81' malibu classic LQ4,80mm turbo build
02-09-2016, 05:49 PM
#27
I will add that by utilizing 1.8 ratio roller rockers in lieu of stock rocker arms with a trunion upgrade, that you'll have to pay a lot more attention to setting up the valve train to ensure valve float or valve train instability doesn't occur.
Most would think that by utilizing a LS9 camshaft that it would negate any issues with valve control, but roller rockers really can ruin the "party" so to speak very quickly. I would run at least 165-170# seated spring pressure and 425-430# open spring pressure to ensure adequate valve control at higher engine speeds. A PAC 1204X shimmed to the right installed height could be tasked to handle valve spring duties appropriately.
Going to a larger diameter 3/8" push rod would also be a good idea due to the added mass that must be accelerated through the initial portion of the lift curve when utilizing a roller rocker. This added mass can cause push rod deflection and when the push rod straightens back out it can cause separation in the valve train (lash). This allows the lifters to pump up momentarily and when the separation (lash) is taken out of the valve train the lifter will still stay pumped up briefly, acting like a solid lifter. This will hang the valve open and allow trapped cylinder pressure to escape resulting in loss of power and/or power to completely tank and fall off.
So, stiff push rods and higher spring pressures are the key to taming and controlling the added mass the roller rockers add to the valve train.
Hope this helps!
Most would think that by utilizing a LS9 camshaft that it would negate any issues with valve control, but roller rockers really can ruin the "party" so to speak very quickly. I would run at least 165-170# seated spring pressure and 425-430# open spring pressure to ensure adequate valve control at higher engine speeds. A PAC 1204X shimmed to the right installed height could be tasked to handle valve spring duties appropriately.
Going to a larger diameter 3/8" push rod would also be a good idea due to the added mass that must be accelerated through the initial portion of the lift curve when utilizing a roller rocker. This added mass can cause push rod deflection and when the push rod straightens back out it can cause separation in the valve train (lash). This allows the lifters to pump up momentarily and when the separation (lash) is taken out of the valve train the lifter will still stay pumped up briefly, acting like a solid lifter. This will hang the valve open and allow trapped cylinder pressure to escape resulting in loss of power and/or power to completely tank and fall off.
So, stiff push rods and higher spring pressures are the key to taming and controlling the added mass the roller rockers add to the valve train.
Hope this helps!
02-10-2016, 01:48 PM
#29
I will add that by utilizing 1.8 ratio roller rockers in lieu of stock rocker arms with a trunion upgrade, that you'll have to pay a lot more attention to setting up the valve train to ensure valve float or valve train instability doesn't occur.
Most would think that by utilizing a LS9 camshaft that it would negate any issues with valve control, but roller rockers really can ruin the "party" so to speak very quickly. I would run at least 165-170# seated spring pressure and 425-430# open spring pressure to ensure adequate valve control at higher engine speeds. A PAC 1204X shimmed to the right installed height could be tasked to handle valve spring duties appropriately.
Going to a larger diameter 3/8" push rod would also be a good idea due to the added mass that must be accelerated through the initial portion of the lift curve when utilizing a roller rocker. This added mass can cause push rod deflection and when the push rod straightens back out it can cause separation in the valve train (lash). This allows the lifters to pump up momentarily and when the separation (lash) is taken out of the valve train the lifter will still stay pumped up briefly, acting like a solid lifter. This will hang the valve open and allow trapped cylinder pressure to escape resulting in loss of power and/or power to completely tank and fall off.
So, stiff push rods and higher spring pressures are the key to taming and controlling the added mass the roller rockers add to the valve train.
Hope this helps!
Most would think that by utilizing a LS9 camshaft that it would negate any issues with valve control, but roller rockers really can ruin the "party" so to speak very quickly. I would run at least 165-170# seated spring pressure and 425-430# open spring pressure to ensure adequate valve control at higher engine speeds. A PAC 1204X shimmed to the right installed height could be tasked to handle valve spring duties appropriately.
Going to a larger diameter 3/8" push rod would also be a good idea due to the added mass that must be accelerated through the initial portion of the lift curve when utilizing a roller rocker. This added mass can cause push rod deflection and when the push rod straightens back out it can cause separation in the valve train (lash). This allows the lifters to pump up momentarily and when the separation (lash) is taken out of the valve train the lifter will still stay pumped up briefly, acting like a solid lifter. This will hang the valve open and allow trapped cylinder pressure to escape resulting in loss of power and/or power to completely tank and fall off.
So, stiff push rods and higher spring pressures are the key to taming and controlling the added mass the roller rockers add to the valve train.
Hope this helps!
02-10-2016, 02:56 PM
#30
I see a lot of guys that pounce on roller rockers because they find them for good deals, but not fully realizing that rocker arm will require them to spend more money on valve train components to ensure that they don't run into valve control issues.
I would highly recommend 3/8" push rods in lieu of the 5/16" push rods that you have for added rigidity and for resistance against deflection.
In my experience, LS7 lifters have caused issues when used in conjunction with roller rockers. I've seen people gain a lot of missing power and added RPM when they switched from a LS7 lifter to a short travel style link bar lifter. The LS7 lifter has too much internal travel and when they're run at the preload recommendations most suggest causes the lifter to pump up excessively hanging the valve open even further. This results in large losses in power and power falls off prematurely.
Honestly if I were you, I'd shelve the roller rockers and run a stock rocker with a trunion upgrade. You can keep your 5/16" push rods and LS7 lifters and have a nice running combination. Of course you could always run the roller rockers with 5/16" push rods and LS7 lifters, but IMO it will not be optimal and possibly cause issues with valve control from my experiences.
Most people run .060-.080" preload with LS7 lifters. Some run .100" or more, and some run less than .060" all the way down to .020" preload. Running more preload has its own benefits just as running less preload has its benefits. At the same time there are also cons to running more preload and cons to running less preload.
I would highly recommend 3/8" push rods in lieu of the 5/16" push rods that you have for added rigidity and for resistance against deflection.
In my experience, LS7 lifters have caused issues when used in conjunction with roller rockers. I've seen people gain a lot of missing power and added RPM when they switched from a LS7 lifter to a short travel style link bar lifter. The LS7 lifter has too much internal travel and when they're run at the preload recommendations most suggest causes the lifter to pump up excessively hanging the valve open even further. This results in large losses in power and power falls off prematurely.
Honestly if I were you, I'd shelve the roller rockers and run a stock rocker with a trunion upgrade. You can keep your 5/16" push rods and LS7 lifters and have a nice running combination. Of course you could always run the roller rockers with 5/16" push rods and LS7 lifters, but IMO it will not be optimal and possibly cause issues with valve control from my experiences.
Most people run .060-.080" preload with LS7 lifters. Some run .100" or more, and some run less than .060" all the way down to .020" preload. Running more preload has its own benefits just as running less preload has its benefits. At the same time there are also cons to running more preload and cons to running less preload.