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Rob 930 Rob 930 is offline
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Join Date: Dec 2002
Location: Seattle
Posts: 661
Originally Posted by TimT View Post

why introduce more variables? this is a simple system.. a force acting on a spring. i.e. the waste gate diaphragm acting on a spring.. If you take the spring, and make it shorter... the spring rate goes up! nothing suspicious or tricky... its what happens... so now you have your waste gate diaphragm acting on a spring with a higher rate... your low boost threshold is higher..
Tim, the only reason I did that was because of 911nut's comment, which brought up a condition worth considering. Though it is simple and true that a shorter spring is stiffer (for the same wire characteristics), that oversimplifies what's going on in a wastegate. What also matters in the wastegate is the force on the diaphragm, not just the spring stiffness. The spring in the wastegate must be compressed to the same degree, regardless of what spring is installed. Therefore it isn't necessarily true that a shorter spring will provide more force, one has to consider both the stiffness and the deflection of whatever spring is being used. There's no question that the shorter one will be stiffer, but if the longer (and less stiff) spring is able to be compressed enough, it may exert more force. So this isn't as simple as it looks...

What I would take back from this is that if you cut down a spring, be careful. Both the spring rate and the force at a given deflection will be changed.

Old 02-21-2009, 05:15 PM
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