Roller rocker tip weights
02-03-2009, 01:01 PM
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Roller rocker tip weights Hey all im looking for any infor I can get on various roller rocker tip weights. Im particularly interested in the scorpions, so if you got some info please post up!
02-03-2009, 10:37 PM
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ya it seems so. Im considering getting the scorpions because alot of the local builders like em. Im not sure if I have enough spring pressure to avoid valve float though, which is why I wanted to know the tip weight.
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02-04-2009, 05:00 PM
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As far as Ive heard they have already been corrected, anyone?
Also what are these made of? I thought they were aluminum but I see references to steel?
Also what are these made of? I thought they were aluminum but I see references to steel?
Last edited by ZMONSTER!; 02-04-2009 at 05:16 PM.
02-08-2009, 12:27 PM
#11
This subject has been discussed many times in the past. Tip weight does not tell the accurate story concerning the effectiveness of rocker arm design. When your talking weight, it's all about the location of the weight.
I did some research on this subject a while back with the intent of calculating the mass moment of inertia for stock and other popular rocker arms. I dropped it but should pick it up again.
Just for grins, here are the 'tip weights' that I have:
Rocker type: (overall / tip weights)
Stock: 140.1 / 8.2 g
Crane 1.8: 149.8 / 22.8 g
These weights do not represent the weight actually seen by the valve train.
Here's how to calculate the mass moment of inertia of an IC engine rocker arm. http://www.tech.plymouth.ac.uk/sme/desnotes/valvet1.htm
I did some research on this subject a while back with the intent of calculating the mass moment of inertia for stock and other popular rocker arms. I dropped it but should pick it up again.
Just for grins, here are the 'tip weights' that I have:
Rocker type: (overall / tip weights)
Stock: 140.1 / 8.2 g
Crane 1.8: 149.8 / 22.8 g
These weights do not represent the weight actually seen by the valve train.
Mass Moment Of Inertia
"Mass moment of inertia is the relationship between the center of gravity of an object with irregular geometry and the rotational axis. The Mass Moment of Inertia of a solid measures the solid’s ability to resist changes in rotational speed about a specific axis. The larger the Mass Moment of Inertia, the smaller the angular acceleration about that axis for a given torque. The further the center of gravity is from axis of rotation, the higher the mass moment of inertia. The higher the mass moment of inertia, the more spring pressure needed to control the rocker arm instead of the valves. For example, every gram that is removed from the nose of a rocker arm (lower mass moment of inertia) operational RPM goes up significantly."
As you can see, as the Mass Moment of Inertia changes dramatically as the rocker arm is lightened, particularly at the nose. Obviously, there are limits to the amount of lightening possible, but when the weight is reduced, the capability of extending the engine RPM range increases. Keep in mind this finding also shows a tendency to improve valve spring life (as pointed out above, the spring is "less concerned" about the weight of the rocker, and "more focused" upon the weight of the valve).
Reference: Dr David J Grieve
"Mass moment of inertia is the relationship between the center of gravity of an object with irregular geometry and the rotational axis. The Mass Moment of Inertia of a solid measures the solid’s ability to resist changes in rotational speed about a specific axis. The larger the Mass Moment of Inertia, the smaller the angular acceleration about that axis for a given torque. The further the center of gravity is from axis of rotation, the higher the mass moment of inertia. The higher the mass moment of inertia, the more spring pressure needed to control the rocker arm instead of the valves. For example, every gram that is removed from the nose of a rocker arm (lower mass moment of inertia) operational RPM goes up significantly."
As you can see, as the Mass Moment of Inertia changes dramatically as the rocker arm is lightened, particularly at the nose. Obviously, there are limits to the amount of lightening possible, but when the weight is reduced, the capability of extending the engine RPM range increases. Keep in mind this finding also shows a tendency to improve valve spring life (as pointed out above, the spring is "less concerned" about the weight of the rocker, and "more focused" upon the weight of the valve).
Reference: Dr David J Grieve
02-08-2009, 12:35 PM
#12
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Stock LS rocker arms are lighter, stiffer and have less inertia (lower tip weight) than any commercially available rocker I know of. Therefore they take less spring to control which makes things easier on the valvetrain and/or allows higher rpm will less trouble. 7800+ with stock hydraulic lifters and rocker arms is doable. It has been done successfully. Springs, retainers and pushrods are not stock on that kind of setup.
If you must spend money on rockers, have Harland Sharp install their better bearings in your stock LS rockers.
Jon
If you must spend money on rockers, have Harland Sharp install their better bearings in your stock LS rockers.
Jon
02-08-2009, 03:09 PM
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Stock LS rocker arms are lighter, stiffer and have less inertia (lower tip weight) than any commercially available rocker I know of. Therefore they take less spring to control which makes things easier on the valvetrain and/or allows higher rpm will less trouble. 7800+ with stock hydraulic lifters and rocker arms is doable. It has been done successfully. Springs, retainers and pushrods are not stock on that kind of setup.
If you must spend money on rockers, have Harland Sharp install their better bearings in your stock LS rockers.
Jon
If you must spend money on rockers, have Harland Sharp install their better bearings in your stock LS rockers.
Jon
02-08-2009, 04:54 PM
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Thanks, and my name doesn't even start with a "P". 
Sometimes I think I'm talking to the wall on stuff like this. Some folks would be amazed at the places roller-tipped rockers are NOT used in some pretty high-end engines, and not because of rules. It's usually because the extra mass of the roller that doesn't do anything useful for MMoI or stiffness. The minor friction advantage of the roller tip is more than negated by the heavier (higher MMoI) roller.
From 455HP's post above, if you remove the non-rotating parts of the rockers which do not enter into the MMoI, the stocker is even better. We use titanium retainers to knock off 10 grams and then we put 12 gm back on with roller tips! Does that sound strange to anyone else?
Jon
Sometimes I think I'm talking to the wall on stuff like this. Some folks would be amazed at the places roller-tipped rockers are NOT used in some pretty high-end engines, and not because of rules. It's usually because the extra mass of the roller that doesn't do anything useful for MMoI or stiffness. The minor friction advantage of the roller tip is more than negated by the heavier (higher MMoI) roller.
From 455HP's post above, if you remove the non-rotating parts of the rockers which do not enter into the MMoI, the stocker is even better. We use titanium retainers to knock off 10 grams and then we put 12 gm back on with roller tips! Does that sound strange to anyone else?
Jon
02-08-2009, 05:01 PM
#15
<snip>From 405HP's post above, if you remove the non-rotating parts of the rockers which do not enter into the MMoI, the stocker is even better. We use titanium retainers to knock off 10 grams and then we put 12 gm back on with roller tips! Does that sound strange to anyone else?
Jon
Jon
02-08-2009, 08:39 PM
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I appreciate the comments fellas. I just get an urge to replace my stock rockers with rollers every time I pop the hood. I guess Ill just stick to the stockers for now.
Off topic some what, but would a set of roller rockers do anything toward quieting down the valve train? Thats another big reaon I consider the swap.
Off topic some what, but would a set of roller rockers do anything toward quieting down the valve train? Thats another big reaon I consider the swap.
02-09-2009, 04:42 AM
#19
Interesting aside, I bought one of the new Malibu's and the cover on the motor that makes it look pretty is about 1/4" thick sound deadening material (not plastic). Car is very quiet.
02-09-2009, 07:14 AM
#20
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So what about the wear on the guides that some people say will happen with bigger lift cams? BTW i changed back to stock rockers from Comp Cam rollers and cured my valve float, so a fan of stock.
