Pushrod length questions - LS7 lifters
Pushrod length questions - LS7 lifters Hello, I hope I am not making a thread that has been beaten to death. I am newer to this forum and not familiar with the topics that have been gone over, over, and over again like I am on some other forums.
I have been doing more research while waiting on a few final bits that are holding up reassembly of my L33.
I am putting the engine back together with a few changes that will affect pushrod length. After reading more I realize I may not have chosen a correct length when considering what combo I was putting together.
Assuming OEM Length - 7.400
I am changing the following and my PR length was chosen based on these parts below:
-Custom Comp cam
-Manley Pro-Flo Stainless I/E valves (should be stock size)
-.030 Compressed HG's (requires -.021 shorter pushrod)
-Heads milled .005 (requires -.005 shorter pushrod)
And then I came across info I was previously unaware of on a part I am installing:
-LS7 Lifters (requires +.050 additional PR length from what I have read)
Factoring that new measurement in it seems 7.425 is more likely to be closer to what i need. Does this sound correct?
I have been doing more research while waiting on a few final bits that are holding up reassembly of my L33.
I am putting the engine back together with a few changes that will affect pushrod length. After reading more I realize I may not have chosen a correct length when considering what combo I was putting together.
Assuming OEM Length - 7.400
I am changing the following and my PR length was chosen based on these parts below:
-Custom Comp cam
-Manley Pro-Flo Stainless I/E valves (should be stock size)
-.030 Compressed HG's (requires -.021 shorter pushrod)
-Heads milled .005 (requires -.005 shorter pushrod)
And then I came across info I was previously unaware of on a part I am installing:
-LS7 Lifters (requires +.050 additional PR length from what I have read)
Factoring that new measurement in it seems 7.425 is more likely to be closer to what i need. Does this sound correct?
Measure. Buy the $20 Comp checker and measure. Takes about 5 minutes.
I would say 7.4" would be right - you need .025" longer because the base circle is smaller on the aftermarket cam, but you've subtracted that with the gasket and milling, putting you back at stock length.
The LS7 lifter is forgiving on the pushrod length, however. You have a bit of room with the preload. Anywhere from .050" to .100" will work with it.
I would say 7.4" would be right - you need .025" longer because the base circle is smaller on the aftermarket cam, but you've subtracted that with the gasket and milling, putting you back at stock length.
The LS7 lifter is forgiving on the pushrod length, however. You have a bit of room with the preload. Anywhere from .050" to .100" will work with it.
OK, I figured I might get that response.
Curious though, I thought I read somewhere that the base circle diameter only decreases if lift is greater than .600+? My max lift on the custom comp grind is on the intake, and it is .581. Would my base circle be smaller?
I ordered comp cams PR length checker tool 7702-1, and an extra LS7 lifter that I will turn into a solid lifter. I found a couple how-to's on using the two to measure and choose the appropriate length. I guess I will just save the 7.375 PR's for another build.
Curious though, I thought I read somewhere that the base circle diameter only decreases if lift is greater than .600+? My max lift on the custom comp grind is on the intake, and it is .581. Would my base circle be smaller?
I ordered comp cams PR length checker tool 7702-1, and an extra LS7 lifter that I will turn into a solid lifter. I found a couple how-to's on using the two to measure and choose the appropriate length. I guess I will just save the 7.375 PR's for another build.
You don't really need a solid lifter to check pushrod length. That's for PtV clearance.
A checker spring is all you need (and they are like $2) if you even need that. All you want to do is get it to 0 lash, so there is nothing actually compressing the lifter. So you could get by with the springs you intent to run. I've done it both ways and it doesn't matter.
Put the rocker on just holding your finger and spin the adjustable pushrod until all the slack is taken out of the rocker. That means no up and down motion anymore. You're at 0 lash. Some say to bolt down the rocker, but that's has some movement and preloads the system and gives you a short pushrod. Just finger tight is all you need.
Then take the adj pushrod out and count the number of turns back to 0. Half turns are important and are .025" length. Multiply the turns by .050" and add to the baseline 6.8" and that's your pushrod length at 0 lash. Add your preload to that. If LS7 lifters, aim for .075" additional length.
You can check the pushrod length by spinning it out the original 0 lash number and then an additional 3/4 turn to build the proper length. Then bolt down your rocker after tightening down to 0 lash (again, just finger tight with no movement). Set you torque wrench to 22ft/lbs and measure the rotations to get to 22ft/lbs. You should be close to a full turn and a half for the .075" preload number. If so, you're good to go.
Check an exhaust and intake on both cylinder heads if you don't want to check all 16.
A checker spring is all you need (and they are like $2) if you even need that. All you want to do is get it to 0 lash, so there is nothing actually compressing the lifter. So you could get by with the springs you intent to run. I've done it both ways and it doesn't matter.
Put the rocker on just holding your finger and spin the adjustable pushrod until all the slack is taken out of the rocker. That means no up and down motion anymore. You're at 0 lash. Some say to bolt down the rocker, but that's has some movement and preloads the system and gives you a short pushrod. Just finger tight is all you need.
Then take the adj pushrod out and count the number of turns back to 0. Half turns are important and are .025" length. Multiply the turns by .050" and add to the baseline 6.8" and that's your pushrod length at 0 lash. Add your preload to that. If LS7 lifters, aim for .075" additional length.
You can check the pushrod length by spinning it out the original 0 lash number and then an additional 3/4 turn to build the proper length. Then bolt down your rocker after tightening down to 0 lash (again, just finger tight with no movement). Set you torque wrench to 22ft/lbs and measure the rotations to get to 22ft/lbs. You should be close to a full turn and a half for the .075" preload number. If so, you're good to go.
Check an exhaust and intake on both cylinder heads if you don't want to check all 16.
Last edited by JakeFusion; Apr 28, 2014 at 12:53 PM.
