I need a little help guys and I hope some one can point me in the right direction. I have a set of NIB Absolute Speed stage2.5 5.3l heads Milled: ~.025 Springs: Comp 977 with Ti retainers Valves: 2.04 and 1.575 (REV stainless steel intake and exhaust valves). My engine build has change alot in the last 2 months and I want to get a bigger cam to go with the 383 stroker but I want to use the heads I have because the flow #s rock. The cams I keep getting informed to run are over the .600 the springs are rated for and I need to know if they will be ok to run or not. I have looked at a few cams like the T-rex and a custom one I came acrossed but the lift range is .608/.612 and the custom one is .617/.634

I have Comp R lifters and Jesel adj. shaft mounted rockers.

I am about to just order a MS3 and call it a day! Oh for those that will recommend a custom cam...I called a "good" shop and have waited and waited for a call back but I have not heard anything yet.

 

Looks like about .655..... Although, I'm pretty sure that those valves are .050 or .100 longer than stock, not sure if that affects things and if so how much.

Here are some specs from Comps website:

Seat load: 155@1.850
Open load: 419@1.250
Coil bind: 1.195
Rate (lbs/in): 441

Shawn

 

I was at Comps site a day or two ago. Maybe I just read the specs wrong. Thanks for the help.

 

Go
here
and scroll down to page 338...

 

BTW, those heads will ROCK with a bigger cam, they were ported with a G5X3/4 in mind, you might wanna try a G5X3 or G5X4....

 

I'm now running Comp 977's + Comp R 850's + .598/632 lift cam. Car pulls clean to 7100 rpms.

 

A stock length valve yeilds an installed height of around 1.800, so with .050" clearance from peak lift to coil bind that puts you at .550" lift. I never have understood how AS got that spring to work, unless its a spring "similar" to the 977, kinda like when PP was using the Comp 977's, but they were not buying them from Comp.

 

I am running a .100 longer than stock set of Manley valves.

 

Are your springs shimmed???

 

Comp has a 921 that is made for the ls1. It has a higher rate and more pressure on and off the seat than the 918. It will also go to somewhere around .650 lift.
Check ther master catalog or call them. The have what you need.

 

What lifter do you have to use with it? Also can I just remove my Comp 978 and install these or do I need to have the heads machined?

 

Are the 921's the same outlet diameter as the 977's?

We shim the springs to get the right installed heighth, that is normal.

 

The 921's have a 1.300" diameter and will fit into your stock spring pockets. Comp also makes a kit that comes with springs, spring seats, ti retainers and viton pc seals....everything you need to upgrade. My catalog is at home but I think that they have a spring rate of 400...

Comps toll free is 1-800-999-0853

Hope this helps