Typical (acceptable?) loss of rocker ratio when loaded?

[Geoff2]

I find it hard to believe that aluminium rockers could deflect 0.030" or more & not break before you get to the end of the block...

[treyrags]

I find it hard to believe that aluminium rockers could deflect 0.030" or more & not break before you get to the end of the block...

This. And as someone pointed out already the majority of flex is probably in the pushrod. And the pushrod will flex different amounts unless you get the geometry exactly the same with each rocker comparison.

[Warp Speed]

My question is on a running engine does it flex back the opposite direction as it's unloading and add ratio?

The forces aren't really adding or subtracting ratio so to speak, just flexing the system.
And yes, for every action, there is an equal and opposite reaction. Unfortunately, it rarely happens at the same time or place. It is ever changing, both from cycle to cycle and through changing rpms, making it impossible to properly compensate.

OR so I've heard anyway.....

[pamotorman]

these problems go away with DOHC setup and why most high RPM engines use it as it removes a lot of these parts.

[Roundybout]

It's really amazing to me that a pushrod engine can turn 9-10,000 RPM and make power there. Springs oscillating, crankshaft harmonics, things flexibility, bending, compressing, expanding, cycle to cycle variables and on and on. To be able to best control that mess and win on Sunday, my hats off to you lol.

[GARY C]

My question is on a running engine does it flex back the opposite direction as it's unloading and add ratio?

The forces aren't really adding or subtracting ratio so to speak, just flexing the system.
And yes, for every action, there is an equal and opposite reaction. Unfortunately, it rarely happens at the same time or place. It is ever changing, both from cycle to cycle and through changing rpms, making it impossible to properly compensate.

OR so I've heard anyway.....

I am guessing that this is some what tracked on the spin tron?
Based on your response I am guessing you can not totally eliminate it or take advantage of it?

[fastblackracing]

I have found lift losses ranging from .018 to .030 ish.....
on engines built with middle of the road components....

One thing being left out of this discussion is the camshaft barrell bending under load which
I think is a major player in this lift loss scenario....

Most cams have a core diameter of 1 inch or less in alot of cases and when you
reverse the spring pressure against the rocker the cam sees 960# of pressure
at max lift with a 600# spring and 1.6 rockers.....

More than enough to bend that 1 inch or less diameter shaft that is supported by
2 cam bearings 5ish inches apart....

I was surprised to see how much lift I am losing on my last v6 engine when I first
started checking lift loss.( .025ish with T&D's and 650#)

In my case the cam base circle is around .930 and the core is less than that.

On my sons N2O SBF the Lift loss was round .018...but the cam core is larger and it has
900ish# pound open and 1.7 rockers......gross lift in the .840 range.

So Cam core size Matters.....

[turdwilly]

I have found lift losses ranging from .018 to .030 ish.....
on engines built with middle of the road components....

One thing being left out of this discussion is the camshaft barrell bending under load which
I think is a major player in this lift loss scenario....

Most cams have a core diameter of 1 inch or less in alot of cases and when you
reverse the spring pressure against the rocker the cam sees 960# of pressure
at max lift with a 600# spring and 1.6 rockers.....

More than enough to bend that 1 inch or less diameter shaft that is supported by
2 cam bearings 5ish inches apart....

I was surprised to see how much lift I am losing on my last v6 engine when I first
started checking lift loss.( .025ish with T&D's and 650#)

In my case the cam base circle is around .930 and the core is less than that.

On my sons N2O SBF the Lift loss was round .018...but the cam core is larger and it has
900ish# pound open and 1.7 rockers......gross lift in the .840 range.

So Cam core size Matters.....

That's an aspect I hadn't considered. Now that you mention it, the SBC cam I used is ground on a .900" base circle core. The SBF is ground on a standard base circle core. I had originally intended to run the LGM shafts on the SBF also, but I saw the same type of deflection lift loss on the SBF with the LGM rockers as I had experienced with the SBC, & I couldnt make the spring package work with the lower lift numbers, so I went with the Jesel rockers.