Aftermarket LSx Rockers and Valvetrain Stability... Dyno Results inside.
09-17-2010, 03:46 PM
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Aftermarket LSx Rockers and Valvetrain Stability... Dyno Results inside. You've asked for it, here it is. I've worked with hundreds of people over the years to solve their missing power and valvetrain woes... Last weekend I finally had a perfect opportunity to do a back to back comparison of roller rockers vs. factory GM rockers. The results may suprise some of you but for those of us who do this everyday, there were no suprises, only confirmation.
See the writeup and results here:
http://blog.thunderracing.com/2010/0...d-valve-float/
Enjoy,
Shane
See the writeup and results here:
http://blog.thunderracing.com/2010/0...d-valve-float/
Enjoy,
Shane
.. I can't wait to get my 243s and trunions on!
09-17-2010, 04:33 PM
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I read the article and have a few questions..
What springs were being used?
Were the new Manton pushrods stock diameter?
Were the pushrods being used with the YT stock diameter?
What springs were being used?
Were the new Manton pushrods stock diameter?
Were the pushrods being used with the YT stock diameter?
09-17-2010, 08:36 PM
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FWIW, the original pushrods were indeed stock diameter. The springs were whatever is normally installed on the TFS as cast 225 heads.
I have actually made this swap many times with various brands of aftermarket rockers and my point here is definitely not to bash Yella Terra or any other brand. The post is purely educational and reflects what I see on a daily basis. I help many, many customers over the phone and via this site with similar issues such as this. This was just one instance of many that I was acually able to post because the swap was actually done on the dyno.
Thanks,
Shane
I have actually made this swap many times with various brands of aftermarket rockers and my point here is definitely not to bash Yella Terra or any other brand. The post is purely educational and reflects what I see on a daily basis. I help many, many customers over the phone and via this site with similar issues such as this. This was just one instance of many that I was acually able to post because the swap was actually done on the dyno.
Thanks,
Shane
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09-17-2010, 08:57 PM
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Shane
09-17-2010, 11:04 PM
#9
Nice writeup Shane, but I would like to include some information that the average customer may not know or understand that is important to long term durability. If it's a race only application that isn't driven on the street, then disregard the information below. If it's driven on the street, then you need to understand this information.
The problem with a stock GM 15 degree rocker (the 12 degree rocker is different) is that over .550" lift the rocker starts to scrub. This "scrub" can damage the valve tips and will cause wear to the bronze guides (powdered metal guides tend to last, but not always) We have seen this on EVERY type of 15 degree head made including AFR, Dart and even GM when bronze guides are installed (stock GM has powdered metal guides).
Most everyone understands how roller rocker geometry should work. As the trunion is raised, the sweep width is decreased, side loading is decreased, lift is increased and life is good. This is called "full arc" type geometry and is what most roller rocker manufacturers who know what they're doing strive for, like Jesel.
As you shim up a GM stock rocker you decrease the sweep pattern, but you INCREASE scrub and increase lift. The increase in lift is a good thing, and is part of the power gain you are seeing. You have to remember that a stock rocker GAINS ratio as it lifts the valve, unlike a roller rocker. As the stock rocker is shimmed up, it gains even more ratio.
The increase in scrub is a disaster waiting to happen. If you remember the problems AFR had when they had some soft valve tips and the valves would get worn down to the locks, this is the same thing you will see long term with shimming up stock rockers, on any head, including the TFS heads.
A stock GM rocker needs to work like a rocking chair works, or like a gear meshes, and is what the stock rocker does well up to about .550" lift, this is called "half arc" geometry. The sweep pattern looks wide, but is simply a function of how a stock rocker must operate. Everything past "half arc" results in the tip of the rocker arm DRAGGING itself across the top of the valve, not good for valve tips or guides.
If you look at WHERE the rocker scroll is contacting the valve at full lift (.600" or so) you will see it's on the VERY TIP END of the rocker scroll with a contact pattern about .010"-.020" wide. This narrow contact patch combined with maximum spring pressure at maximum lift puts the PSI (pounds per square inch) of the contact patch in the stratosphere. (FYI, an LS7 rocker at .650" lift has more contact patch than a LS1 rocker at .600")
Think about having a rocking chair on your wifes new hardwood floor, rock all the way forward to the very tip end of the rails, and then take your feet and push the chair backwards digging the tip of the rails into the floor. This is what a stock rocker does past about .550" or so, the more it's shimmed, the SOONER in the lift cycle this occurs.
