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

Prettty simple. Different base circle on the cam. No big deal,luckilly you checked.

So taking .021 off the head gasket and the different base circle of the cam knocking .100-.125 off the PR length seems normal?

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

Yea I really tried to go by the book on checking everything in the valvetrain. There are a lot of different methods out there but I found one over on ls1gto.com and the tech at COMP sent me one that were identical so I went by that.

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.

Morel lifters generally require about a .050 shorter pushrod on their own.

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.

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 wasn't real sure about the LSR lobe's aggressiveness. Comp has been in the business about as long as anyone and since they designed this cam for these heads I decided it would be worth it to try it out. Not to mention they are local to me. I've already been very impressed with the difference in power over the LS1. Most I've done so far is just a 4.5k run, and I have to admit when rolling into it the "pulling like a freight train" I had read about is definitely there. From a stop I had thought the Toyo's were hooking pretty well before, but a 3k car with this setup is going to need some serious tire. I know when it get some more miles and it gets turned a few more R's there is going to be some spinning at 50-60mph if not more. Looks like the old wagon wheels are going to be getting a set of Nittos. :D Anyway, going to drive it all this week so the oil change should be coming pretty quick, I need something that isn't going to thin out as much upon warming up. I'm thinking of first trying an 0w40 or 5w40 blend. And if that doesn't seem to do it I'll go with the Mobil 0w50.

it looks like you have about .025" lifter pre-load. I think you should have slightly more - I have read that it should be .030" to .080". this is your valvetrain noise imo.
Are you running short travel morel lifters?
Barrett

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.