Valvetrain Geometry
How much have you seen springs change the RR? Is it mostly rocker deflection?
Yes. All rockers have some deflection which is why the actual unloaded ratio is higher than the nominal ratio. Or at least it should be.
You also have flex in the shaft and the pushrods, although if the pushrod is big enough you don’t see much loss when the system is loaded turning it over by hand.
I had some 5/16 heavy wall pushrods that came with a W2 engine I bought in 1986. I ran it like I bought it for two years and then I pulled it and went through it.
In 1991 I had it on the stand and I was using 3/8 pushrods I was just screwing around so I threw the 5/16 stuff back in and I saw the loss. And that was with about 255-260 on the seat. I forget how much it lost from unloaded to loaded but it was measurable.
Once I went to 300 on the seat I could not keep the adjusters tight. That made me chase a bunch of crap that wasn’t an issue.
I had to order some pushrods for my boss and at that time Walt Austin Racing was making pushrods. I was chatting with Walt and my junk came up and he said you can’t run that much spring load with all those funky angles on any straight 3/8 pushrod.
So he made up a set of double taper 3/8-7/16 pushrods and sent them and the issue stopped.
What was happening was the pushrods were bending and unbending so much it was like beating on the adjusters with an impact gun and it would cause them to come loose.
That drove me nuts for a while and all the whiz bang in gym shorts types said Walt was talking out of his hat and all that but they had to eat his hat when he was right.