Pushrod length?
Thread Starter
Safety Car
Joined: Sep 2003
Posts: 3,558
Likes: 2
From: Cape Coral FL
Pushrod length?
After browsing some of the supporting tuners and vendors sites I thought 7.4" was stock length. After all that is what they are advertised as. Then I looked up the part number for a stock LS1 pushrod and found the stock length. It was 7.318". I know there is great variance in pushrod length depending on endcap size, style, and manufacturer measurement standards. It caused my eybrows to shoot up, because I just replaced my stock pushrods with TR 7.4's. I have had them in the car for about 1000 miles now and have been to the track a few times and nailed it a few more. Zero problems, and valvetrain is quiet as stock. When I installed them I didn't check for lash, because I thought they were 'stock' length. Are my lifters making all that length up? After the install I read a post that someone had measured the TR pushrods and found them to be 7.424, I think. I thought I understood this stuff, but the more I learn, the less I know.
Team Owner
Joined: Sep 2001
Posts: 23,283
Likes: 906
From: Lake Elsinore, CA
Nominal stock pushrod length is 7.400" but manufacturing tolerances have to be factored in. Without a machine drawing, you'll never know the manufacturing tolerance for sure.
My heads were milled .030" so I went with 7.350" pr's since they generally come in .050" increments. They rest is made up by the travel in the hydraulic lifters. Some tuners use shims under the rocker bolts to make up some of the preload.
Check out one of CompCam's tech pages on pushrods:
http://www.compcams.com/Technical/Products/Pushrods/
My heads were milled .030" so I went with 7.350" pr's since they generally come in .050" increments. They rest is made up by the travel in the hydraulic lifters. Some tuners use shims under the rocker bolts to make up some of the preload.
Check out one of CompCam's tech pages on pushrods:
http://www.compcams.com/Technical/Products/Pushrods/
Advanced
Joined: Mar 2004
Posts: 65
Likes: 0
From: Howell MI
Originally Posted by ArKay99
After browsing some of the supporting tuners and vendors sites I thought 7.4" was stock length. After all that is what they are advertised as. Then I looked up the part number for a stock LS1 pushrod and found the stock length. It was 7.318". I know there is great variance in pushrod length depending on endcap size, style, and manufacturer measurement standards. It caused my eybrows to shoot up, because I just replaced my stock pushrods with TR 7.4's. I have had them in the car for about 1000 miles now and have been to the track a few times and nailed it a few more. Zero problems, and valvetrain is quiet as stock. When I installed them I didn't check for lash, because I thought they were 'stock' length. Are my lifters making all that length up? After the install I read a post that someone had measured the TR pushrods and found them to be 7.424, I think. I thought I understood this stuff, but the more I learn, the less I know.
Good Luck
Tony
Drifting
Joined: Apr 2002
Posts: 1,614
Likes: 1
From: DFW TX
The latest info from ls1tech indicates the stock length is 7.380, so 7.4's can be accomodated by the stock hydrualic lifter (.020 difference). If a cam change is done at the same time, many aftermarket cams have a base circle .030 smaller in radius, so the net change is .020(extra pushrod length) -.030(smaller base circle)= -.010(pushrod shorter than nominal), once again, within the range the lifter will tolerate. If the heads are milled, then within .010-.020 milling, you are still in a good range fom the calculations above.
Hope that helps
Hope that helps
