Double check me please. - North East F-Body Association

Triaxle · #1 07-12-2011, 09:22 PM

Today I measured the install heights for my springs(918s). They all came out between 1.8 and 1.785. So with those numbers I'm thinking a .060 shim would be good for my cam (.561/.564). That works out like this:

1.785 - .564 = 1.221. Then -.060 shim = 1.161. With 1.100 coil bind = .61 from coil bind

I've never installed springs before, so let me know if this is the right way to go. Thanks

ILuvPizzaTimes10 · #2 07-12-2011, 09:32 PM

I'm hoping these are the new versions? If not do not. Install them a lot of guys have broken them(old version). Installed height is all about spring pressure and vale train geometry. Just picking a number doesn't work. Are they used or new? If used have them checked at your installed height. To make sure they are still at the right pressures. Now if your at 1.8-1.785 for heights and you shim them down further your spring pressure will be very high on seat. And its a lot harsher on the lifter and rockers to push the valve open. Id say stick with there advised height unless you have all the tools to make sure your not shooting way past 130# of seat pressure. If you do the open pressure will be past 500 if I m reading the chart right for these springs.

Triaxle · #3 07-12-2011, 09:49 PM

Quote:

Originally Posted by ILuvPizzaTimes10

I'm hoping these are the new versions? If not do not. Install them a lot of guys have broken them(old version). Installed height is all about spring pressure and vale train geometry. Just picking a number doesn't work. Are they used or new? If used have them checked at your installed height. To make sure they are still at the right pressures. Now if your at 1.8-1.785 for heights and you shim them down further your spring pressure will be very high on seat. And its a lot harsher on the lifter and rockers to push the valve open. Id say stick with there advised height unless you have all the tools to make sure your not shooting way past 130# of seat pressure. If you do the open pressure will be past 500 if I m reading the chart right for these springs.

Yes these are the new version, unused. What I'm coming up with is 153 on the seat, opposed to 125 at 1.800. And 362 open pressure. But I'm working on the assumption that I would rather have more spring pressure than not enough. I should prolly give Comp a call and see what they recommend for these lobes.

ILuvPizzaTimes10 · #4 07-12-2011, 10:14 PM

125# is not too bad for seat pressure unless your running big boost. The 325 open is low and you don't want valve float. Calling comp might be your best idea to make sure your right on. I've had heads come back and blow up from all the little shit not being 100% right.

84ta406 · #5 07-12-2011, 10:16 PM

Take the height from the spring seat to the bottom side of the retainer with a mic, then take the installed height of the spring, subtract and you'll get your shim sizes. Like pizza said, too much shim is VERY HARSH on the valvetrain.

Mine were like 130 at the seat and 343 open at a 1.8 install

Triaxle · #6 07-12-2011, 10:18 PM

Quote:

Originally Posted by ILuvPizzaTimes10

125# is not too bad for seat pressure unless your running big boost. The 325 open is low and you don't want valve float. Calling comp might be your best idea to make sure your right on. I've had heads come back and blow up from all the little shit not being 100% right.

No I won't be running any boost. And also the cam is supposed to peak close to 6k rpm so I won't be revving it too high. But yea thanks for the replies I'll prolly call Comp tomorrow.

ILuvPizzaTimes10 · #7 07-12-2011, 10:27 PM

Summitracing has tech support till I think 7pm. Give em a try there pretty good over there.

Triaxle · #8 07-12-2011, 10:32 PM

I plugged in the wrong spring rates. I was looking at the 915 spring rate so I would be looking at this instead:

153 seat and 362 open. And thats just by going off of the numbers comp gives, not physically measuring the springs. I don't have the tool for that

ILuvPizzaTimes10 · #9 07-12-2011, 10:35 PM

Measure the spring I have never seen a spring to be right on the spec. Mine were 15pounds off. So they got a little more shim than we thought we needed. As I sed have em checked. At the height you want em installed. A machine shop will do this for free or verrryy cheap.

Triaxle · #10 07-12-2011, 10:39 PM

Hmm yea thats an easy enough thing to do. I've heard that a new spring will loosen up a little bit after its been heat cycled and run a little bit. Any truth to that you know of?