PR Length doesn't seem to measure right?
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PR Length doesn't seem to measure right?
Swapped a LS3 headed LQ block into my C5. Went with the Comp 273 LSR cam and .030 Cometics. After installing the cam I proceeded to check PR length on it instead of just throwing 7.4's back in. Following events turned into a headache. I took some old lifters and made them solid, not knowing how much exactly the LS7's would pump up I wanted to be sure that I would know they would never be able to go any higher than what I could replicate, so there would be no worry of different PTV tolerances after the engine was running. Just by estimating, I was shooting for having a .021 difference in what I would need since the block had never been decked and neither had the heads. I knew base circle size could be a factor though. After finding the base circle and adjusting the pushrod to the right length at zero lash I came out with a 7.2750 length. I checked atleast 10 times and was puzzled at why I would need a PR this short when all that had been changed was a headgasket and cam. I proceeded to just try and put the factory 7.4's back in to see what kind of issue it would make. When snugging down the rocker bolt I observed the valve opening about .100 which is about the difference it showed to be after preload. I ended up getting some 7.3 COMP mags and installing them. After firing up the new motor I am more worried about the situation enough to post for some advice. The engine has significant valvetrain noise, which I know is almost always an issue when the factory valvetrain is modified. But being my first cammed LS I have heard in person, I don't honestly know if it's just the same old noise or that the PR could possibly be too short. Another thought that crossed my mind was that I know all LS use 7.4 PR but could interchanging blocks/heads make a difference?
-Bo
-Bo
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My LS3 combo needed 7.300 pushrods. WCCH heads milled .030, LS7 gasket, custom cam, and morell lifters. It's important to always check the preload when you change anything in the valve train.
You can try different oil to help quite the valvetrain. The old LS1 liked Castrol Syntec 0W-30, but it always had that sewing machine sound to some degree. Probably in the cam profile. Larger cam in the LS3 is nice and quite.
Good thing you checked the preload
DJ
You can try different oil to help quite the valvetrain. The old LS1 liked Castrol Syntec 0W-30, but it always had that sewing machine sound to some degree. Probably in the cam profile. Larger cam in the LS3 is nice and quite.
Good thing you checked the preload
DJ
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My LS3 combo needed 7.300 pushrods. WCCH heads milled .030, LS7 gasket, custom cam, and morell lifters. It's important to always check the preload when you change anything in the valve train.
You can try different oil to help quite the valvetrain. The old LS1 liked Castrol Syntec 0W-30, but it always had that sewing machine sound to some degree. Probably in the cam profile. Larger cam in the LS3 is nice and quite.
Good thing you checked the preload
DJ
You can try different oil to help quite the valvetrain. The old LS1 liked Castrol Syntec 0W-30, but it always had that sewing machine sound to some degree. Probably in the cam profile. Larger cam in the LS3 is nice and quite.
Good thing you checked the preload
DJ
That makes me feel better, as LS7 HG's are .051 compressed correct? You have around .010 difference than me then. I think I might have went a little overboard trying to keep the lifters solid as I really am not sure how much the LS7's pump up but I'm going to run a 160 or 180 stat and a little thicker oil than the 5-30, as my oil pressure isn't where I'd like it after the oil reaches 190* or so. Maybe that will quiet it some upon getting to operating temp.
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Well that kind of puts me back where I was then, seems like they should have been around 7.350. I'm going to try the different oil in around another 500 miles after the break in process. After that I'll report back.
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What you are hearing is most likely the sewing machine sound of the LSR lobes.... They are pretty aggressive lobes, not the most but are pretty hot.... Those lobes cause some substanial valvtrain noise.....
I chuckled when I read your post, don't be scurd of it hauz......
When you punch it and go sideways on a 70 MPH freeway with cars on the road, thats a time when you need to be scurd.....lol then and only then will you truly respect the power......
Bozz
I chuckled when I read your post, don't be scurd of it hauz......
When you punch it and go sideways on a 70 MPH freeway with cars on the road, thats a time when you need to be scurd.....lol then and only then will you truly respect the power......
Bozz
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What you are hearing is most likely the sewing machine sound of the LSR lobes.... They are pretty aggressive lobes, not the most but are pretty hot.... Those lobes cause some substanial valvtrain noise.....
I chuckled when I read your post, don't be scurd of it hauz......
When you punch it and go sideways on a 70 MPH freeway with cars on the road, thats a time when you need to be scurd.....lol then and only then will you truly respect the power......
Bozz
I chuckled when I read your post, don't be scurd of it hauz......
When you punch it and go sideways on a 70 MPH freeway with cars on the road, thats a time when you need to be scurd.....lol then and only then will you truly respect the power......
Bozz
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sorry for the bump.
using this page as a bookmark for when i measure my pushrods. i went from ls7 lifters to morel 5206 and had my heads milled .015" when i take the slack out of the rocker arm i get just over 2 turns be for the bolt stops.
using this page as a bookmark for when i measure my pushrods. i went from ls7 lifters to morel 5206 and had my heads milled .015" when i take the slack out of the rocker arm i get just over 2 turns be for the bolt stops.