Asmodeus

I would have thought putting shims in the valve seat would just compress the spring farther, and allow for less lift. How does a spring need to be shimmed for a .650 spring to run a .640 lobe with .050 left to coil bind? I just can't wrap my mind around how you can make a spring "taller" with shims. Do you need longer valve stemmed valves? I'm sure the shop I have do my H/C combo will know what to do, but I'd like to understand it.

white2001s10

iTrader: (4)

You can either use longer valves, offset retainers, cut the spring pockets deeper, or in mild cases remove the spring seats and replace with thinner steel shims.

In either case you are increasing the install height of the spring. This allows more travel before bind, but lowers your seat pressure.

Asmodeus

but they said for the cam with .640 lift lsk lobes, to "shim the springs to within .050 of coil bind." They never said anything about touching the heads, and recommended the comp 921's

JL ws-6

iTrader: (50)

By shimming the spring you are increasing the seat pressure that the valve and valvetrain sees, what you are doing is preloading the spring so that it will take more initial force to get the spring to open, and will put the entire range of motion that the valve sees at a higher load point in the springs total movement. It is a way to make a spring behave as if it was stiffer then it actually is.

Hope this helps.....

Asmodeus

so what do they mean when they say "shim the 921's to within .050 of coil bind", when the cam I bought would put that spring within .011 of coil bind? and the PRC duals within .021? Is that too close? Acceptable?

Also, Isn't that lobe going to beat the crap out of that spring? I was told that with shimming they would last as long as if they were on an X-ER lobe. Before I buy the springs for this cam, I just want to be sure.

JL ws-6

iTrader: (50)

Sounds like you may not have enough spring if that's the case... not sure what other spring is a viable option.

Asmodeus

These lobes are already in LS1's/LS6's. Comp 921's are recommended. I was told, also by someone on this board running one of these cams, to use the 921's and shim them to .050 of coil bind. Same as a vendor. I just want to know how it's possible. The numbers don't add up.

Patrick G

iTrader: (14)

The .650 max lift of Comp 921s is a rough guideline. With LSK lobes running .650" lift, there has been room to still shim them and have .050" of coil bind clearance. Haven't tried on the PRC/PP/Manley duals, but it may be similar.

ThirdGenLS1

iTrader: (11)

You want to shoot for .040 to .060 of coil bind to do this you need to find out what coil bind is for your spring. Usualy you can find out off of comp's website but measing it your self is your best bet cause they do vary.

Just stick the spring in a vise and compress it till the coil binds and then take a measurment. For instance my comps were all right around 1.035 give or take a few tenths , now take that number add .050(for the coil bind) to it so now you have 1.085 add your lift of your cam to that which in my case was .644(intake) so now you have 1.729, this is your desired install height.

Now you need to find your install height of the spring with no shims, you need a valve spring mic for this and stick it in place of your spirng on the head and find its install height which for me was right around 1.78.

Now subtract the total height to your desired spring height and you get how much you need to shim it. 1.78 - 1.729 = .051, so you want to shim your spring .051 to get you right around .050 coil bind and in my case my shim kit came with .015 and .030 shims so i used one of both to get me a .045 shim which will get me with in my .06-.04 coil bind i was looking for.

So for a recap the equation is

Coil Bind + .050 + lift = Desiered install height

Install height - Desiered install height = your shim

Hope that isn't to comfusing but thats the best i could explain it.

Justin

JZ'sTA

iTrader: (23)

acturally that was a very good example, and easy to understand.

Asmodeus

yes, you and patrick definately explained a lot about it to me.