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

[BradH]

What do people feel is a typical, or "acceptable", loss of rocker ratio when measured w/ actual springs vs. soft checking springs?

I've got a set of 1.6 (advertised) extra-offset intake rockers and 1.5 (advertised) standard-offset exhaust rockers that measured 1.58 and 1.50 respectively w/ checking springs. When I put on the actual springs w/ 240 closed & 600+ open pressure and re-measure the actual lift, how much loss should I write off as "normal" deflection vs. looking into different rockers?

Thanks, Brad

[statsystems]

What do people feel is a typical, or "acceptable", loss of rocker ratio when measured w/ actual springs vs. soft checking springs?

I've got a set of 1.6 (advertised) extra-offset intake rockers and 1.5 (advertised) standard-offset exhaust rockers that measured 1.58 and 1.50 respectively w/ checking springs. When I put on the actual springs w/ 240 closed & 600+ open pressure and re-measure the actual lift, how much loss should I write off as "normal" deflection vs. looking into different rockers?

Thanks, Brad

Whose rockers are they?

They should measure bigger with checking springs than the advertised ratio.

[saleen385]

stud mount or shaft?

[andyf]

stud mount or shaft?

I'm pretty sure BradH is working with a big block Mopar with factory type shaft mounted rocker arms.

[A_VAS]

I just completed this exercise with a set of stud mount Crower Enduro stainless rockers.

They say 1.70 ratio
with checking spring I was getting valve lift indicating 1.79

Once installed with the real PAC 1255 spring at around 165 seated/ 400 open
I was getting right on 1.70

both done using a solid roller lifter

did they plan it this way? I dunno but it worked out

[anarot]

On my sbc the 1.65in/1.55ex Yella Terra shaft rockers came in at around 1.7in/1.55 with checking springs.

With 230lb seat and around 600lb open it cam back to 1.65 ratio exactly for the intakes and around 1.5 ratio for the exhausts.

This was only about 20 thou lift lost due to deflection but pushrods were .120 wall smith bros 7/16 items so probably reduced deflection a lot.

[BradH]

stud mount or shaft?

I'm pretty sure BradH is working with a big block Mopar with factory type shaft mounted rocker arms.

Correct, and they measured what they did regardless of what they're advertised as being.

My pushrods are .120" wall x 3/8" OD, so I'm hoping they'll be stiff enough not to contribute much to the loaded deflection when re-measuring with the real springs.

[statsystems]

I just completed this exercise with a set of stud mount Crower Enduro stainless rockers.

They say 1.70 ratio
with checking spring I was getting valve lift indicating 1.79

Once installed with the real PAC 1255 spring at around 165 seated/ 400 open
I was getting right on 1.70

both done using a solid roller lifter

did they plan it this way? I dunno but it worked out

That's how it SHOULD be.

If you have any questions, you can call Jesel. They will tell you they have an engineered amount of flex built into their rockers. T&D will tell you the same.

[BradH]

I just completed this exercise with a set of stud mount Crower Enduro stainless rockers.

They say 1.70 ratio
with checking spring I was getting valve lift indicating 1.79

Once installed with the real PAC 1255 spring at around 165 seated/ 400 open
I was getting right on 1.70

both done using a solid roller lifter

did they plan it this way? I dunno but it worked out

That's how it SHOULD be.

If you have any questions, you can call Jesel. They will tell you they have an engineered amount of flex built into their rockers. T&D will tell you the same.

I know that's how Crane designed their true race-spec rockers, too.

[statsystems]

I just completed this exercise with a set of stud mount Crower Enduro stainless rockers.

They say 1.70 ratio
with checking spring I was getting valve lift indicating 1.79

Once installed with the real PAC 1255 spring at around 165 seated/ 400 open
I was getting right on 1.70

both done using a solid roller lifter

did they plan it this way? I dunno but it worked out

That's how it SHOULD be.

If you have any questions, you can call Jesel. They will tell you they have an engineered amount of flex built into their rockers. T&D will tell you the same.

I know that's how Crane designed their true race-spec rockers, too.

Did you ever tell us the brand? Just curious.

[andyf]

Crane 1.60 rocker arm with a .445 lobe cam with checking spring and roller spring. About 0.030 of deflection in this case.

[Alan Roehrich]

You should understand how drastically valvetrain geometry will affect rocker arm ratio.

Most often it is not the rocker that is deflecting, it is either the fastener or the pushrod.

If the pushrod deflects it gets shorter.

Rocker arms are NOT constant ratio devices to begin with. The ratio varies throughout the arc, since the relationship between the pushrod cup, the fulcrum, and the roller at the valve is constantly changing while the rocker is in motion.

Altering the pushrod length 0.050" or less can often change net lift by as much as 0.020". You're simply changing the relationship of the pushrod end, the fulcrum, and the valve end of the rocker. Start the motion with the pushrod end higher or lower and you change where in the range of motion the rocker has a given ratio. This does affect shaft mounts as well, since you change the height of the pushrod end to adjust lash.

You could write a 20 page dissertation on the subject and barely cover it, there's no way to cover it here. Search this forum, we've discussed this several times, you may be able to glean enough information to get a solid grasp on it.

[Rizzle]

That's how it SHOULD be.

If you have any questions, you can call Jesel. They will tell you they have an engineered amount of flex built into their rockers. T&D will tell you the same.

But you can have fairly different load pressures for the same rocker, so while they have compensated for a given deflection, being on either side of typical (heavy valves/stiff springs or crazy light valves/beehives) will give you less or more deflection and resulting ratio.
Would be fairly easy to spec, something like 1.70 ratio @ 600 lbs open pressure, or similar.

[andyf]

Harland Sharp 1.60 rocker arm on the same BB Mopar as shown above. Same .445 lobe cam, same pushrod. Similar amount of deflection.

[BradH]

Alan: I actually have a much better grasp of the topics you listed above than you presume, based on my interpretation of your response.

Can you provide examples of unloaded vs. loaded net lift measurements from your builds, along with any supporting information on what you consider to be an allowable variance between the two measurements?