The TFS heads come with springs that check at 160 seat 450 open. If you attempt to run stock rockers you need to install powdered metal guides to eliminate the guide wear, and install springs that are no more than 400 open, like the "platinum" springs that TEA sells, they check at 160 seat 400 open. This lesser open pressure makes life easier on the valve tips.
If you are having problems with the stout springs that normally come with the TFS heads then your cam ramp speed may be too high. You might try a little slower lobe, 3/8" pushrods (they drop right in with 1.7 rockers) or you might install some of the springs with less pressure like the "Gold" or "Platinum" and then shim them within .050" of coil bind. Shimming springs within .050” of coil bind takes the “surge” out of them. When the valve train reaches float, power tends to drop like a rock off a cliff, what you may be seeing is spring surge rather than float.
I hope this helps.
The problem with a stock GM 15 degree rocker (the 12 degree rocker is different) is that over .550" lift the rocker starts to scrub. This "scrub" can damage the valve tips and will cause wear to the bronze guides (powdered metal guides tend to last, but not always) We have seen this on EVERY type of 15 degree head made including AFR, Dart and even GM when bronze guides are installed (stock GM has powdered metal guides).
Most everyone understands how roller rocker geometry should work. As the trunion is raised, the sweep width is decreased, side loading is decreased, lift is increased and life is good. This is called "full arc" type geometry and is what most roller rocker manufacturers who know what they're doing strive for, like Jesel.
As you shim up a GM stock rocker you decrease the sweep pattern, but you INCREASE scrub and increase lift. The increase in lift is a good thing, and is part of the power gain you are seeing. You have to remember that a stock rocker GAINS ratio as it lifts the valve, unlike a roller rocker. As the stock rocker is shimmed up, it gains even more ratio.
The increase in scrub is a disaster waiting to happen. If you remember the problems AFR had when they had some soft valve tips and the valves would get worn down to the locks, this is the same thing you will see long term with shimming up stock rockers, on any head, including the TFS heads.
A stock GM rocker needs to work like a rocking chair works, or like a gear meshes, and is what the stock rocker does well up to about .550" lift, this is called "half arc" geometry. The sweep pattern looks wide, but is simply a function of how a stock rocker must operate. Everything past "half arc" results in the tip of the rocker arm DRAGGING itself across the top of the valve, not good for valve tips or guides.
If you look at WHERE the rocker scroll is contacting the valve at full lift (.600" or so) you will see it's on the VERY TIP END of the rocker scroll with a contact pattern about .010"-.020" wide. This narrow contact patch combined with maximum spring pressure at maximum lift puts the PSI (pounds per square inch) of the contact patch in the stratosphere. (FYI, an LS7 rocker at .650" lift has more contact patch than a LS1 rocker at .600")
Think about having a rocking chair on your wifes new hardwood floor, rock all the way forward to the very tip end of the rails, and then take your feet and push the chair backwards digging the tip of the rails into the floor. This is what a stock rocker does past about .550" or so, the more it's shimmed, the SOONER in the lift cycle this occurs.
The TFS heads come with springs that check at 160 seat 450 open. If you attempt to run stock rockers you need to install powdered metal guides to eliminate the guide wear, and install springs that are no more than 400 open, like the "platinum" springs that TEA sells, they check at 160 seat 400 open. This lesser open pressure makes life easier on the valve tips.
If you are having problems with the stout springs that normally come with the TFS heads then your cam ramp speed may be too high. You might try a little slower lobe, 3/8" pushrods (they drop right in with 1.7 rockers) or you might install some of the springs with less pressure like the "Gold" or "Platinum" and then shim them within .050" of coil bind. Shimming springs within .050” of coil bind takes the “surge” out of them. When the valve train reaches float, power tends to drop like a rock off a cliff, what you may be seeing is spring surge rather than float.
I hope this helps.
