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Wer bremst verliert
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,767
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Belt size when changing pulley size?
Hi all,
This is a technical question but not Porsche-specific... I am installing a smaller pulley on my supercharger (in a 911...) and want to calculate the new belt size instead of ordering a bunch of sizes... Here's the diagram below...  Pls check my logic/math: If the pulley is 9mm smaller in diameter, then the outer diameter the belt needs to wrap around the pulley is 14mm smaller... old pulley diameter = 73mm Pi = 3.14 Pulley wraps around 1/2 of pulley Pi*73/2 = 114.6 new pulley diameter = 64mm Pi*64/2 = 100.6 Difference = 114.6 - 100.6 = 14mm Now, since the outer edge of the pulley is also 4.5mm closer to the crank does that also mean each "leg" of the belt must also be 4.5mm shorter? For an effective shortening of 14mm + 4.5mm + 4.5mm = 23mm? The belt on there now is a PK1300, which I believe means a 1300mm length. Thanks!
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2007 911 Turbo - Not a toy 1985 911 Cab - Wife's toy 1982 911 3.2 Indiash Rot Track Supercharged track toy 1978 911 3.0 Lichtbau toy "Gretchen" 1971 911 Targa S backroad toy |
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02-02-2010, 07:19 PM
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Registered
Join Date: Sep 2008
Location: Rio Rancho, New Mexico
Posts: 200
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14mm shorter is correct. Forget the 4.5mmx2.
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Doug Was 2.7racer. '76, 2.7 w/Webers, JE pistons, Solex cams. Elephant bushings front & rear, 23mm & 28mm torsion bars, big brakes front & rear, Pertronix. Track car. '85 3.2 stock, Orient red, comfy street car. |
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02-02-2010, 08:43 PM
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Wer bremst verliert
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,767
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Thanks!
__________________
2007 911 Turbo - Not a toy 1985 911 Cab - Wife's toy 1982 911 3.2 Indiash Rot Track Supercharged track toy 1978 911 3.0 Lichtbau toy "Gretchen" 1971 911 Targa S backroad toy |
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02-03-2010, 02:10 PM
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