Base circle and pushrod length issues with high lift cams?
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Teching In
Joined: Feb 2002
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Base circle and pushrod length issues with high lift cams? Okay, most are aware that the '02 Z06 cam uses longer valves to compensate for the reduced base circle diameter neccessary to get the high lift. And everyone seems afraid to run this cam in an LS1 for this reason. So why is nobody afraid of the high lift aftermarket cams for the same reason? I have not heard of anybody compensating for smaller base circles in aftermarket cams with different length pushrods or anything. Or even bothering to check if it's neccessary, seems everyone just assumes it must be okay since the cam vendors haven't come out and said anything about it. And yes, the aftermarket cams do use smaller base circles, it's the only way to physically make the cam fit in the bore. I verified this with Comp Cams tech support.
Probably more than just a coincidence that the '01 Z06 and Hotcam both have the same lift (.525"). Maybe because GM knows that higher lift may cause problems unless something is done to compensate, as in the longer valves in the '02 LS6? So I'm wondering how much danger there is in terms of long term reliability and valvetrain wear with lifts above .525" unless you somehow compensate for the change in base circle? I've searched all the threads I could find on cams, and have not yet seen this discussed. Any thoughts/opinions? I haven't heard of any major issues yet from people running a high lift cam, but I wonder if this is something that will show up as an issue after 30 or 40k miles? I want to order a cam soon, but right now am afraid to go over .525" lift until I know I won't be causing any problems.
Probably more than just a coincidence that the '01 Z06 and Hotcam both have the same lift (.525"). Maybe because GM knows that higher lift may cause problems unless something is done to compensate, as in the longer valves in the '02 LS6? So I'm wondering how much danger there is in terms of long term reliability and valvetrain wear with lifts above .525" unless you somehow compensate for the change in base circle? I've searched all the threads I could find on cams, and have not yet seen this discussed. Any thoughts/opinions? I haven't heard of any major issues yet from people running a high lift cam, but I wonder if this is something that will show up as an issue after 30 or 40k miles? I want to order a cam soon, but right now am afraid to go over .525" lift until I know I won't be causing any problems.
TECH Junkie
Joined: Nov 2001
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From: Los Angeles
Re: Base circle and pushrod length issues with high lift cams? The lifters have a lot of slop in them and most cams fit within the range.
However, when I change cams (which is too many times to count these days) I measure the basecircle. Recently I swapped from a cam with 530'ish lift to a 565'ish lift, and it was just enough where I had to go to longer pushrods (had 7.350's and now I have 7.400's). I ran very little preload on my previous cam so thats why the little bit was enough to push me over the edge.
Now, MOST people dont need to check this because they run a large amount of lifter preload (maybe 70-80 thousanths?) stock and when they put the other cam in the basecircle maybe shrinks 30-50 thou still gives them enough lifter preload...thus its A-ok.
In other words, I'd assume that cam will work with stock pushrods just fine....
However, when I change cams (which is too many times to count these days) I measure the basecircle. Recently I swapped from a cam with 530'ish lift to a 565'ish lift, and it was just enough where I had to go to longer pushrods (had 7.350's and now I have 7.400's). I ran very little preload on my previous cam so thats why the little bit was enough to push me over the edge.
Now, MOST people dont need to check this because they run a large amount of lifter preload (maybe 70-80 thousanths?) stock and when they put the other cam in the basecircle maybe shrinks 30-50 thou still gives them enough lifter preload...thus its A-ok.
In other words, I'd assume that cam will work with stock pushrods just fine....
Thread Starter
Teching In
Joined: Feb 2002
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Re: Base circle and pushrod length issues with high lift cams? jmx- thanks for the info. Your the first person I've heard of ever measuring this stuff and using a non-stock length pushrod in an LS1. Maybe others do and just don't mention it, dunno. How did you determine the lifter preload? I'd like to know what/how to measure when I do my cam swap to make sure everything is right. Too bad the cam companies don't publish base circle diameter, make it real easy to determine what pushrod length to use, all else being stock. I'll probably stay under .540" lift, guess this is okay with stock length pushrods? Still makes me uneasy when GM lengthens the valves to go over .525" though.
