Stock 340 springs vs comp 901-16
Why would I need shims? Just to compensate for the stock springs being used?
Thanks!
Shimming is std. procedure for a valve job, that's all. Every time a seat and stock valve face are cut, the stem moves up in the head and raises the retainer. Shimming will
simply correct the installed height &/or let You tighten up the springs for a little better performance. The maximum recommended lift on the 901's is only .400"....even tho'
they list the load over the nose of a .450" lift @260#. The Red 340HP spring will accommodate .500" lift, and the rate of lift is what will stress the springs out, a set of
valve springs don't have a set "float at" RPM. An aggressive profile with .480" lift can float the same springs @5500 while a smooth profile with .520" lift won't float them
'till 5800-6000RPM , there's no such thing as "X-springs float at Y-RPM's", there are multiple factors that affect effective RPM range.
There is absolutely no reason not to shim them, and usually needed on used springs if You want to set them up for load vs. height. The 340HP's are rated by Mopar at
386#/inch, and are listed as the second choice for the 292/.508" cam! By Comp's own chart, the 901's aren't the "ideal" spring for that cam anyway, & list's the rate at
353#/inch.