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  #16 (permalink)  
Old 11-03-2011, 06:56 AM
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Quote:
Originally Posted by ScojoDak
Then what you need to do is write their technical staff that their 30+ years in the business is "regurgitating" incorrect info.


I did thank you and what they enphasize is "then these loads will balance in a straight down direction upon the valve, and NOT be over-arcing and shoving the valve against the guide, causing excessive friction, heat, wear and horsepower loss." They're basically saying the same thing as all the other valve train companies are saying. That is to keep the tip centered!



You're saying they're all wrong? Youre living in a bubble with ap72!

Eric, AP, and Cobalt are correct.

The ULTIMATE goal is to get the narrowest sweep pattern, the most available lift, and have it centered on the valve. Unfortunately it hardly ever comes out that way.
The reason is that the rocker stud and the valve stem are not parallel. If the valves are different lengths or are sunk more or less due to the valve job or if the rocker stud is off the distance from the fulcrum to the tangent point of the roller where it contacts the tip of the valve changes. Best case scenario for side loading and valve guide wear is the narrowest pattern which also gives you the most theoretical lift. I say theoretical because high spring pressures and pushrod flex influences the results. Because of tolerance stacks the pattern probably WILL NOT end up in the center of the valve which is ok. How far off center is too far? On an 11/32 stem diameter .08 either side of center is acceptable. If all you're doing is putting the pattern in the center of the valve regardless of sweep size then you're only fooling yourself into thinking you have the correct geometry.
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  #17 (permalink)  
Old 11-03-2011, 10:27 AM
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Succinct and accurate, Engineczar. IMHO, at least.

Not to put too fine of a point on this, but in another thread, I said that conceivably- if taken to the n'th degree- there is a distinct possibility of needing 16 different length pushrods, if you were working w/a set of heads that hadn't been correctly machined during various valve jobs, repairs, milling, etc.

Now, in practice, this is rarely if ever going to be the case. But if the heads weren't identical from valve to valve as to how far they were sunk during cutting the seats, or how much was removed from the tips during resurfacing them, or from the valve seat when they were resurfaced, this could be needed if precise enough measurements were made.

On a non roller-tipped rocker, this is much more a judgement call, as finding the "centers" of the rocker tips where they meet the valve tip is a problem. It has been said that a rocker roller would need to have a 2"-plus diameter to replicate the radius of a stock stamped steel SBC rocker arm.
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Old 11-03-2011, 06:19 PM
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Fellaz, all the guy wants to do is set his rockers correctly. He's not building a Nascar or NHRA Pro Stock motor where RPM's are near 9000+. I'm certain he doenst have all the precise measuring equipment and access to a machine shop to set it up like some of you are suggesting. GOOD GRIEF!
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Old 11-03-2011, 07:50 PM
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Getting a 'narrower' pattern uses the same basic tools as getting a 'centered' pattern. Moving the stud c/l and such isn't necessary if he's looking to optimize what he has, he's not looking (I don't believe) for any theoretical perfection.

A narrow pattern is preferred over a centered pattern, although they are not mutually exclusive. I have had narrow patterns that most times were centered as well. But if you are going to give up one and keep the other, give up perfectly centered for narrower.

Lunati has a procedure a little better than Comp. But even here the center is made to look more important than the width, although they don't come right out and say so.

Last edited by cobalt327; 11-03-2011 at 07:57 PM.
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Old 11-03-2011, 08:47 PM
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right on cobalt
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Old 11-04-2011, 06:29 AM
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Quote:
Originally Posted by cobalt327
Getting a 'narrower' pattern uses the same basic tools as getting a 'centered' pattern. Moving the stud c/l and such isn't necessary if he's looking to optimize what he has, he's not looking (I don't believe) for any theoretical perfection.

A narrow pattern is preferred over a centered pattern, although they are not mutually exclusive. I have had narrow patterns that most times were centered as well. But if you are going to give up one and keep the other, give up perfectly centered for narrower.

Lunati has a procedure a little better than Comp. But even here the center is made to look more important than the width, although they don't come right out and say so.
He can actually check it with nothing more than a dial indicator, adjust the pushrod and run the cam through one cycle, whatever pushrod length gives you the most lift will also give you the least scrub.
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Old 11-04-2011, 07:34 AM
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correct ap72
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Old 11-04-2011, 08:47 AM
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good stuff!!!!- 45 and still learning
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Old 11-04-2011, 11:06 AM
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Quote:
Originally Posted by 1932bantam
good stuff!!!!- 45 and still learning
This is a learning process for me as well. I had no reason until lately to question the "Comp Cams"-type methods.

It's a process of elimination of the BS from the good. Not always clear cut and certainly not everyone will agree w/what has been presented here. It's at least food for thought and will let someone come to their own conclusion as to what they think is worthwhile and what is better left alone.
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Old 11-04-2011, 01:43 PM
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If an off-center pattern causes wear on the valve guide, than all a wide, yet centered pattern does is ensure your valve guides are evenly worn.
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Old 11-04-2011, 02:26 PM
How fast is fast enough?
 
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An off center but very small wear pattern will minimize wear as the majority of your force is parallel to the valve stem
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  #27 (permalink)  
Old 11-04-2011, 02:46 PM
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Quote:
Originally Posted by cobalt327
This is a learning process for me as well. I had no reason until lately to question the "Comp Cams"-type methods.

It's a process of elimination of the BS from the good. Not always clear cut and certainly not everyone will agree w/what has been presented here. It's at least food for thought and will let someone come to their own conclusion as to what they think is worthwhile and what is better left alone.
X2 same here Mark. After Miller posted really got me thinking about all this.


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Old 11-04-2011, 06:55 PM
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Quote:
Originally Posted by ap72
whatever pushrod length gives you the most lift will also give you the least scrub.
How can pushrod length dictate "most lift"? It's the cam lobe that drives lift! You really are an idiot aren't you?
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Old 11-04-2011, 07:32 PM
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Quote:
Originally Posted by ScojoDak
How can pushrod length dictate "most lift"? It's the cam lobe that drives lift! You really are an idiot aren't you?
It dictates lift because the end of the rocker doesn't travel in a straight line, but rather an arc. By selecting a pushrod length such that at half cam lobe lift, the pushrod and rocker arm are at 90 degrees to one another, the net lift is maximized.

You'd probably learn a lot more here if you drop the name-calling. These guys do tend to know what they're talking about.
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Old 11-04-2011, 07:48 PM
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Tell me this. How can pushrod length influence lift? A pushrod is a FIXED length means of transfering mechanical motion from the cam lobe to the pushrod cup of the rocker. Whether the pushrod is 1" or 10" in length, it's going to transfer/move the SAME distance as the cam lobe height regardless of its angle to the rocker arm. It's the rocker arm ratio that influences valve travel by multiplying the cam lobe by the ratio of the rocker. This isn't rocket science people. Pull your heads out of the sand!

Regarding me using the term idiot, according to dictionary.com an idiot is "an utterly foolish or senseless person". Just calling it like I see it.
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