Originally Posted by DanZ28

TR recomends an install height of 1.770" which would be a .030" shim on the older Crane springs. I understand the newer spring with the blue stripe and a yellow stripe needs up to a .090" shim. Crane says you can shim them .060" and still run .640" lift safely...

Dan

Originally Posted by Mark Campbell from Crane

Sorry for the delayed response, but I was out of the state for a couple of days. There has been a good deal of misinformation about what shimming will and will not do. Shimming should not have a significant affect on valve spring life. It also doe not affect the harmonics of the spring but can affect the harmonic stimulation of the pushrod. It is necessary to provide adequate seat pressure to keep the valves from bouncing as they return to the seat. Fortunately, the LS1 valve train is relatively light and the large stock rocker ratio (1.7) multipies the seat pressure to help prevent bouncing of the lifter on the lobe. Our spring sets up at 112# at 1.800" installed height. We have purposely designed the spring with this seat pressure to allow shimming to the needs of the cam profile. We have kept the valve spring rate on the moderate side to keep the valve spring open loads from causing too much pushrod deflection at max lift. Too much open pressure will cause the pushrod to bend like a pole vaulters pole and cause an undesired "throwing of the valve" which means you have lost control of the valve train. Too much pressure and too high of a spring rate can cause just as many if not more problems than too light of a rate! (There are harmonic issues which are quite complex that relate to spring rate, lift rate of the lobe and rocker arm ratio that would take a text book to explain). If the seat pressure and spring rate are too high to start with, it's impossible to remove pressure!!. We also like the harmonics of this spring design over a wide range of applications. We feel our harmonics provide the best operation over the widest operating range of any spring on the market, and we have tested them all. I would recommend 120-125# of seat pressure for your application. A .030" shim should be the proper shim to place under the spring to achieve this seat pressure. This equates to a 1.765-1.770" installed height. With that seat pressure you should have no problems with valve train separation throughout your entire operating range (i.e. you will run into valve float problems from the inherent design characteristics of the lobe before you reach a critical harmonic in the spring!). Indiscriminately throwing valve spring shims under a spring is a sure way to disaster. We recommend measuring the istalled height of each valve spring and shimming as necessary to achieve the desired seat pressure. The seat pressure is the most important issue here and we have tried todesign a spring that provides maximum flexibility for maximum performance. We think we have succeeded. If you have any othe questions or issues, please feel free to contact me.

Originally Posted by Jason99T/A

The 1.770" install height was for use with the TReX's .608"/.612" of valve lift. The T1 cam can be shimmed quite a bit more if you feel comfortable with that. You want to run the spring around .050" from coil bind.

Jason

Originally Posted by DanZ28

I thought you would shim according to desired spring height and seat pressure for our particular application.