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Old 09-19-2008, 06:40 PM
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sbc WP pulley diameter

I've read and read about underdrive pulleys.......no dimensions given....I don't know what I have....so someone please tell me what the diameter of a STOCK 283 sbc waterpump pulley is.
thanks.

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Old 09-19-2008, 08:36 PM
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sbc WP pulley diameter

that a old pulley ?, it's big if it's say early 60's,but to under drive it , you swap out the crank pulley , your already at a under drive state with that old big pulley you have .
most chevy's water pumps now are smaller ,turning pump faster .
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Old 09-19-2008, 11:45 PM
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I just went out to the garage and measured ....7"
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Old 09-20-2008, 05:17 AM
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I have a billet aftermarket WP pulley that measures 6 1/2" diameter and the crank pulleys are also 6 1/2". Is that an underdrive condition?
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Old 09-20-2008, 06:40 AM
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no, that's a one to one ratio....
cicumference inches of the pulleys is the same....

a under drive ratio example (less than 1 to 1 ratio) would be when the wp pulley has only completed one 360* revolution while the crank pulley has completed a full 360* revolution plus say 36* additional due to the cicumference inches difference...

{arse backwards to your question because it is actually "over-drive ratio" (more than 1 to 1 ratio) example but:}
just think about the gears on a 10speed bicycle.... depending on how big is the diameter of the rear gear, how far does the crank gear have to move to complete one rear gear revolution...
if the rear gear was a bigger diameter than the crank gear it would be a under drive ratio

many cars do have and need a overdrive pulley ratio, helps cooling in traffic with the AC running full blast and a bit to small radiator as a example...

Last edited by red65mustang; 09-20-2008 at 06:50 AM.
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