circle track cooling. These guys have testing to back up their claims.
http://www.stewartcomponents.com/html/tech_support/techtip1.asp
Good luck
Racnfool


HRT187
Dirt Maniac

Total posts: 173
posted April 15, 2003 02:36 PM
I've read it and I've tried it and the restrictor works better for me..... the only thing I can think of about why Stewart says no restrictor is that maybe they already run a thermostat.

Racer14K
Dirt Freak

Total posts: 247
posted April 15, 2003 03:12 PM
Put a fan shroud on it and a plastic air dam off the bottom of the radiator.

rico 08
Dirt Freak

Total posts: 372
posted April 15, 2003 07:49 PM
If i read you're post right you say you timed it by ear?When i try this i'm always too fast,anyway i'd try a little less timing that should help you're heating problem.

madmodshoe
Dirt Forum Racer

Total posts: 89
posted April 15, 2003 09:29 PM
if you can, borrow someones timing light to get the job done right. 36deg. of timing will run fine while it has been my experience that 38 or 40 will make it run way hot. If you allowed to run racing gas that help a bunch! If it is to expensive then mix it 50/50 with your 93 octane. the standard octane rating for even a mild motor with that much timing would be in the range of 97/98 to 102. A fan shroud will do wonders for you fan and radiator, it might even get them a date up front! Sounds like you already know know what you need to do, you just haven't committed yet. Good Luck!

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