It is my understanding that the installed spring height for this kit is 1.800” in an ls3. I am getting around 1.750” with no shims at all. Cam is a btr stage 3 N/A.
.631” max lift. Anyone seen this before?

 

You might have to call BTR on this one but most LS motor seem to be OK in the valve spring height department. If needed they sell +.050 locks and or a titanium retainers are thinner. A photo of the valve in question would help as to see where the retainer is setting up here (ie like setting up to low).

 

I got around 1.750" installed height as well on my GMPP LS3 heads with BTR 660s and titanium retainers, no shims. Just shim to within 0.050"-0.060" of coil bind and call it good. The lower installed height will give you more seat pressure which will help more than it hurts

On the BTR 660s, bind is advertised at 1.070", so .050" worth of shims will put you right on the money (for your .631" cam) once you take rocker, cam & pushrod deflection into account. Since I am running a more aggressive cam with a much heavier pushrod, I felt more comfortable with a 500lbs , .750" lift Cam Motion spring setup. I wound up selling the BTRs and set the Cam Motion springs @0.050" to bind on both intake & exhaust and it has been flawless for 2000 miles and counting with the 6l80e shifting at 7400 rpm
and pulling smoothly all the way up (7500 rpm limiter). (The Cam Motion setup installed height was around 1.780"
if I remember correctly)

 

Why would I need shims if I am already shorter than advertised? If I am at 1.750 and I take into account the .050 safety margin, that is 1.700. Then take off the lift of the cam and I would be at 1.069. If I add shims wouldn't that bring me closer to coil bind? Let me know if im wrong on this and also if anyone can find the coil bind spec for the .650”. Thanks

 

If your installed height is 1.750" and we know that the BTR 660 spring coil binds is advertised at 1.070" that leaves us .680" left.

Subtracting the usual 0.050" coil bind clearance leaves .630" lift cam which is exactly what I am seeing the LS3 BTR Stage 3 intake lift is advertised at (.630")

So you were correct, I had made a mistake in my previous post 680 - .630 (your lift) = 0.050". You don't need any shims and you will have 0.050" + clearance to bind as is (taking into account the valvetrain flex)

Again, I was incorrect, I must have jumbled my numbers. You won't need ANY shims to have roughly .050" clearance to bind at .630 lift. (looking at my notes, I didn't need any shims and frankly had questionable clearance of .039" with my cam--it didn't matter as I didnt stay with the BTR 660s)

Looks like BTR Stage 3 (LS3) is .615" lift on exhaust so if you have the same 1.750" installed height on exhaust side you can pop a Comp 0.015" shim under the exhaust spring seat and be right on the money.

 

Do the .650” springs have a different coil bind because I cannot find it on btr’s website. I just dont wanna tear my car apart again because I messed up on this. I was gonna call them later today but just wondering.

 

Do you have BTR .660s or BTR .650s?

660s are a 400 lbs spring with a 1.070 coil bind

650s are a 392 lbs spring with a 1.020 coil bind
BTR .650 Spring Specs:

Installed Height: 1.800"
-Closed Spring Pressure: 160lbs @ 1.800"
-Open Spring Pressure: 425lbs @ 1.125"
-Maximum Spring Lift: .650"
-Coil Bind 1.020"
-Spring Rate: 392lbs/in

If you have a 650 spring with the 1.020 coil bind, you would ADD a 0.050" shim to get exactly 0.050" coil bind clearance.

BTR .660 spring specs:•155 lbs @ 1.780"

•380 lbs @ 1.180"

•400 lbs @ 1.130

•Coil bind @ 1.070"

 

See, that is my problem, I have the .650 springs but my installed height is 1.750. So If I shim it .050” I will be .050 away from coil bind but my installed height will go down to 1.700”. Not 1.800”

 

I understand. I did the math for you! I fully get your installed height is 1.750". Coil bind on the 650 is 1.020".

1.750 - 1.020 = .730"

Your cam has .630" intake lift

.730" - .630" = .100"

.100 - 0.050" (shims) = 0.050" coil bind clearance

REMEMBER, I was doing the old math off of the BTR 660
which binds at 1.070". the BTR 650 (which you have) binds at 1.020" (0.050" MORE clearance than the 1.070" of the BTR 660) so to get to the preferred 0.050" coil bind at full lift on your cam, you will need a 0.050" shim under the spring seat.

Pay no attention to what the installed height is "supposed" to be. We are doing the math off of your ACTUAL installed height and ACTUAL spring coil bind. Those are the numbers that matter.

Now, if you set up your intake side with NO extra shims, you will have .100" coil bind clearance, which isn't "bad" but it lets the spring oscillate and move around at high rpm. The whole point of the 0.050" clearance to coil bind is that the coils touch one another and damp the whole assembly. Whenever I am setting up a valvetrain, I shoot for 0.050"
to bind. Any more and you lower the rpm limit of the valvetrain.

0.050" clearance is not "between" the coils, it is the ACTUAL point where the spring locks up. If you want to get SUPER accurate you can check bind yourself by squeezing the spring in a vice until it cannot be compressed any further, then measuring its height.

 

Okay, I just wasn’t sure if the smaller installed height would have too much spring pressure when it is closed. But thank you for the help. I should be able to finish the heads tonight with the help.

 

that's is a 392 lb rate spring. It is easy to figure out how much more open pressure you will get from the extra 0.050" and it isn't excessive. Adding the extra 0.050" shim to give you 0.050" coil bind clearance will increase the open rate by 19.6 lbs (compared to the 0.100" clearance to bind of no added shims)

 

Okay thanks. Can I ask where you found all the specs?

 

I am not so sure the specs before were accurate, they don't match this below

This is from Speed inc:

Racing BTR .650" Max Pressure Dual Spring w/Titanium Retainer Kits

BTR .650" Lift Dual Spring Kit for LS engines using roller rocker arms, or track only applications using stock rockers. Includes springs, matching titanium retainers, your choice of locators for stock or bronze guides, locks and seals. Spring specs are 150 lbs @ 1.800", 420 lbs @ 1.200" 450 lbs @ 1.150" coil bind @ 1.100" This is a drop in spring kit for the following engines: LS1 LS2 LS3 LS4 LS6 L76 L92 L99 LQ4 LQ9 L33 LSA. This kit will not fit LS9 engines.

According to this and other distributors, coil bind is 1.100" for the 650 springs. I apologize for the misinformation.

I would call BTR directly and ask just to get it from the source. It is mind blowing they don't have the 650 data on their own site.

 

So I emailed btr’s customer service and they told me the .650” kit had a coil bind of 1.000”.
Now I really don’t know what to do. And I already put them in the heads.

 

I have part #sk-703 not sk-002. Btr’s customer service said coil bind is 1.000”