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  #31 (permalink)  
Old 11-04-2011, 09:14 PM
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You see it wrong. Only the tip of the pushrod that rests in the lifter cup will always move the same distance as the cam lobe. The only way the other end can achieve the same lift is if the pushrod is pointed at the same angle at maximum lift as it is at base circle. That can only be done as described above.

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  #32 (permalink)  
Old 11-04-2011, 09:26 PM
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Quote:
Originally Posted by ScojoDak
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!
Consider an exaggerated example. Let's say the rocker is installed very high on the rocker stud, ie a very long pushrod. The rocker in this example is now pointing down about 45* in relation to the valve stem with the valve closed. Now the cam lobe comes around and starts to 'open' the valve. This pushes the tip of the rocker farther down and that rocker tip follows an arc that is already exaggerated and in effect doesn't open the valve very much at all as the rocker tip swings through its arc more to the side and away from the valve than down. Never mind that the rocker tip in this example will roll off the valve tip - this is just an exaggeration for explanation purposes.

Now position the rocker with a 'correctly' sized pushed so that the rocker fulcrum is 90* to the stem at mid-point and follow that through. It is obvious that the same cam lobe will result in opening the valve more than the first example.
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  #33 (permalink)  
Old 11-04-2011, 09:29 PM
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nofearengineer, Obviously! Using your analogy, how does the length of a pushrod change the lift?
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  #34 (permalink)  
Old 11-04-2011, 09:34 PM
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My head hurts. Goodnight fellaz.
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  #35 (permalink)  
Old 11-05-2011, 01:54 AM
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I think they are telling you. I looked up the word in the dictionary you said right beside the word ignorance. Lack of knowledge.
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Old 11-05-2011, 06:53 AM
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An interesting subject with lots of opinions. Those that understand after 3 pages of blogging will be better off than those that dont. If you are building a motor and the blocks been decked and with aftermarket heads, cam and lifters, you better do your home work. Cucumber 1949 puts it in prospective. All you need is a dial indicater and an adjustable pushrod and you will understand for yourself. It is really not necessary to call people names if you dont understand what they are trying to explain. I have said it before, this is a great forum and I am still willing to learn from others that post here.
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Old 11-05-2011, 09:00 AM
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I totally agree, I brought this issue up on another thread on millers mid lift rockers, who Mr. miller with others posting the reason behind this. I have been doing it wrong, and before next season I will find out how much I am off on length I have mine set up with leaving mark in the center(close) I don't no if it will change but I will check . There is no reason for getting mad just because you can't grasp a concept. And also there is a tremendous amount of knowledge on here, there are 4-5 regulars on here that I pay close attention to on here, but saying that I know there are alot more on here and If I don't agree I try to research it with some kind of backup before I run my mouth, because you will get shut down pretty quik
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  #38 (permalink)  
Old 11-05-2011, 11:00 AM
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Quote:
Originally Posted by 1932bantam
I totally agree, I brought this issue up on another thread on millers mid lift rockers, who Mr. miller with others posting the reason behind this. I have been doing it wrong, and before next season I will find out how much I am off on length I have mine set up with leaving mark in the center(close) I don't no if it will change but I will check . There is no reason for getting mad just because you can't grasp a concept. And also there is a tremendous amount of knowledge on here, there are 4-5 regulars on here that I pay close attention to on here, but saying that I know there are alot more on here and If I don't agree I try to research it with some kind of backup before I run my mouth, because you will get shut down pretty quik
While we're on the subject of sticking feet in mouths, I want to apologise for thinking you were telling stories when you first came here.

So, I apologise.
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  #39 (permalink)  
Old 11-05-2011, 11:19 AM
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Cobalt, thanks and accepted , As I said there is a lot of knowledge on here with different opinions, you are one of the 4-5 I mentioned that I think has there s--t together on here, I'm always learning something on here
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Old 11-05-2011, 11:46 PM
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rocker arm geometry....

