| I recommend using only stock front VTC springs in every application. My reasons are many, so I'll try to be as brief as possible. In my opinion, there probably isn't a more useless or misunderstood performance part made for the VG30DE(TT) than "upgraded" or "Heavy Duty" VTC springs. 1) Stock front VTC springs have one design purpose and that is to preload the VTC mechanism so that the entire gear doesn't move forward or rearward during VTC on/off events and upset the timing belt alignment - that's it, that's all that they do. 2) "Upgraded" or "Heavy Duty" VTC springs use thicker wire to make their spring rate higher than stock and this increases their installed load. 3) This thicker wire also increases the solid height of the springs to the point it is precariously close to the installed height within their working envelope. 4) If these springs are installed in a coil bind situation, they can lock the VTC mechanism and prevent VTC function entirely, or place too much load on the internal thrust surface and cause excessive wear - neither is good. Stock front VTC springs will never cause these problems.
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