Thank you.

 

Hey anytime.

If you want, I can direct you to the exclusive LS1 MFG's of shims as well.

I think there's only 11,799 links for special LS1 shims however.

You may have to call a metal shop to cut some extras for your app.

 

I think I'm ok... but you proven my point.

 

in this scenario, you are talking about two different springs. the same spring will not be 125 lbs at 1.800 and 1.770 height. so yes the harmonics will be different between the two. just like was said. you do not shnge the spring rate by adding shims. the spring rate is determined by the design of the spring itself. thickness of coils, how many per inch, etc...

there are a few reasons that comes to mind as to why you would need to shim a couple of springs to meet the same pressure. installed height not correct for that valve due to variances in the spring pocket on the head being the main reason. valve stem length different. valve seat cut deeper than the others.

unless there is something seriously wrong with the spring, installing shims to get proper seat pressure is fine. of course so long as you do your math in making sure coil bind doesn't happen. but .030 is nothing wrong.

 

ACtually, I'm referring to the same spring set. One of them, or a few are
out of spec. The spring(s) which needs 0.030" to achieve the same seat
pressure will have different properties.

Agree.

 

as was told earlier. the spring rate does not change no matter how many shims you put under them. if the spring has 350 in/lbs rate, that will remain 350 in/lbs no matter what. that is determined by the spring diameter and how many coils per inch. the only thing you are changing is the installed height and seat pressure. the open pressure doesn't change.

what do you do if the spring pocket was cut, say .015" deeper than the rest of them on the head? throw the head out? cut the rest to the same depth? or just put the .015" shim under it to make it the same as the other seven spring pockets to achieve the same installed height?

now, if the machine shop had to cut the valve seat .015" deeper than the rest, then i'd look at that as needing replacement if it made the valve seat too thin/wide and set the valve too deep in the pocket there. don't want to suck a valve into the pocket.

everything isa case by case basis. but, just to say .030" is too much and you have to find a different spring is just like you said. just your opinion. nothing wrong with that. but on the same token, nothing wrong with using a .030" shim get achieve what you need isn't wrong either. i also agree that if you can find a spring that'll meet your requirements without shimming, i'm all for it as well. on my last set of dart heads i had, it took about 3 hours of looking through all those books of springs, offset locks, offset retainers, etc... to find one close enough to seat pressure, spring rate, and open pressure to get one close enough. still, i had to use a .015" shim to get what i needed. and every part was new. head, valves, springs, everything.

 

Agree...but that's not what I'm talking about.

If a spring is spec'd to be 125# @ 1.8" install height, we expect the entire
set to be within tolerance. If one of the springs in that set need 0.030"
to achieve 125# on the seat, the spring is out of spec. It will therefore have
a different "spring rate" and the harmonics, etc. will not be the same throughout.

I would use a 0.015" shim. Again, if you read back, my comments regarding
large shims are not against setting install height.

That's more along the lines I'm promoting. Here's an example that might
show what I'm trying to get across (keep in mind, this is my opinion):

Peak Shift RPM: ~6200 RPM
Rocker Ratio: 1.7 (stock valve weight)
Valve lift: 0.620"/0.620"
Hyrdaulic lifter Pre-load: 0.050"

Stock spring height is 1.8" on a stock head (*head is true, and clearanced)

Using Crane's 832 (Part#: 144832)

Install height: 1.8"
Seat Pressure: 112 lbs. @ 1.800"
Open Pressure: 352 lbs. @ 1.150"
Coil Bind: 1.045"
Spring Rate: 352 lbs./in.

Technician A wants to use a 0.030" shim to get ~ 125# on the seat.

With a recommended 0.060" clearance before coil bind, using the above
cam specs and lifter pre-load, what problem might occur?

 

Nothing wil occur. If .080 preload is too much, get a shorter pushrod

 

well in using the math, i take the coil bind(1.045) and add in the amount of total valve lift(.620). then add the .030 shim. that gives me a minimum height of 1.695" that leaves a .105" clearance using the 1.800" installed height. plenty of room. did i miss something there? you wanted .060" clearance. you got .105". leaves .045".

or doing it the other way. 1.800" - .030" shim = 1.770" 1.045" + .620" + .060" = 1.725" still leaves .045" no matter how you look at it.

that means there is something wrong with the spring in that case. so yes, the spring needs to be replaced.

