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Does pushrod length affect lift?

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Old Jul 2, 2012 | 10:30 PM
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Default Does pushrod length affect lift?

Ok this is a stupid question lol, but I can't get it out of my head. I remember reading somewhere that if you don't put long enuf pushrods in when you put in a cam with a smaller base circle you don't see the full lift of the cam... This doesn't make sense to me thought because you have to torque your nut down either way so to me there should be now way the length affects full lift?
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Old Jul 3, 2012 | 12:11 AM
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If you run too short of a pushrod, to the point you have no preload on the lifter, it can give you less lift. Same goes for too long. You will bottom out the plunger and the valves will hang open.

Too long or too short, You will have other problems before you notice the effects of the variation in lift.
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Old Jul 3, 2012 | 12:14 AM
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Originally Posted by bww3588
If you run too short of a pushrod, to the point you have no preload on the lifter, it can give you less lift. Same goes for too long. You will bottom out the plunger and the valves will hang open.

Too long or too short, You will have other problems before you notice the effects of the variation in lift.
but .050 shorter should not cause those problems right?
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Old Jul 3, 2012 | 01:09 AM
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It will. Stock lifters typically run .060 to .080 preload. If you take .050 off that, your looking at .010 to .030 preload. It's going to make so much noise you won't want to drive it.
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Old Jul 3, 2012 | 01:19 AM
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Yea but if you still torque down to 22 ft lbs you should have the same preload?
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Old Jul 3, 2012 | 01:28 AM
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No, pushrod length determines preload. Not rocker arm torque.
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Old Jul 3, 2012 | 01:33 AM
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Originally Posted by bww3588
No, pushrod length determines preload. Not rocker arm torque.
I would think they both determine preload? If you didn't put any torque on it there would be zero preload. So if you torqued to 24 ft lbs you would be closer to stock preload again. Not at all saying this is the right way to do it, but sounds like it might work to me
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Old Jul 3, 2012 | 07:13 AM
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Originally Posted by bww3588
It will. Stock lifters typically run .060 to .080 preload. If you take .050 off that, your looking at .010 to .030 preload. It's going to make so much noise you won't want to drive it.
i can tell you this isn't completely true. i was running .060 on ls7 lifters and had some sewing machine sound. i'm now running right at .030 on the same lifters and my valvetrain is dead silent

Originally Posted by sweet99ss
I would think they both determine preload? If you didn't put any torque on it there would be zero preload. So if you torqued to 24 ft lbs you would be closer to stock preload again. Not at all saying this is the right way to do it, but sounds like it might work to me
not true either. think of it this way. once the rocker makes full contact with the stand you are no longer moving the pr. at this point you are only stretching the bolt. so if you put 10lbs or 50lbs of torque on it the pr is in the same place.


as for your original question having a pr that is shorter than the distance from the cup of the lifter to the cup of the rocker will reduce lift. it will also be VERY loud and chew up parts quickly. having a pr that is way too long to the point it bottoms out the lifter will move the valve off the seat before the cam lobe even moves the lifter. this is adding lift to the valve but it will be very obvious if this is the case. due to the valves being open when they shouldn't be it won't run very well(if at all) and won't make power either.
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Old Jul 3, 2012 | 08:05 AM
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You are right. I am aware that running looser preload will quiet it down, but for argument sake, I left that out to keep from confusing the thread.

However, generally speaking, it is not good to run such low preload as it can cause more problems than it is worth.
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Old Jul 3, 2012 | 08:09 AM
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What problems come with running lighter preload? I'm not being a dick, I'm just curious
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Old Jul 3, 2012 | 09:07 AM
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A side effect can induce valve float.
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Old Jul 3, 2012 | 09:28 AM
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Originally Posted by PREDATOR-Z
A side effect can induce valve float.
I did not know that. I'm running hollow/sodium valves, 3/8 pr's, and the correct spring pressure so hopefully I'll be ok. My graph was clean so I think I'm good. What about the lighter preload makes it more prone to valve float?
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Old Jul 3, 2012 | 10:14 AM
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So i should not run stockers with a hot cam?
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Old Jul 3, 2012 | 10:18 AM
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stock lifters are ok for most cams. stock pushrods are not.
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Old Jul 3, 2012 | 10:35 AM
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Pushrods can change lift in a stud mount rocker system. In a pedestal mount system, like LS1 and SBF, see above.
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Old Jul 3, 2012 | 02:08 PM
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Ok so i shuld or should not run stock pushrods with the hot cam? I know they will fbe fine as far as strength goes, but is the length going to be ok? Idk how much smaller base cir le on the cam is?

Main question here is will stockers work with the hot cam?
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Old Jul 3, 2012 | 02:24 PM
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Originally Posted by sweet99ss
Ok so i shuld or should not run stock pushrods with the hot cam? I know they will fbe fine as far as strength goes, but is the length going to be ok? Idk how much smaller base cir le on the cam is?

Main question here is will stockers work with the hot cam?
Best thing is to measure, but if you can find the recommended length it might not be required.

I would be more worried about the quality. The stock pushrods are not good and I would bet if you roll yours across a perfectly flat surface you find at least 1 that is already bent.
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