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Lightning Forums
2nd Generation
stock lightning lower crank pulley or supercharger pulley
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<blockquote data-quote="throttle jockey" data-source="post: 11352887" data-attributes="member: 54243"><p>SVT Blackout... I prefer to refer to pulley ratio when discussing pulley combinations. In my opinion this is much easier.</p><p></p><p>To determine the pulley ratio all you have to do is divide the diameter of the lower pulley by the diameter of the upper pulley. For example, the OEM lower pulley measures 7.5" and the OEM upper pulley measures 2.93" (on a Lightning, the 02-03 HD is slightly larger). </p><p></p><p>7.5" / 2.93" = 2.56:1 </p><p></p><p>What this means is that every one revolution of the lower pulley the upper pulley makes 2.56 revolutions. Swapping pulleys changes this ratio. Obviously, the more revolutions of the upper pulley, the more air the S/C is flowing at a given RPM. </p><p></p><p>Aftermarket lower pulleys generally increase the diameter of the pulley in 1/2" increments which produce two additional pounds of boost.</p><p></p><p>OEM lower = 7.5"</p><p>2# lower = 8.0"</p><p>4# lower = 8.5"</p><p>6# lower = 9.0"</p><p></p><p>To illustrate my point from an earlier post I made:</p><p>9.0" (6# lower) / 2.93" (stock upper) = 3.07:1 pulley ratio</p><p></p><p>Or, if you swap both the upper and lower:</p><p>8.5" (4# lower) / 2.75" (smaller aftermarket upper) = 3.09:1 pulley ratio</p><p></p><p>As you can see, the pulley ratios are essentially the same, just different methods to get to the same pulley ratio.</p><p></p><p>I hope this gives you a better idea :thumbsup:</p></blockquote><p></p>
[QUOTE="throttle jockey, post: 11352887, member: 54243"] SVT Blackout... I prefer to refer to pulley ratio when discussing pulley combinations. In my opinion this is much easier. To determine the pulley ratio all you have to do is divide the diameter of the lower pulley by the diameter of the upper pulley. For example, the OEM lower pulley measures 7.5" and the OEM upper pulley measures 2.93" (on a Lightning, the 02-03 HD is slightly larger). 7.5" / 2.93" = 2.56:1 What this means is that every one revolution of the lower pulley the upper pulley makes 2.56 revolutions. Swapping pulleys changes this ratio. Obviously, the more revolutions of the upper pulley, the more air the S/C is flowing at a given RPM. Aftermarket lower pulleys generally increase the diameter of the pulley in 1/2" increments which produce two additional pounds of boost. OEM lower = 7.5" 2# lower = 8.0" 4# lower = 8.5" 6# lower = 9.0" To illustrate my point from an earlier post I made: 9.0" (6# lower) / 2.93" (stock upper) = 3.07:1 pulley ratio Or, if you swap both the upper and lower: 8.5" (4# lower) / 2.75" (smaller aftermarket upper) = 3.09:1 pulley ratio As you can see, the pulley ratios are essentially the same, just different methods to get to the same pulley ratio. I hope this gives you a better idea :thumbsup: [/QUOTE]
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2nd Generation
stock lightning lower crank pulley or supercharger pulley
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