anyone ever shim comp 921's

Reply Subscribe

Thread Tools

Search this Thread

Apr 25, 2009 | 09:48 PM

52172

Thread Starter

TECH Junkie

iTrader: (2)

Joined: Jul 2003

Posts: 3,489

Likes: 1

From: Buellton Ca

anyone ever shim comp 921's

I have a slight valve float problem from my comp pro mag roller rockers, but after reading the Gm high tech article on valve guide wear with cams over .550 lift I would rather not throw my stock rockers back in there. I would rather shim my comp 921 so that the spring rate is higher to help with the valve float problem. I am running manley valves and a comp 222/224/.581/114 cam with the 1.75 rockers and have valve float over 5600 rpms, but I really don't mind it that much since my motor will last longer with shifting at 5800 rpms. I am already making the numbers in my sig. I would like to be able to pull a couple hundred rpms more. Has ANYONE shimmed 921's ? I know I could fit a .040 shim in there and not be near coil bind. Do you think it would help reduce valve float?

Apr 27, 2009 | 01:52 PM

52172

Thread Starter

TECH Junkie

iTrader: (2)

Joined: Jul 2003

Posts: 3,489

Likes: 1

From: Buellton Ca

mods please delete post above its spam...... and anyone else ever shim 921's??

Apr 27, 2009 | 03:44 PM

MIGHTYMOUSE

TECH Senior Member

iTrader: (59)

Joined: Nov 2001

Posts: 10,018

Likes: 51

From: Virginia

i shimmed mine once, didnt help anything, of course i didnt have valve float turns out.. and i dont think you do either... unless they arent at the correct suggested height all ready.

my cam is a decent bit larger and it can pull clean beyond 7000. maybe start by geting your install height checked and make sure the springs are good.

Apr 27, 2009 | 08:34 PM

52172

Thread Starter

TECH Junkie

iTrader: (2)

Joined: Jul 2003

Posts: 3,489

Likes: 1

From: Buellton Ca

I think the install height should be good since they were professionally intalled and havn't been touched since. They have only 20k miles on them not very hard either. MM could you please take a look at this power tv show of my car on the dyno and stop the video when they show my dyno and let me know what you think the power falling off up top is if you don't think it is valve float? It fall off pretty good around 5600- 5800? I will have the springs checked, but am pretty sure they are fine. The seat pressure on the 921's is only 135 pounds I think shimming them would help my topend? Here is the link to the TV show. http://www.powertvonline.com/video_detail.php?mId=2896

Apr 27, 2009 | 09:26 PM

MIGHTYMOUSE

TECH Senior Member

iTrader: (59)

Joined: Nov 2001

Posts: 10,018

Likes: 51

From: Virginia

20k miles is a lot on a set of springs...

Apr 27, 2009 | 10:33 PM

Jimmy P

TECH Fanatic

iTrader: (177)

Joined: Jan 2004

Posts: 1,933

Likes: 1

From: USA

Quote:

20k miles is a lot on a set of springs...

I would have to agree. I bet if you put them on a pressure tester there is a good chance they wouldn't have as much pressure as they did brand new. PRC has came out with a new valve spring kit for $350. Looks promising..

Apr 28, 2009 | 08:36 AM

52172

Thread Starter

TECH Junkie

iTrader: (2)

Joined: Jul 2003

Posts: 3,489

Likes: 1

From: Buellton Ca

Sounds like I might have to swap out the valve springs.. Which are better the new prc or patriot exteme's? I want them to fit in the stock spring pocket? I just looked and the new prc's won't fit in the stock spring pocket. What does everyone recommend for springs in the stock pockets? I have the 921 complete kit is there a better springs that works with my kit or do I need to purchase a whole nother spring kit? Thanks

Last edited by 52172; Apr 28, 2009 at 10:32 AM.