03 BLACKOUTSSS

iTrader: (3)

Anyone know where I can find this info...searching yielded a lot of good info, just not this one little piece. If I can get this, I can mathematically figure out the proper PR length based on the amount of preload desired.

Any Ideas?

03 BLACKOUTSSS

iTrader: (3)

no ideas huh?

Anyone think calling the dealership will get me anywhere?

shandy294

IDK,I thought you'd have gotten some replies.

budhayes3

iTrader: (19)

You could try calling the dealership, but I don't think that you'll get a straight answer. Maybe try PM'ing Zippy, he worked for a Chevy dealer for a long time, and is probably your best shot. If you have problems getting in touch with him here, try over at SilveradoSS.com, he's and admin there and on that site pretty much every day...

If you find out, post up your findings...now I'm curious to know myself

ricoc

Comp Cams say .030"

or you can just take a chance that someone on the internet said it was OK to just use the same length pushrods as they did

budhayes3

iTrader: (19)

Hmmm...is that Comp's spec or the factory spec? That seems to be on the loose side of acceptable clearance.

From the research that 03 BLACKOUTSSS has been doing, I'm sure that he's attempting to do it the right way and not the "internet said so" route lol.

ricoc

that number is what I "remember" from doing my cam last year.
After squishing the lifter .030" from zero lash, my push rods had to be .070" shorter than stock. I assume my valves are worn that much. Still no bad sounds from the drive train. Pity GM didn't use adjustable rockers.

03 BLACKOUTSSS

iTrader: (3)

Here are the factors that I can come up with for calculating the factory preload with an aftermarket setup...

Assuming the factory PRs are 7.380"

Factory PR preload - Zippy got back to me and said it was .050" - .090"
With that said, I am shooting for .070" preload

Variance in compressed Head Gasket Thickness - I have been told that the stock gaskets are .051" - .053". I installed a .041" gasket, which is a variance of .010" - .012", assuming .011" head gasket change

Lifter height - I installed LS7s which "reportedly" are .050" taller than the 2003 LQ9 lifters.

Given this info, and assuming the valve spring installed height is the same, lets do some math...

.070" preload with 7.380" PRs
change head gasket, preload goes to .081"
change lifters - Preload goes to .131"
Adjust PR length for .070 preload gives a .061" shorter PR.
7.380 minus .061" gets us to a 7.319" PR for .070" preload
7.325" PR gives us .076" preload
7.300" PR (whats installed now) produces .056" preload (on the loose side of acceptable range)
7.350" PR produces .096" preload - too much for my liking.

7.325" is the winner!!! (provided the spring installed height is the same as factory). That is the only variable.

Lesson learned - always get adjustable rocker arms.