what is the stock preload?
Originally Posted by joshp14
I called 4 places today to inquire about this...I will be running Lunati 72432 lifters, AFR heads milled .024 (cometic .040) and the F13 cam. Here is what I found out:
Thunder said .060-.070 w/Heads/Cam Cars and stock is .080-.090
Texas-Speed said .020 (they also recommended to use Lunati Specs)
Lunati said .030-.040
AFR said .100
I got ranges from .020 all the way up to .100. I think I'll go somewhere around .030-.050 based on the answers I received.
Thunder said .060-.070 w/Heads/Cam Cars and stock is .080-.090
Texas-Speed said .020 (they also recommended to use Lunati Specs)
Lunati said .030-.040
AFR said .100
I got ranges from .020 all the way up to .100. I think I'll go somewhere around .030-.050 based on the answers I received.
Id do exactly what you have planned.... 
Thread Starter
Joined: Mar 2003
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From: North Carolina
Originally Posted by cantdrv65
LOL..... Like I said, if it was SO DAMN critical why do we have experts all over the board? Id do exactly what you have planned....
Id do exactly what you have planned....
Originally Posted by WS6FirebirdTA00
if you notice the guys that make great power and torque are the guys with motors properly setup.
Thats just it there is a WIDE variety of what the experts consider properly setup. Sounds like personal preference to me. Id go with the lifter manufacture Lunati.....
Last edited by cantdrv65; Mar 9, 2006 at 07:24 PM.
Thread Starter
Joined: Mar 2003
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From: North Carolina
i dont agree with that, i am talking guys like me who drive street cars taht make great power. now mine is nothing impressive yet but hopefully soon will be. ive seen a lot of disappointing power and torque numbers with setup that should outdo mine.
Originally Posted by BriancWS6
Take the base circle of the stock cam, the base circle of the new one, and subtract. Let's say that the base circle is .100 smaller. That means the radius is .050 less, which equals that much less preload. So if the "actual" length of the stock pushrods measure out to be 7.400 and the new ones measured out to an actual 7.450, then your preload will stay the same. This is what I plan to do when I get my cam. I am also gonna use the paint on the valve stem to verify that the pushrod length is correct. You want the paint to be removed off the center of the stem. Too high or too low would mean either too short or too long of a pushrod.
Here we go again. This topic comes up more times than I can count. The swipe of the valve stem isn't adjusted by the pushrod length but by shimming or cutting the rocker pedestals. Might want to do a little more research before you waste a lot of time chasing a never ending pushrod length. Think about it, just for an example it takes a .050" shorter pushrod to fix the swipe on the valve stem, then that means you have .050" less lifter preload because of the shorter pushrods. What are you are you going to do fix that? Install .050" longer pushrods? Ooops, your swipe just got screwed up again. See, it makes no sense.
Originally Posted by BriancWS6
Take the base circle of the stock cam, the base circle of the new one, and subtract. Let's say that the base circle is .100 smaller. That means the radius is .050 less, which equals that much less preload. So if the "actual" length of the stock pushrods measure out to be 7.400 and the new ones measured out to an actual 7.450, then your preload will stay the same. This is what I plan to do when I get my cam. I am also gonna use the paint on the valve stem to verify that the pushrod length is correct. You want the paint to be removed off the center of the stem. Too high or too low would mean either too short or too long of a pushrod.
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Joined: Mar 2003
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From: North Carolina
Originally Posted by GuitsBoy
Dont forget that the aftermarket 7.400 PRs are actually .020 longer than stock.
Originally Posted by WS6FirebirdTA00
what is the deal wtih that? so stock is 7.380? hmm, always thought they were 7.4
.020 longer than stock.
That being said, in stock headed applications, many vendors suggest you leave the .030 less preload there to help combat lifter pumpup at higher rpms, although im not sure now the extra preload supposedly helps this.
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Originally Posted by GuitsBoy
That being said, in stock headed applications, many vendors suggest you leave the .030 less preload there to help combat lifter pumpup at higher rpms, although im not sure now the extra preload supposedly helps this.
Originally Posted by HavATampa
Here we go again. This topic comes up more times than I can count. The swipe of the valve stem isn't adjusted by the pushrod length but by shimming or cutting the rocker pedestals. Might want to do a little more research before you waste a lot of time chasing a never ending pushrod length. Think about it, just for an example it takes a .050" shorter pushrod to fix the swipe on the valve stem, then that means you have .050" less lifter preload because of the shorter pushrods. What are you are you going to do fix that? Install .050" longer pushrods? Ooops, your swipe just got screwed up again. See, it makes no sense.
Originally Posted by GuitsBoy
Dont forget that the aftermarket 7.400 PRs are actually .020 longer than stock.