Last edited by Brian Tooley Racing; 09-17-2010 at 11:18 PM.
09-17-2010, 11:11 PM
#10
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Nice writeup Shane, but I would like to include some information that the average customer may not know or understand that is important to long term durability. If it's a race only application that isn't driven on the street, then disregard the information below. If it's driven on the street, then you need to understand this information.
The problem with a stock GM 15 degree rocker (the 12 degree rocker is different) is that over .550" lift the rocker starts to scrub. This "scrub" can damage the valve tips and will cause wear to the bronze guides (powdered metal guides tend to last, but not always) We have seen this on EVERY type of 15 degree head made including AFR, Dart and even GM when bronze guides are installed.
Most everyone understands how roller rocker geometry should work. As the trunion is raised, the sweep width is decreased, side loading is decreased, lift is increased and life is good. This is called "full arc" type geometry and is what most roller rocker manufacturers who know what they're doing strive for, like Jesel.
As you shim up a GM stock rocker you decrease the sweep pattern, but you INCREASE scrub and increase lift. The increase in lift is a good thing, and is part of the power gain you are seeing. You have to remember that a stock rocker GAINS ratio as it lifts the valve, unlike a roller rocker. As the stock rocker is shimmed up, it gains even more ratio.
The increase in scrub is a disaster waiting to happen. If you remember the problems AFR had when they had some soft valve tips and the valves would get worn down to the locks, this is the same thing you will see long term with shimming up stock rockers, on any head, including the TFS heads.
A stock GM rocker needs to work like a rocking chair works, or like a gear meshes, and is what the stock rocker does well up to about .550" lift, this is called "half arc" geometry. The sweep pattern looks wide, but is simply a function of how a stock rocker must operate. Everything past "half arc" results in the tip of the rocker arm DRAGGING itself across the top of the valve, not good for valve tips or guides.
If you look at WHERE the rocker scroll is contacting the valve at full lift you will see it's on the VERY TIP END of the rocker scroll with a contact pattern about .010"-.020" wide. This narrow contact patch combined with maximum spring pressure at maximum lift puts the PSI (pounds per square inch) of the contact patch in the stratosphere.
Think about having a rocking chair on your wifes new hardwood floor, rock all the way forward to the very tip end of the rails, and then take your feet and push the chair backwards digging the tip of the rails into the floor. This is what a stock rocker does, the more it's shimmed, the SOONER in the lift cycle this occurs.
The TFS heads come with springs that check at 160 seat 450 open. If you attempt to run stock rockers you need to install powdered metal guides to eliminate the guide wear, and install springs that are no more than 400 open, like the "platinum" springs that TEA sells, they check at 160 seat 400 open. This lesser open pressure makes life easier on the valve tips.
If you are having problems with the stout springs that normally come with the TFS heads then your cam ramp speed may be too high. You might try a little slower lobe, 3/8" pushrods (they drop right in with 1.7 rockers) or you might install some of the springs with less pressure like the "Gold" or "Platinum" and then shim them within .050" of coil bind. Shimming springs within .050” of coil bind takes the “surge” out of them. When the valve train reaches float, power tends to drop like a rock off a cliff, what you may be seeing is spring surge rather than float.
I hope this helps.
The problem with a stock GM 15 degree rocker (the 12 degree rocker is different) is that over .550" lift the rocker starts to scrub. This "scrub" can damage the valve tips and will cause wear to the bronze guides (powdered metal guides tend to last, but not always) We have seen this on EVERY type of 15 degree head made including AFR, Dart and even GM when bronze guides are installed.
Most everyone understands how roller rocker geometry should work. As the trunion is raised, the sweep width is decreased, side loading is decreased, lift is increased and life is good. This is called "full arc" type geometry and is what most roller rocker manufacturers who know what they're doing strive for, like Jesel.
As you shim up a GM stock rocker you decrease the sweep pattern, but you INCREASE scrub and increase lift. The increase in lift is a good thing, and is part of the power gain you are seeing. You have to remember that a stock rocker GAINS ratio as it lifts the valve, unlike a roller rocker. As the stock rocker is shimmed up, it gains even more ratio.
