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Author Topic:   Fan Shroud Question
sleadhead44
Dirt Maniac

Total posts: 109
posted August 01, 2004 04:52 PM  
I have done EVERYTHING in all the posts to keep the water temp cool, but I was wondering, why most everyone says the fan should be 1/2 in and 1/2 out of the shroud. My fan and part of the fan spacer is 100% inside the shroud, and the car stays a little hot. Could this be causing my problem? Also, when you say 1/2 in and 1/2 out, Do you mean that the outer part (front most part) of the blades should be inside the shoud and the back of the blades should be outside the shroud? Thanks in advance for your replies!

5eRacing
Dirt Full Roller

Total posts: 36
posted August 01, 2004 04:57 PM  
i had the sam problem until i moved it half in and half out half the blade should be inside the shroud and half in side the shrous

I-B-RACIN
Dirt Maniac

Total posts: 132
posted August 01, 2004 04:59 PM  
put in a shorter spacer to get the fan half way out of the schroud run 1;1 pulleys big fan and the plate in the water punp so it dosnt cavitate

I-B-RACIN
Dirt Maniac

Total posts: 132
posted August 01, 2004 06:46 PM  
sorrry 5e posted same time

JohnG
Dirt Maniac

Total posts: 137
posted August 01, 2004 06:58 PM  
Its 2\3rds in the shroud and 1\3rd out of the shroud that is recommended.

eenfield
Dirt Maniac

Total posts: 116
posted August 01, 2004 07:14 PM  
Seems to allow more airflow. Not 100% sure why.

racer17j
Dirt Forum Champ
Total posts: 5390
posted August 01, 2004 09:04 PM  
After talking it over with my buddy, we are thinking that if the fan is in the shroud 100% then maybe it pulls cool air through the radiator, and then the air turns warm after passing through the rad. and the fan just blows that warm air around inside the shroud, and it never fully escapes causing the water temp to rise. Does this sound logical everyone?

neil rucker
Dirt Forum Champ
Total posts: 799
posted August 02, 2004 09:11 PM  
yeah

leapinlizard
Dirt Freak

Total posts: 402
posted August 03, 2004 01:14 PM  
With out being to technical, the air surrounding the outer most part of blades will not be able to move, this creates a higher pressure area right in front of the blades causing the air to stall. When a properly spaced blade scoops up air and pushes it forward a lower pressure area is left behind directly behind the blade. This low pressure area causes the slower moving(higher pressure) air to migrate toward the low pressure side of the blade allowing more air to be scooped up by the next blade coming. If the fan is to close or to far way from the shroud(the part surrounding only the blades) the same thing will ocurre but to a lesser extent.

You car may not be able to pull all the air it needs to exchange heat due to the fan spacing. I don't know what you mean by a "little hot" but it easy to try. You might try getting the fan within two inches of the radiator as well. This may or may not be possible with you current configuration.

JRB13
Dirt Forum Racer

Total posts: 80
posted August 03, 2004 02:29 PM  
IF YOU ARE HAVING PROB WITH OVERHEATING JUST BUILD YOU AN AIR BOX IN FRONT OF YOUR RADIATOR YOU CAN USE EITHER PLASTIC OR SHEETMETAL THAT WAY ALL THE AIR COMING IN WILL BE DIRECTED RIGHT INTO THE RADIATOR.

sleadhead44
Dirt Maniac

Total posts: 109
posted August 03, 2004 03:15 PM  
A little hot I meant it will stay at 220 at race speed, but it was at 240 in the make ready shoot, because it was only about 4 - 5 races after my heat and didn't cool down all the way. Went to 260 after the race, but didn't boil. It has a giant air box and it will pull a piece of paper to the grille just fine.

[This message has been edited by sleadhead44 (edited August 03, 2004).]

lazyracer5
Dirt Roller

Total posts: 10
posted August 03, 2004 04:08 PM  
UNDER DRIVE PULLY`S WILL OFTEN CAUSE PROBLEMS LIKE THIS.YOU MIGHT TRY PULLING YOURE TIMING BACK TO ABOUT 34 OR 32 DEG.ALSO LOOK INTO WATER RESTRICTORS.THEY ARE A CHEAP ENOUGH AT ONLY 6 OR 7 DOLLORS.ONE MORE THING IF YOU PULL YOURE TIMING BACK,REMEMBER IT MIGHT ALTER THE VACUUM.WICH WILL MEAN YOU NEED TO BACK OFF ON THE SECONDARY SPRING TENSION SO THE FOUR BARREL WILL WORK

5eRacing
Dirt Full Roller

Total posts: 36
posted August 03, 2004 04:49 PM  
I would not run 1 to 1 pulleys because it movies the water through the rad to fast and dose not give the water a chance to kool

waltonjr1
Dirt Forum Champ
Total posts: 516
posted August 03, 2004 06:11 PM  
Here we go again. LOL


sleadhead44
Dirt Maniac

Total posts: 109
posted August 04, 2004 09:00 AM  
Yeah I know Waltonjr1, LOL, all I wanted to know was about the shroud, not a whole list of suggestions. I read all the posts about this subject before building the car, and believe me, I have done them all, except for the fan spacing.

WesternAuto17
Dirt Forum Champ
Total posts: 569
posted August 04, 2004 09:41 AM  
It sure sounds like the shroud is working fine. If you're holding a sheet of paper on the grille, than the fan is sucking air thru the grille and radiator. That's the whole point of spacing the fan correctly in the shroud, so the fan pulls air thru the radiator and not from behind the fan.

I don't know what your trouble is, but it sure sounds to me like you have the airflow thru the radiator correct. 220 is right on the line. Seems to me that you almost have the problem licked, because if you can get that thing to race at 205 to 210, than it won't have trouble idleing before and after races.

Just as a point of reference, I run 36 degrees of timing, 1 to 1 pullies, a shroud ahead and behind the radiator, a 19" steel fan and a 180 degree T-stat. On a cool night, I have trouble getting heat in the engine. Have you looked into whether or not your carb is leaning out?

sleadhead44
Dirt Maniac

Total posts: 109
posted August 05, 2004 07:25 AM  
I haven't checked the carb yet, but I noticed when I went to measure the fan spacer, I could turn the fan around and the belt is just slipping on the water pump pulley. I better pull the alternator a little tighter and see what happens on Saturday. Could this be my problem, just a slipping belt? And should the water pump be able to turn over like that?

Flanndad
Dirt Freak

Total posts: 255
posted August 05, 2004 08:04 AM  
Hey sleadhead that's the same problem I had,
mine was caused by a slight power steering leak.
Power steering fluid was getting on the pulley and making the belt slip.
Before you tighten up the belt, remove it and clean the pulley up with brake cleaner, and to help slipping later I used my die grinder and went up and down on the inside v part of the pulley roughing it up very slightly to help grip the belt.

One more easy thing, I always jack up the front of the car some when topping off the radiator, let it run some before replacing the cap, this will help remove all air pockets in the engine.

    

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