Fan drive ratio - TheDieselGarage.com
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post #1 of 24 (permalink) Old 05-05-2007, 12:22 AM Thread Starter
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Fan drive ratio

I can't stand it any more. It has been 2 years since I suggested that the increased fan drive ratio on the LLY is culpable in the increased overheat arena. I have never tested the research on a test mule.

Background: based on my sieve of a memory, the FDR went from 1.29 LB7 to 1.48. FDR is just the ratio of the crank pulley dia to the fan pulley dia. In the LLY, the FDR was changed and the change was obvious in noise level. The reasoning to consider with the change, is that the fan now operates outside it's optimum zone, with several side affects to its increased speed. Higher noise, less air flow, higher parasitic drag, bigger centrifugal effect, reducing the axial nature of the fan design, possible over exertion of the viscous clutch resulting in further loss of energy in excess heat conversion (the clutch has cooling fins). Excess heat in the clutch is a conversion of crank work to heat production in the clutch. etc etc, blah blah. IOW, 20 HP more drag with less actual airflow.

Agree, don't agree...not important. Let's test this one out. A new LB7 fan pulley (pn 97226289) is under $400 new, perhaps less than $30 if someone can find a yard with one. I am asking for you guys to find one or 10 and try it out. The belt is the same IIRC. Anyone who can find these used, PM me, I'll buy it .

And please don't bring up electric fan conversions, I'd like this thread to stay open.

Michael
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post #2 of 24 (permalink) Old 05-05-2007, 02:10 AM
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So why didnt you just go to the local junkyard and rob an LB7 of its fan pulley?
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post #3 of 24 (permalink) Old 05-08-2007, 11:41 PM Thread Starter
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If anyone can find an LLY and LB7 fan pulley, I will model and machine some duplicates.

We can go from there. I am not sure how difficult that will be, but I am willing to give it a try.

Tom, i think my yard roaming days are over.

Michael
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post #4 of 24 (permalink) Old 05-09-2007, 12:15 AM
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Ah, darn. Yardin' can be fun, too. You never know what you'll find.
I just figured that would be the easiest way to find one.
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post #5 of 24 (permalink) Old 05-09-2007, 12:16 AM
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The local Boneyards in the Phoenix area are mainly networked now. While there are a few "u-pick-it", most can be called and they will have it pulled for you for pickup. I get alot of Jeep items and parts for experimenting on other vehicles. This is considerably cheaper then modeling and machining. As far as time, a phone call and then pick it up later sometime while I am out and about.

;-)
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post #6 of 24 (permalink) Old 05-09-2007, 12:25 AM Thread Starter
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"modeling and machining", because if my reasoning holds water, i will probably manufacture a version. That's what I was getting at. Maybe I will make some calls. i just have a feeling there aren't a lot of duramaxes in the boneyard with good front end parts.

Michael
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post #7 of 24 (permalink) Old 05-09-2007, 12:26 AM Thread Starter
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The LB7 is 97226289
LLY is 97309640

If they are used on another motor, that would make it easier to find.

Michael
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04.5 GMC 2500HD SRW LLY

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post #8 of 24 (permalink) Old 05-09-2007, 12:54 AM
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I know that they can cross reference factory numbers so you should be able to give those numbers. They can quote a price on the phone also. My experience with the online ordering / questionaire is that they do not respond. Phone works best.

My experience is that 2 years and older is best for success on getting parts. Less then 2 years is hit and miss. So I would expect success for an LB7 and an 04 LLY. Doesn't hurt to try ;-) Also an existing unit makes it easier to prep up a production run if you are going that route.

;-)
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post #9 of 24 (permalink) Old 05-09-2007, 12:57 AM
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Quote:
Originally Posted by killerbee
"modeling and machining", because if my reasoning holds water, i will probably manufacture a version. That's what I was getting at. Maybe I will make some calls. i just have a feeling there aren't a lot of duramaxes in the boneyard with good front end parts.
I had someone make me a 16% smaller waterpump pulley for my highly modified jeep. I needed more air across the rad at idle. The vehicle in motion was fine. Ths also allowed me to have a faster water exchange through the head. (I know that the waterpumps are gear driven for these diesels so not the same)

I went with aluminum for the pulley but found that the belt mixed with running in the sand dunes was eating at the belt section of the pulley. (excessive wear) I have had it sent out to be chromed on the belt area only to eliminate the wear issue.

;-)
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post #10 of 24 (permalink) Old 05-10-2007, 04:43 AM Thread Starter
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2 more pieces of the puzzle.

1. parasitic power loss increases with the cube of the rpm increase.

HP2=HP1 (rpm2/rpm1)^3. it is the rpm of the fan that applies. So a 20%increase in rpm (1.20 factor) results in a parasitic drag increase of 72.8%, or 1.20^3. If the LB7 drag loss was 30 HP, then the LLY is 52 HP.

2. Fan tip speed must be kept under 14,000 fpm for optimization, under 16,000 fpm (180 mph) to avoid operation near stall. Do the math on a 21" fan with a 4600 rpm speed, over 25,000 fpm. We have the added complication of not being direct drive, instead viscous slip drive. Imagine the amount of heat converted from rotational work in the clutch.

Michael
Vehicle Systems Engineer/Professional Tuner
04.5 GMC 2500HD SRW LLY

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