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Old 03-18-2012, 04:49 PM   #16
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Default Re: Valve Train/Cam Design

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Originally Posted by OldRusty View Post
Wouldn't a higher ratio help the valve spring keep the lifters on the cam by multiplying its pressure for more control? Kind of a catch 22 question.
Yes it would. Question, does the rocker have enough pivot length to move the pushrod cup far enough away from the fulcrum so energy from the pushrod rotates the rocker, rather then try and rip it out of the head.

Also with a higher ratio rocker every slight movement from the lifter/pushrod is transfered to the valve. Do we have large enough core sizes, base circles, lobes to allow them to be ground percise enough for a proper valve path with a high ratio rocker.
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Old 03-18-2012, 04:52 PM   #17
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Default Re: Valve Train/Cam Design

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Dont agree. They make rev kits if you just wanna keep the lifter on the cam. Prostock valvetrains design the system so the lifter leaves the cam over the nose for more lift and keep pressure off the nose of the cam.

Valve springs job is to make the valve change directions. Do we really want to have the same valve path for the entire rpm band?
Rev kits are not valve springs. Valve springs are valve springs. PS valve trains aren't the only ones incorporating controlled loft, but IMO that's an entirely different conversation. Ideally, any lifter should see zero presure over the nose if everything is designed correctly.
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Old 03-18-2012, 04:53 PM   #18
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Default Re: Valve Train/Cam Design

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It would seem that way, but 150# with a 2:1 rocker would essentially be the same as 200# with 1.5:1. The lifter needs X amount of pressure to stay on the lobe, whether it's from a 2:1 rocker, or 1.5:1. By using rocker ratio you can lighten the spring (mass) and your lifter acceleration on the lobe can be less and more easily controlled. That's one school of thought.
This is why spring RATE becomes more important with the higher ratio stuff since it produces more lift and accelerates the valve faster and still has to control the direction change of the valve/retainer/locks and also the spring mass. I don't have the answers, just theories in my head.
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Old 03-18-2012, 04:55 PM   #19
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Default Re: Valve Train/Cam Design

I'd like to find a spring with 100 on the seat and 1500 open.
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Old 03-18-2012, 05:05 PM   #20
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Default Re: Valve Train/Cam Design

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This is why spring RATE becomes more important with the higher ratio stuff since it produces more lift and accelerates the valve faster and still has to control the direction change of the valve/retainer/locks and also the spring mass. I don't have the answers, just theories in my head.
I aree. Two things have to happen...the lifter has to stay under control over the nose, and the valve can't bounce off the seat. Any more spring pressure than it takes to accomplish those two things I think could be considered parasitic.
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Old 03-18-2012, 05:06 PM   #21
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Default Re: Valve Train/Cam Design

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I'd like to find a spring with 100 on the seat and 1500 open.
Just increase installed height til you have your 100# seat, I don't think the results would end well.
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Old 03-18-2012, 05:28 PM   #22
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Default Re: Valve Train/Cam Design

One problem is that there is no magical design. Everything discussed here is subject to the design of the whole system in terms of component weights, geometry, and rpm ....... just to name a few.

We can't say this way is better than that way as a mandate.... because for what application, design of system, and rpm?

Very complicated issue.
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Old 03-18-2012, 05:36 PM   #23
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Default Re: Valve Train/Cam Design

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Originally Posted by shawns engines View Post
Dont agree. They make rev kits if you just wanna keep the lifter on the cam. Prostock valvetrains design the system so the lifter leaves the cam over the nose for more lift and keep pressure off the nose of the cam.

Valve springs job is to make the valve change directions. Do we really want to have the same valve path for the entire rpm band?
The nose of the cam is not where the "high pressure" is....unless it's not running.

But, that being said, I think we could all agree that the principle job of the valve spring is to precisly control the relationship between the lifter and the lobe. (whether the lifter is always on the lobe or not) So, anything that can be done to lower the reaction force on the lifter shoul make it possible to use "lighter" valve springs.

Last edited by Lobes; 03-18-2012 at 05:39 PM.
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Old 03-18-2012, 05:37 PM   #24
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Default Re: Valve Train/Cam Design

I think the term 'high ratio' is subjective. Why would 1.5 be considered low and 1.9 be considered high? Why isn't 1.8 or 1.9 considered moderate? Because General Motors only came with 1.7 on a bbc in 1965?

I don't think we should get caught up in a number like that and calling it high, or low.

If I want a particular lift at the valve per deg.... you may not get there but with a particular ratio of multiplication.... it just is what it is.
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Old 03-18-2012, 05:40 PM   #25
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Default Re: Valve Train/Cam Design

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Originally Posted by Lobes View Post
The nose of the cam is not where the "high pressure" is....unless it's not running.

But, that being said, I think we could all agree that the principle job of the valve spring is to precisly control the relationship between the lifter and the lobe. (whether the lifter is always on the lobe or not) So, anything that can be done to lower the reaction force on the lifter shoul make it possible to use "lighter" valve springs. Thoughts?
All this stated, can we make a spring 'act' with higher pressures if one lobe has more acceleration than another?

In other words, with greater acceleration does the reaction force increase requiring less spring rate in the end? It's like circular reasoning
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Old 03-18-2012, 05:47 PM   #26
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Default Re: Valve Train/Cam Design

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Originally Posted by Chris Uratchko View Post
All this stated, can we make a spring 'act' with higher pressures if one lobe has more acceleration than another?

In other words, with greater acceleration does the reaction force increase requiring less spring rate in the end? It's like circular reasoning
Well we know what excessive pressure/rate does to pushrods... It's probably safe to say most enignes have more than one "valve spring" per valve.
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Old 03-18-2012, 05:47 PM   #27
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Default Re: Valve Train/Cam Design

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Originally Posted by Chris Uratchko View Post
All this stated, can we make a spring 'act' with higher pressures if one lobe has more acceleration than another?

In other words, with greater acceleration does the reaction force increase requiring less spring rate in the end? It's like circular reasoning
With greater acceleration at the lifter you would need more spring to control the greater inertial forces produced. F=ma

Last edited by Lobes; 03-18-2012 at 05:50 PM.
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Old 03-18-2012, 05:49 PM   #28
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Default Re: Valve Train/Cam Design

Quote:
Originally Posted by Chris Uratchko View Post
I think the term 'high ratio' is subjective. Why would 1.5 be considered low and 1.9 be considered high? Why isn't 1.8 or 1.9 considered moderate? Because General Motors only came with 1.7 on a bbc in 1965?

I don't think we should get caught up in a number like that and calling it high, or low.

If I want a particular lift at the valve per deg.... you may not get there but with a particular ratio of multiplication.... it just is what it is.
If we could get the cam and lifter for a pushrod engine to do what we wanted the valve to do, would you rather see a 1:1 rocker, or still use some ratio?
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Old 03-18-2012, 05:51 PM   #29
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Default Re: Valve Train/Cam Design

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Originally Posted by Lobes View Post
With greater acceleration at the lifter you would need more spring to control the greater inertial forces produced. F=ma
or more ratio
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Old 03-18-2012, 05:52 PM   #30
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Default Re: Valve Train/Cam Design

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Originally Posted by Chris Uratchko View Post
One problem is that there is no magical design. Everything discussed here is subject to the design of the whole system in terms of component weights, geometry, and rpm ....... just to name a few.

We can't say this way is better than that way as a mandate.... because for what application, design of system, and rpm?

Very complicated issue.
this...
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