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From: BFE
Originally Posted by BriancWS6
So does this go for ALL pushrod engines? Or just ones using hydraulic lifters. I have read about this method before, and some old school engine builders use it as well. So enlighten me here.
This is specific to non adjustable rocker systems with stands (LSx in our case)
Stud systems adjust both geometry AND preload via p-rod length (like Comp Magnums)
That's why I said if the length was "actually" what they are suppose to be.
There is a .00x variance amongst a set in every motor.
Now a parameter rarely thought of is the measuring device and that can account for some reading variances besides actual ones.
Originally Posted by cantdrv65
At higher rpms when the valvetrain has lots of acceleration in will compress the plunger deeper into the lifter (pushes out more oil). Thats why a little less is better then a little too much. This is how Rhoads lifters work.
Originally Posted by PREDATOR-Z
Now a parameter rarely thought of is the measuring device and that can account for some reading variances besides actual ones.
I've only measured preload on one completely stock LS1 in a 1998 C5 vette.
I did it three times and each time got a measurement of .150"
I was very surprised it was so much, but the engine was running fine like that.
Personally I wonder why so many people remain stuck in the world of non-adjustable rockers when it is so easy to convert over to adjustables & guide-plates. That way you can easily get swipe and preload correct by simply using the right length pushrods.
I did it three times and each time got a measurement of .150"
I was very surprised it was so much, but the engine was running fine like that.
Personally I wonder why so many people remain stuck in the world of non-adjustable rockers when it is so easy to convert over to adjustables & guide-plates. That way you can easily get swipe and preload correct by simply using the right length pushrods.
Originally Posted by white2001s10
I've only measured preload on one completely stock LS1 in a 1998 C5 vette.
I did it three times and each time got a measurement of .150"
I was very surprised it was so much, but the engine was running fine like that.
Personally I wonder why so many people remain stuck in the world of non-adjustable rockers when it is so easy to convert over to adjustables & guide-plates. That way you can easily get swipe and preload correct by simply using the right length pushrods.
I did it three times and each time got a measurement of .150"
I was very surprised it was so much, but the engine was running fine like that.
Personally I wonder why so many people remain stuck in the world of non-adjustable rockers when it is so easy to convert over to adjustables & guide-plates. That way you can easily get swipe and preload correct by simply using the right length pushrods.
1. "dial indicator" measured preload = 0.163"
2. scribe pushrod loaded/unloaded and measure with calipers preload = 0.160" (as best I could eyeball)
im a bit confused. Can someone please explain exactly how to measure preload? Stock motor, f13 112, ls2/6 heads and stock rockers..right now im using 7.4" PR's. Measuring this is about at bad as all the different ways to measure a pinion angle 
Originally Posted by ninobrn99
im a bit confused. Can someone please explain exactly how to measure preload? Stock motor, f13 112, ls2/6 heads and stock rockers..right now im using 7.4" PR's. Measuring this is about at bad as all the different ways to measure a pinion angle
...They say to use a standard PR and set it to 0 lash on the lobe heel. Then to scribe it. Then torque the rocker down and wait 5 minutes for it to bleed and scribe it again. Then take it out and measure the distance between the marks.
Originally Posted by GuitsBoy
Lifter pump-up is actually the opposite. What youre describing is lifter bleed-down. Bleed down usually happens at lower rpms. Pump up happens at high rpms. Mu understanding of pumpup is that when all the inertia of the valvetrain parts gets ramped over the nose of the cam, there is a brief momen of near "weightlessness". (if it ever gets completely to weightlessness you get valve float.) During that time there is reduced spring pressure applied to the lifter. The lifter can actually be filled with too much oil as the high oil pressure can actually overpower the little bit of spring tension left. Now after the cam rotated down the rest of the closing ramp and spring pressure resumes, the lifter is already filled with just a little bit too much oil, which of course will not compress, nor will it bleed down fast enough, and thus the valve is held open by a few thousandths and bleeding off compression.
Thats my take on it anyway.
"This is why you can set preload to a variety of values and never see a difference in power."
The internet is great for opinions. Most opinions I've read on this site say it CAN affect power.
Not knocking what your saying, just pointing out the opinion is on both sides of the fence.
But if too much preload can hang valves open ( to the point the car won't start and it backfires through the intake ) then wouldn't it make sense that a little less than that ( enough for the car to run ) would be down on power too?
The internet is great for opinions. Most opinions I've read on this site say it CAN affect power.
Not knocking what your saying, just pointing out the opinion is on both sides of the fence.
But if too much preload can hang valves open ( to the point the car won't start and it backfires through the intake ) then wouldn't it make sense that a little less than that ( enough for the car to run ) would be down on power too?