Stud mount Roller Rocker ratio accuracy

General engine tech -- Drag Racing to Circle Track

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clshore
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Re: Stud mount Roller Rocker ratio accuracy

Post by clshore »

Three pivots on every rocker, pushrod end, center, and spring end.
Unless the pivot centers of all three line up perfectly, the actual ratio changes as the rocker rotates when opening the valve.
Complicated further if the rocker has mechanical screw adjuster on either end, as this moves the pivot center.
Complicated further if the pushrod is not perfectly parallel to the valvestem.
etc.

So any claimed ratio is at best a ballpark number, useful maybe for comparing relative performance of one set and another.

As others have posted above, be skeptical.

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Re: Stud mount Roller Rocker ratio accuracy

Post by BigBlocksOnTop2 »

Sweet P wrote:Our BBC T&D shaft rockers lift the valve .030" (yes that much!) more than I expected.

I called T&D and they said if I used the real springs valve springs vs the super light checking spring, that the lift would be right on.

Yep, that did it, there was .030" worth of flex in the rocker arm!

I still have a hard time believing that this actually works in a running engine but that was several years ago and its been working fine, the valvetrain is happy :o
Not sure where the extra lift came from but I too have saw this also, .563-.564 lift with the running springs and some where around .605 with the light ''checking springs''.
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Re: Stud mount Roller Rocker ratio accuracy

Post by Walter R. Malik »

When some company's advertise certain ratios, they give the average ratio throughout their given lift cycle therefore, at some point(s) throughout their travel the ratio will actually be greater than the advertised number.

Comparing rocker ratios from one to another is a "close value" at best, unless they are from the same manufacturer.
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Re: Stud mount Roller Rocker ratio accuracy

Post by Warp Speed »

The funny thing about this is, everyone is expecting accuracy from a stud mounted rocker! LOL
Shouldn't be used in the same sentence IMO!
Especially under dynamic loads!
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Re: Stud mount Roller Rocker ratio accuracy

Post by Warp Speed »

BigBlocksOnTop2 wrote:
Sweet P wrote:Our BBC T&D shaft rockers lift the valve .030" (yes that much!) more than I expected.

I called T&D and they said if I used the real springs valve springs vs the super light checking spring, that the lift would be right on.

Yep, that did it, there was .030" worth of flex in the rocker arm!

I still have a hard time believing that this actually works in a running engine but that was several years ago and its been working fine, the valvetrain is happy :o
Not sure where the extra lift came from but I too have saw this also, .563-.564 lift with the running springs and some where around .605 with the light ''checking springs''.
The added lift/ratio is built into the rocker. Some compensate for deflection, some don't..............................
You think there is a difference between checking springs and real ones, you should see the difference while under dynamic loads when the engine is running!
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Re: Stud mount Roller Rocker ratio accuracy

Post by Schurkey »

I was reading a book about a certain WWII aircraft engine--the huge R4360 four-row 28-cylinder.

The cylinder pressure was enormous at the exhaust-valve opening point. The force needed to pop the exhaust valve was enough to flex the entire rocker pivot area. Of course, this is an aluminum cylinder head/rocker pivot--but even so!

I can only imagine the amount of flex in the pushrod and rocker arm, when the structure the rocker mounts to is flapping back and forth from stress.
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Re: Stud mount Roller Rocker ratio accuracy

Post by MadBill »

I understand that the exhaust valve on a Top Fuel/FC opens not when the follower lifts off the base circle, but later, when the cylinder pressure drops to ~1,000 psi, at which point the solid 5/8" pushrod straightens out...
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