The increase in scrub is a disaster waiting to happen. If you remember the problems AFR had when they had some soft valve tips and the valves would get worn down to the locks, this is the same thing you will see long term with shimming up stock rockers, on any head, including the TFS heads.
A stock GM rocker needs to work like a rocking chair works, or like a gear meshes, and is what the stock rocker does well up to about .550" lift, this is called "half arc" geometry. The sweep pattern looks wide, but is simply a function of how a stock rocker must operate. Everything past "half arc" results in the tip of the rocker arm DRAGGING itself across the top of the valve, not good for valve tips or guides.
If you look at WHERE the rocker scroll is contacting the valve at full lift you will see it's on the VERY TIP END of the rocker scroll with a contact pattern about .010"-.020" wide. This narrow contact patch combined with maximum spring pressure at maximum lift puts the PSI (pounds per square inch) of the contact patch in the stratosphere.
Think about having a rocking chair on your wifes new hardwood floor, rock all the way forward to the very tip end of the rails, and then take your feet and push the chair backwards digging the tip of the rails into the floor. This is what a stock rocker does, the more it's shimmed, the SOONER in the lift cycle this occurs.
The TFS heads come with springs that check at 160 seat 450 open. If you attempt to run stock rockers you need to install powdered metal guides to eliminate the guide wear, and install springs that are no more than 400 open, like the "platinum" springs that TEA sells, they check at 160 seat 400 open. This lesser open pressure makes life easier on the valve tips.
If you are having problems with the stout springs that normally come with the TFS heads then your cam ramp speed may be too high. You might try a little slower lobe, 3/8" pushrods (they drop right in with 1.7 rockers) or you might install some of the springs with less pressure like the "Gold" or "Platinum" and then shim them within .050" of coil bind. Shimming springs within .050” of coil bind takes the “surge” out of them. When the valve train reaches float, power tends to drop like a rock off a cliff, what you may be seeing is spring surge rather than float.
I hope this helps.
And this is why I refuse to use stock rockers on my tea tfs heads... everyone can shout they are better from the mountain top... but I need a reliable setup.
09-18-2010, 10:56 AM
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Brian,
Of course you are correct in your explaination of the changes in geometry and rocker action due to the shimming of the factory fulcrum point. The point I am making here is a customer bought a heads, cam, and rocker arm package from a very reputable vendor here. The parts were installed correctly by a third party and the car was broght here for a dyno tune. When the car wouldn't rev past 5500 I knew what the culprit was and gave the customer his options. I agree that our setup would increase valve tip and guide wear slightly, but the damage resulting from the instability in his initial setup would have been catastrophic. I have seen many more cases of broken springs, cracked locks, and dropped valves due to incorrect valvetrain setup and excessive valve bounce than I've seen damage from the accelerated tip and guide wear.
In any combination that I put together for a customer, their intended useage and needs are always the priority. There are occassions where I will run a roller rocker setup on an LSx platform but as you pointed out, valvespring choice and setup are ultra critical. If I cut a custom cam for someone wanting to use a roller rocker setup, I will be VERY conservative on lobe choice.
I guess it all comes down to a choice and risk. An informed consumer is always the goal for me.
Thanks,
Shane
Of course you are correct in your explaination of the changes in geometry and rocker action due to the shimming of the factory fulcrum point. The point I am making here is a customer bought a heads, cam, and rocker arm package from a very reputable vendor here. The parts were installed correctly by a third party and the car was broght here for a dyno tune. When the car wouldn't rev past 5500 I knew what the culprit was and gave the customer his options. I agree that our setup would increase valve tip and guide wear slightly, but the damage resulting from the instability in his initial setup would have been catastrophic. I have seen many more cases of broken springs, cracked locks, and dropped valves due to incorrect valvetrain setup and excessive valve bounce than I've seen damage from the accelerated tip and guide wear.
In any combination that I put together for a customer, their intended useage and needs are always the priority. There are occassions where I will run a roller rocker setup on an LSx platform but as you pointed out, valvespring choice and setup are ultra critical. If I cut a custom cam for someone wanting to use a roller rocker setup, I will be VERY conservative on lobe choice.
I guess it all comes down to a choice and risk. An informed consumer is always the goal for me.
Thanks,
Shane