 

lifter preload is determined by pushrod length in non-adjustable valvetrains. in adjustable valvetrains, you can change lifter preload to fit your needs so long as the geometry doesn't get messed up.

preload has nothing to do with installed height of the springs and the clearance between coil bind and total valve lift.

 

What about valve float, and lifter pump up (0.050 pre-load)?

Just thinking, once you begin cutting into the clearance window, it`s a thin
edge.

If that spring was used to the max. recommended valve lift of 0.650, the
shims would be even more of an issue.

As the springs get weak, and/or RPM increases that clearnace window
is more and more your friend.

That`s why I choose to shim for spring height, and not for pressure.

 

what about it? that's where the .060" additional clearance comes into mind. minimum required is .060". in the scenario you just put up, there is .105" clearance. .045" more than asked for.

even at the 1.770" using a .030" shim, you still have plenty of room. 1.770" - .620" - .060" = 1.090" - 1.045"(coil bind) = .045"

 

Don't forget though, that 0.060" clearance is also accounting for coil deflection and
harmonics.

Once the lifter goes over the nose of the cam lobe, the valve, rod, rocker,
spring all have momentum. They all want to continue opening.

Even the spring coils continue moving in the 'open' direction for a period of
time before the coil energy can return the opposing force.

This is more apparent at higher RPM when the effective mass of the components
becomes higher due to the velocity of the reciprotating parts.

 

in using you scenario you put up. we still have a total of .105" clearance for any and all things to happen at the 1.800" installed height. and at the 1.770" installed height, you have .060" clearance. it's covered. and the .060" is a padded number anyway.

 

I'm sure it's a padded number as well. The spring MFG's wouldn't advertise
clearance values on the edge.

Even if that clearance value is doubled, think about running the spring coils
to within half a spark plug gap.

That's pretty brave. In any case, thanks for the level headed tech talk.

 

hey, i do that sometimes.

 

I like to run springs on the safe limit of coil bind, that sounds exactly how Id set them up

 

Interesting discussion.

Let me interject one thing regarding harmonics and valve float. Now this isn't theory, but the actual experience I had. As some of you already know, I started out with a set of SLP 1.85 rockers on my car. The SLPs are made by the manufacturer of the OEM rockers and are identical to them except for their ratio. I decided to test a set of the Crane 1.80 Quick-Lift roller rockers and so swapped a set in. At this time, I was also running a new set of PRC dual valve springs with titanium retainers and seats.

When we dynoed the car, the motor nearly equalled the power I was making with the SLP 1.85s (389 rwhp vs. 392 rwhp) even though I lost ~.010" of valve lift due to the lower ratio. I also reached peak power sooner by ~200 rpm. That was the good news. The bad news was that the motor had a wicked power dip at ~6000 rpm that it recovered from, but not fully. The dip was very pronounced on the graph looking almost like a capital U. In speaking to Crane, it was determined that this power dip was being created by valve spring harmonics and they suggested I replace the PRC duals with a set of Crane dual valve springs shimmed .060". I got a Crane dual valve spring set which included their own titanium retainers and seats. I also bought a Comp hardened shim set (which I mentioned in a previous post) and used the .060" shims from it.
After installing the new springs, retainers, etc, we redynoed the car. Results were that the power dip was completely eliminated and I picked up 10 rwhp and 8 rwtq over the SLP 1.85s and 12 rwhp over the run with the power dip going from 389 rwhp to 402 rwhp.

I admittedly don't know enough about valve spring science to say whether the shims affected the harmonics of the Crane dual valve springs or not, but the evidence is that, if they did, it was in a positive and not a negative way.
This power increase has since been confirmed at the drag strip as I'm running my best times ever and am now "oh so close" to breaking into the 11s (see sig).

 

Interesting story, and good trouble-shooting.

I'd say there were too many variables changed to pin-point the harmonic correction
to just the shim (springs, retainers, locks, etc.).

I'd say the spring swap was the primary reason for the power curve
improvement (better suited pressures across the entire valve motion profile).

Good luck hitting 11's!

 

I totally agree with your assessment. I too believe the real difference was the spring swap. I just wanted to point out that the shimming didn't hurt me.

Thanks! If the weather cooperates I'm going to try again Friday night. It should be a little cooler so if I can get a good launch I should be there.