12-10-2001, 03:12 PM
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CC Member
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Join Date: Nov 2001
Location: WPB,
FL
Cobra Make, Engine: CMC, Supercharged Ford 5.0 & all the toys.
Posts: 511
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Not Ranked
You could measure the stock and new pullies, and compute the ratio from that. (Measure to the inside of the groove). Also do the same for he crank pulley (if that changed) and multiply the two.
Underdrive ratio = (New-crank-dia. / Old-crank-dia) x ( old-alt-dia. / new-alt-dia. ).
Or you could just read what the pulley mfgr says it is.
Generally, 3-10% (0.97 - 0.90) is considered acceptable, but that depends on the car/motor and accessories.
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CMC Cobra, Ford 5.0, EFI, Vortech supercharged, T5Z, 8.8 rear, MII front, 4-wheel discs, A/C, stereo.
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