Pushrod length for LS3 heads on LQ9 block
02-07-2012, 09:17 AM
#1
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Pushrod length for LS3 heads on LQ9 block yeah, I know, measure. I did, but my measured values don't jive with what I expected, hence this post.
My motor has bone stock LS3 heads, with GM LS3 head gaskets, mounted to an LQ9 block at standard deck height. The cam is a 227/231 Comp grind.
Most of my reading indicates that cams with above a 224 duration are ground on a .060" smaller base circle, which would indicate that the "right" pushrod length would be 7.430 as opposed to the stock 7.4. However, my measurements indicate that I need a 7.35" pushrod in order to have ~.050" preload. I expected to need a longer than stock pushrod, not shorter. I measured all 16, with a low measured at 7.3" at zero preload, a high measured at 7.3125, with most right in the middle at 7.30625. Add .050 preload to that, you get 7.35625, which tells me I need 7.35" pushrods.
But again, does it make sense? I expected to need something longer than 7.4, not smaller.
My motor has bone stock LS3 heads, with GM LS3 head gaskets, mounted to an LQ9 block at standard deck height. The cam is a 227/231 Comp grind.
Most of my reading indicates that cams with above a 224 duration are ground on a .060" smaller base circle, which would indicate that the "right" pushrod length would be 7.430 as opposed to the stock 7.4. However, my measurements indicate that I need a 7.35" pushrod in order to have ~.050" preload. I expected to need a longer than stock pushrod, not shorter. I measured all 16, with a low measured at 7.3" at zero preload, a high measured at 7.3125, with most right in the middle at 7.30625. Add .050 preload to that, you get 7.35625, which tells me I need 7.35" pushrods.
But again, does it make sense? I expected to need something longer than 7.4, not smaller.
02-10-2012, 10:50 AM
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most likely coming from the lifter difference, and possibly the LS3 valve tip height could be different.
Whatever it is, it is LOL
I just put 7.300 in a motor with LS3 heads milled .025, and Lunati link bar lifters, and set it at .035 preload. I haven't used that short of one before that I can recollect. Measured it several times and kept getting 7.265 "0" lash
Whatever it is, it is LOL
I just put 7.300 in a motor with LS3 heads milled .025, and Lunati link bar lifters, and set it at .035 preload. I haven't used that short of one before that I can recollect. Measured it several times and kept getting 7.265 "0" lash
02-10-2012, 01:09 PM
#4
Isnt' this the whole point of measuring? You're talking about a 0.005in difference from stock. That seems reasonable considering the stackup of tolerances from the cam to cam bearings to cam bores to deck height to gasket thickness to cylinder head datums to rocker installed position including valve stem installed height, rocker stand location, dowel pin locations, lifter height, etc. There are a lot of dimensions to stack up that could result in a range of PR lengths.
What method did you use to measure and determine preload?
What method did you use to measure and determine preload?
02-12-2012, 03:04 PM
#6
You might also try this method:
https://ls1tech.com/forums/15796641-post9.html
https://ls1tech.com/forums/15796641-post9.html
So when do you plan on installing the TSP VVT-2 cam?
02-20-2012, 12:12 PM
#7
Don't thank me - thank the guy that posted that method. Looks reasonable to me!
I think I'll stab the cam in during the next engine test fit. I want the engine in the car rather than on the stand when I torque that phaser bolt. I can see the engine stand flipping over and I just think it's better supported in the car. The engine will come back out again afterwards and I'll seal the timing cover and oil pan at that time. Still not sure if I'm going to pull the heads to check P-V clearance, but speaking of helpful links, here is some good info on locking the phaser for that process: https://ls1tech.com/forums/generatio...g-vvt-cam.html
I think I'll stab the cam in during the next engine test fit. I want the engine in the car rather than on the stand when I torque that phaser bolt. I can see the engine stand flipping over and I just think it's better supported in the car. The engine will come back out again afterwards and I'll seal the timing cover and oil pan at that time. Still not sure if I'm going to pull the heads to check P-V clearance, but speaking of helpful links, here is some good info on locking the phaser for that process: https://ls1tech.com/forums/generatio...g-vvt-cam.html
