Quick Q for PRC .675" spring guys & 20+psi....030" shim??
06-27-2013, 10:16 PM
#1
Quick Q for PRC .675" spring guys & 20+psi....030" shim?? Hey guys a buddy of mine and i are going to install a new set of springs in the next week or so and was wondering what shim you're using with stock valves and .675" PRC springs and 20+ psi to prevent valve float via adequate closed seat pressure. kind of an odd question, but i know plenty of you are running this spring so figured wth. btw i'll be using the titanium retainers and these are on 317 heads.
btw, had no signs of float at 11 psi on my .650" springs/steel retainers but by 14 psi it was starting to show up.
thanks!
btw, had no signs of float at 11 psi on my .650" springs/steel retainers but by 14 psi it was starting to show up.
thanks!
Last edited by PRAY HRD; 06-28-2013 at 11:47 AM.
06-28-2013, 07:27 PM
#2
I don't run those springs but I always shim my springs with in .050" of coil bind. There are way too many variables to give a blanket number on what shim to use; valve job depth, valve face wear, retainer wear, retainer angle, valve keeper groove, valve keepers and the lift of your cam. When you set everything up use a valve install height micrometer and you will be surprised at the difference you need in shims from one valve to the next.
06-29-2013, 02:36 AM
#4
No problem man, I will be a little more specific on setting up your springs with in .050" of coil bind. Here is the info I found on your springs
Specs:
Install Height: 1.810"
Closed Spring Pressure: 148lbs @ 1.810"
Open Spring Pressure: 450 lb. @ .600" lift
Open Spring Pressure: 490 lb. @ .675" lift
Maximum Spring Lift: .675"
Coil Bind 1.060"
Spring Rate: 483lbs/in
After looking at these specs I realize these are seriously stout springs, maybe too much for a hydraulic roller cam as you really don't want to run much more than 400lbs open pressure. Seat pressure could be shimmed up a little bit to be around 170-180 but that creates the problem of way too much open pressure. Valve float can occur on a turbo car from lack of seat pressure as the back pressure can blow your exhaust valves open. Keep in mind 400 + lbs of open pressure will be very hard on a hydraulic roller lifters and stock rockers if you run them.
Normally what I would do to shim within .050" of coil bind (this improves spring life and valve control) is take the coil bind number and add .050" to it. So take 1.06" + .050" = 1.11". Now add the lift of your cam, lets use .600" lift for example. 1.11 + .6 = 1.71" installed height. But I'd never do that with these springs. It's best to measure every spring on a spring height tester as they can vary quite a bit from manufacture spec to find the "true" height of which they coil bind at.
Honestly my best advice to you would be to sell these springs and contact Brian Tooley for a proper set of springs for your setup.
Btw here is the spring height micrometer I was talking about.
Specs:
Install Height: 1.810"
Closed Spring Pressure: 148lbs @ 1.810"
Open Spring Pressure: 450 lb. @ .600" lift
Open Spring Pressure: 490 lb. @ .675" lift
Maximum Spring Lift: .675"
Coil Bind 1.060"
Spring Rate: 483lbs/in
After looking at these specs I realize these are seriously stout springs, maybe too much for a hydraulic roller cam as you really don't want to run much more than 400lbs open pressure. Seat pressure could be shimmed up a little bit to be around 170-180 but that creates the problem of way too much open pressure. Valve float can occur on a turbo car from lack of seat pressure as the back pressure can blow your exhaust valves open. Keep in mind 400 + lbs of open pressure will be very hard on a hydraulic roller lifters and stock rockers if you run them.
Normally what I would do to shim within .050" of coil bind (this improves spring life and valve control) is take the coil bind number and add .050" to it. So take 1.06" + .050" = 1.11". Now add the lift of your cam, lets use .600" lift for example. 1.11 + .6 = 1.71" installed height. But I'd never do that with these springs. It's best to measure every spring on a spring height tester as they can vary quite a bit from manufacture spec to find the "true" height of which they coil bind at.
Honestly my best advice to you would be to sell these springs and contact Brian Tooley for a proper set of springs for your setup.
Btw here is the spring height micrometer I was talking about.
06-29-2013, 10:37 AM
#5
well i'm just picked up stock rockers with the trunion upgrade from brian tooley so i will be running those with this setup. and these are the springs speed inc suggested i get so i'll be running them. my buddy had the tools to do it, all but the spring pressure tester i think. but we're gonna track one down or purchase one before doing the swap. and yea, the cam is a 595/608 lift (brute speed blower cam). this is great info! 
06-29-2013, 04:40 PM
#6
If you were previously running roller rockers I bet you were seeing valve float. Stock rockers are about the lightest setup you can run, it's all about the weight over the tip of the valve. Look how heavy a roller rocker is with it's large roller over the tip of the valve vs. a stock rocker. The swap to stock rockers in itself should eliminate your valve float issues. Good luck and keep us updated!
06-29-2013, 07:06 PM
#7
i did actually and brian said the same thing was possible. i had the HS rockers and was the reason i swapped to stockers, with the better trunions of course. i've thought about taking it to the dyno to see if it eliminates it or not. hell i've even thought about keeping my springs and just adding a .015" shim and seeing how it does. hate to throw time & money at it and not stop the issue though.
