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Discussion Starter #1 (Edited)
Well guys....I finally figured out why my car has been overheating.

Let me back up here to give you the whole picture....

I used to have this 406 in another Nova with no overheating problems whatsoever. When I rebuilt this motor to put in my new sedan I changed a few things. I thought it would be nice to upgrade to some nice billet aftermarket pulleys so I went to my local performance shop and picked up a new crank/waterpump pulley made by Spectre. Boy did they look good!!

The problem is ever since then my engine temps would go out of control if the outside temp was 85+ and I would have to shut the car down if I was in too much traffic...200....205...210....215.....

Well....I recently re-measured my pulleys b/c someone mentioned they thought my new billet crank pulley was unusually small and thought this would cause overheating issues. So I went home to measure my new billet pulleys compared to my factory stock pulleys. This is what I found.......

New billet crank pulley= 6" in diameter
Old factory crank pulley= 8" in diameter

New billet water pump pulley= 6.5" in diameter
Old factory water pump pulley= 6" in diameter


This means I was underdriving my water pump 30%=not good. This is why my temps would get out of control in heavy traffic.

The box the pulleys came in only said "crank Pulley long water pump". No where on the box and even on there website does it state this is an underdrive pulley set up.
ALL I DID WAS CHANGE THE PULLEYS BACK TO STOCK PULLEYS AND ADD A 160 thermastat. The car stays at a 170 deg at all times now. No matter how much traffic I sit in and no matter what driving condition I put the car through. Not to mention the tranny gauge stays cooler too b/c it runs through the radiator.

I ABSOLUTELY DON'T UNDERSTAND WHY COMPANIES WOULD SELL A PRODUCT AND NOT DISCLOSE THAT THE PRODUCT IS AN UNDERDRIVE SYSTEM! I wasted my money and time on garbage as far as I am concerned. Not to mention the local hot rod shop didn't question it. Unbelievable!!


I just thought I would share my experience with you so you're not wasting you time trying to track down an overheating issue when all you have to do is change the pulleys out to a stock size.

Never...and I mean never will I ever buy another pulley without measuring to ensure they are stock specs.



CLIFF NOTES:: DON'T BUY AFTERMARKET PULLEYS WITHOUT MEASURING TO ENSURE THEY ARE THE SAME SIZE AS STOCK PULLEYS!!!
 

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Those underdrive systems are advertised to free up HP. It's amazing what they really do.
 

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thanks for the heads up.
it's amazing that we(myself included!) sometimes blindly follow the trends to improve our rides,but completely disregard all that R&D from the factory.i don't believe that there isn't room for improvement on our 25-44 year old rides,but sometimes i think it's easier to follow the "latest/greatest" trend without questioning it in terms of "WILL THIS PART IMPROVE MY CAR?".or "WHY IS THIS BETTER THAN THE ORIGINAL PART IT WILL REPLACE?".
just my 2 cents worth.
carl.
 

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I bought the exact same pulley ratios from March for my car. They were supposed to "free-up" HP. It overheated bad. I messed around with everything too and finally put the stock pulleys back on and had no overheating problems ever again. I have never known anyone who has had much success with the underdriven water pump pulleys. They must work for some applications or I don't think they would still sell them but I've never seen one yet.
 

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Good Info--- It's interesting how such a small change would alter the engine running temp 30+ degrees.... I guess size does matter..........
 

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This means I was underdriving my water pump 30%=not good. This is why my temps would get out of control in heavy traffic.
Good Info--- It's interesting how such a small change would alter the engine running temp 30+ degrees.... I guess size does matter..........
With the factory pulleys the pump is 33% overdriven. With the aftermarket pulleys the pump is 8% underdriven. The pump is going 44% faster with the factory setup, a large difference in flow.
 

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Dave, congrats on getting that one figured out...I know its been a pain in your behind for a long time:eek: ...Now get out there and enjoy riding in your rod without worrying about temp:cool: :)
 

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I have some summit cards that have been just burning a hole in my pocket. yesterday I was looking at pulleys and was ready to buy...thanks for the heads up I will double check my idea!
 

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If (probably should say "when") parts are made in China? They know nothing about overdrive or underdrive. The manufacturers that produce "global" parts do it for cheap labor and more profits. There will be very little or no application information. They know 6" pulleys will sell.

Glad you got it straighten out.. Too nice of a car for temp problems!!

Don
 

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Haha, crap. Now i need to go measure my pullies.... Thank god you posted on this issue. Hopefully i dont have a bunch of waisted money hanging on my car... Wouldn't be the first time. :rolleyes:

But thanks for the head up! Im just about to start up the engine for the first time in quite a while!

Rennskii :beer:
 

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With the factory pulleys the pump is 33% overdriven. With the aftermarket pulleys the pump is 8% underdriven. The pump is going 44% faster with the factory setup, a large difference in flow.
Mike, how did you come up with those numbers? I think you or someone post how to calculate them before but i can't find it. I am curious how much of a change occurs with a 8" crank and 6.5" pump pulleys.
 

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8 / 6 = 1.33 This is the 33%

6 / 6.5 = .92 This is 8% less

1.33 / .92 = 1.44 So the difference is 44%

You could have different diameters for your pulleys and can see what the ratio or percentage of overdriven(hopefully) speed is.

I just went out and measured mine and found out I'm at at 0%. (5" and 5"). I hope my oversized rad and hd electric fan and shroud will be enough to compensate for the slower coolant flow.
 
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