ZeeOSix

See the formula derived by Euler for columns:

http://en.wikipedia.org/wiki/Buckling

The Area Moment of Inertia (I) is a big player in column stiffness. As vettenuts has said, the pushrod OD and wall thickness determine the overall I value. Also, Modulus of Elasticity (E) is a factor ... so material properties does also play a role. Increase both I and E and you have a much stiffer pushrod.

wildcamaro

iTrader: (15)

No doubt...I'm sure the one piece construction of aftermarket pushrods also plays a role, albeit the two major factors are the ones you listed...I actually want to do a stress analysis of stock pushrods vs aftermarket ones but I cannot find a definitive answer on the wall thickness of a stock pushrod...I may have to sacrifice one for the greater good lol...most stock type aftermarket pushrods have an 80 thousandth wall thickness...I'm going to use a stock spring with the stock pushrod and probably use a comp magnum pushrod and 918 spring in the compairison...

ZeeOSix

When I upgraded the valve springs in my 2002 Z06 with PAC 1518 valve springs and the Comp Cams trunnion kit, I also upgrade the pushrods to Mantons. Vettenuts was the guy who recommended the Mantons. I went with the Series 3 #304, 11/32" dia x 0.120" wall. If you search this forum you'll find some of my old threads.

http://www.mantonpushrods.com/

vettenuts

iTrader: (4)

The point is, for steel, E is pretty much constant. There is no way to increase it so the variables that are left or length, OD and ID. If you break it down, length is constant because for any individual engine setup you can't alter the pushrod length without affecting lifter preload. That leave OD and ID. The ID will play a very minor role, even if the pushrod is solid and the ID is zero. Thus, OD is the controlling parameter. For harmonics, a non-constant OD (tapered pushrod) is the best way for control.

vettenuts

iTrader: (4)

Length and modulus are constant. Just plot out the OD to the fourth power minus the ID to the fourth power in Excel, you will quickly see how the stiffness is controlled by the OD.

Silver Sleeper

iTrader: (7)

holy hijack........