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?
There's a famous quote that goes something like this- " There are those who know, those who don't know, and those who don't know they don't know". I'm new to this forum, and certainly don't have all the answers, but am here with an open mind trying to learn. Personal attacks and character assassination have no place here IMHO. For what it's worth, I know from personal measurements taken with different length pushrods in my NHRA Stock eliminator motor that lift at the valve DOES change as you change the pushrod length. The swipe pattern also changes both in its width and it's location from center on the valve stem tip. After reading Jim Miller's posting here, and a link to another paper written by him, I'm going to do more measuring and checking to try and optimize my valve train. I'm inclined to believe that there is reduction of drag possible as well as improvement in the valve following the cam profile with less loss due to wasted motion in the valve train geometry when it is optimized. Perhaps if you read Jim Miller's paper, link posted elsewhere here in another thread, the concepts might become more clear, agree or disagree. One way I learn is by trying to gain as much knowledge as possible from others, often smarter than I am, then by experimenting on my own car to see if I can make improvements. How, Sir, do you learn???
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  #41 (permalink)  
Old 11-07-2011, 11:24 AM
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Quote:
Originally Posted by Grant4060
There's a famous quote that goes something like this- " There are those who know, those who don't know, and those who don't know they don't know". I'm new to this forum, and certainly don't have all the answers, but am here with an open mind trying to learn. Personal attacks and character assassination have no place here IMHO. For what it's worth, I know from personal measurements taken with different length pushrods in my NHRA Stock eliminator motor that lift at the valve DOES change as you change the pushrod length. The swipe pattern also changes both in its width and it's location from center on the valve stem tip. After reading Jim Miller's posting here, and a link to another paper written by him, I'm going to do more measuring and checking to try and optimize my valve train. I'm inclined to believe that there is reduction of drag possible as well as improvement in the valve following the cam profile with less loss due to wasted motion in the valve train geometry when it is optimized. Perhaps if you read Jim Miller's paper, link posted elsewhere here in another thread, the concepts might become more clear, agree or disagree. One way I learn is by trying to gain as much knowledge as possible from others, often smarter than I am, then by experimenting on my own car to see if I can make improvements. How, Sir, do you learn???
On a stocker you have to check both the valve side and the pushrod side of the rocker for lost motion. This needs to be done at full spring pressure to account for the stud flexing. Also while doing this try a lash cap to see what direction the lost motion goes as this will give you indication about your valve length and it's position to the rocker stud. Once you've done all this you may have to get the cam reground to bring the lift up or down as needed to get back to legal lift. Getting the motion reduced on the pushrod side will reduce the effort to open the valve.

All that being said there is talk that stockers might be going to roller rockers next year which is a travesty in my eyes.
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Old 11-07-2011, 11:01 PM
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rocker arm geometry....

Engineczar, thanks for your reply! I agree, stock rule changes have created a lot of cost and more problems for all of us. The new rocker rule, if true, will cause other changes such as pushrod length, possibly cam changes, etc. Some engines will benefit more than others, there are always unintended or unforseen consequences with each further departure from the "original" rules.My present rockers are legally modified 502 big stud reinforced units that cost about $750. from Clark Holroyd, don't think I'll be stepping up to new rockers any time soon!! What became of the "grassroots of drag racing" concept, an entry level not requiring huge dollars but focusing on a racers ingenuity and tuning with a limited budget? I'd hate to total up all the parts I've had to throw at this thing, camshafts, converters, gears,rocker arms, tons of $$ and effort...
Re/ your suggestion of checking the valve side of the rocker arm for lost motion, how would I do that? What tools, procedure could I use? Although I could put a lash cap on to see what difference resulted, they are not legal to run at least until now. I'm thinking that maybe the valve is already longer than optimum, because it seems to me that as it gets longer it moves closer to the rocker stud. With a stamped rocker, wouldn't that result in the contact point moving in and reducing rocker ratio? Geometry was tough for me, even in school...lol and that was 50 years ago! Thanks for your ideas, they are appreciated! Keep 'em coming....
Grant
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  #43 (permalink)  
Old 11-08-2011, 07:28 AM
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geometry

To simplify: pushrod motion is linear (straight). Valve motion is linear. Rocker arm motion is radial. By using mid lift geometry, you are achieving the least amount of radial movement across the valve stem tip. This results in the most efficient motion for your rocker arm and the least amount of wear at the rocker and valve stem, period
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  #44 (permalink)  
Old 11-08-2011, 03:46 PM
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VERY interesting threads. After much scrutiny I am in total agreeance with this proceedure, wich means I now have developed geometry issues!!! It has also become obvious to me the offset location of certain valve stems, and why limiting the vertical perpendicularity of the pushrod needs to be taken into account. Since I don't have the cash for a shaft mount conversion, I'm wondering if getting rid of my current guide plates and opting for adjustable ones could limit this symptom. I also wonder if self-aligning rockers suffer from the same condition, or if they would naturally fix themselves to the correct mid-lift geometry position.

I noticed Manley has what looks like a raised/offset in some of the plates they sell.
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Old 11-08-2011, 04:52 PM
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geometry

Slewis, Its not the guide plates you need to focus on. At mid lift, half way through the lift cycle(of your cam), your rocker trunnion center, straight line through to the roller tip center, should be at 90* to the valve and or retainer. Its really very easy to accomplish. Adjusting the rocker is as simple as adjusting the pushrod up or down. you can use a adjustable pushrod checker and checker springs on one set of valves to set this all up.
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