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Rob 930 Rob 930 is offline
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Join Date: Dec 2002
Location: Seattle
Posts: 661

It's a curiosity to some that cutting a helical coil spring (such as the one in your wastegate) will indeed stiffen it. Any design textbook on springs (such as Machine Design by Deutschman or Mechanical Engineering Design by Shigley and Mischke) will confirm this. There are formulas that explain it, but they're too much work to enter here. To convince yourself, take any old spring from a hardware store and measure how much force it takes to deflect it a known amount. Then cut it in half and measure again. You'll find it's stiffer - that is, it takes more force to move the spring the same amount when the spring is shortened. Think of it this way: if you have a long torsion bar and a short torsion bar (of the same diameter), which one is stiffer? It will be the shorter one. A coil spring is essentially a coiled up torsion bar, so a shorter coil is stiffer. Convince yourself...
Old 02-20-2009, 04:51 PM
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