Saw this post on another site and figured Id share it since Bret actually brakes down the force exerted on the valve train from aftermarket springs/cam.
Alot of people question the use of hardened pushrods when swapping cams/spring and some wonder why thier setup isnt performing or why at a certain rpm the graph starts to look funny. Most of us dont have to worry about over-reving with an auto but alot of us turn the motors well past the stock 5400 shift points that the stock PR's are designed for multiply the 800 rpm shift extension with the extra forces of a 918 or 921 spring with aggressive xer lobes and its easy to see how the load is drastically increased from stock.
Just sharing some great insight into an overlooked topic.


"the LS makes more power from 5000rpm on up with better springs and pushrods. With no other changes it's amazing to see the gain at the track with that. Not to mention countless other motor combinations where they see this....

Anyways how about some math and some proof:





Little math:

GM HotCam Springs

101# @ 1.78" installed height
.525" lift, 332 rate = 275lbs
Now the pushrod sees that mulitplied by the rocker ratio = 440lbs

GM Stock LT1 springs (brand new)

85# @ 1.78" installed height
.446" lift, 373 rate = 250lbs
Roughly a 1.45-1.50 rocker arm ratio on stock rockers = 369lbs

So that's a increase of 20% alone, not to mention the increased pushrod forces that you would see with valve bounce and increased RPM. Lets just say going from 5400rpm to 6400rpm, now you see roughly 25-30% more pushrod forces due to the RPM. That works out to 50+% more force the pushrod sees.

All of those examples above buckled in various combinations and I know at the most we were looking at 480-540lbs that the pushrod was seeing, not to mention the added loads from RPM. Just one over-rev can cause the pushrod to turn into junk due to increased loads from the RPM. The loads increase from 5400-7400rpm by over 60%!!!! that right there is enough to bend the PR by itself!

You can either spend $70 more now to do it right or wait till that happens to you and spend the time and money to fix it later. Guys I'm all about bang for the buck and getting stuff for guys that doesn't cost a arm and a leg, but dam don't skimp in areas that will cost you money down the road and possibly cause MORE damage.

I guess the choice is up to everyone reading this, listen to someone with proof and physics or an OPINION.

Bret"

 

good info for us that dont browse much outside of pt.net

 

good info, I just replaced a pushrod that looked like that one, a little less than the one you got posted. That didnt fix my problem, I might have to pull the heads to see if its a lifter or bent valve for not changing my pr s