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Who’s got experience measuring installed spring height? New btr stage 2 boost cam purchased for my turbo. Running stock 243 heads.
Ordered the BTR platinum spring kit with titanium retainers and .660” lift. Also purchased their spring micrometer to measure install height. They want 1.78” install height and here are my measurements for each head and valve.
I’m pretty much within .020” from my smallest and largest measurement. Should I shim my exhaust valves or leave them be?
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Also had someone tell me I should measure each spring too, I think that’s overkill
The exhausts are already closer than the intakes. If you shim them up their installed height will decrease further. Probably not a good idea to do that.
What is the cam's peak lift? How much shim is in them now to get to where they are?
The exhausts are already closer than the intakes. If you shim them up their installed height will decrease further. Probably not a good idea to do that.
What is the cam's peak lift? How much shim is in them now to get to where they are?
The exhausts are already closer than the intakes. If you shim them up their installed height will decrease further. Probably not a good idea to do that.
What is the cam's peak lift? How much shim is in them now to get to where they are?
I thought if the number is lower you shim it to bring the value up. Maybe I have it backwards. I read somewhere for boost it doesn’t hurt to have extra spring pressure too
Yup. You do. There's some fixed distance between the top of the spring seat and the bottom of the retainer. The more of it you take up with shim, the less is left for the spring.
Yes for boost (or any aggressive usage for that matter) having a bit more than the minimum "spec" spring pressure is usually better. However, the more you shim a spring, the greater the stress in it, and therefore, the shorter its life is likely to be. This is in addition to the dynamic effects of resonances and whatnot; go beat on a spring with a hammer and see what it does, and realize that that's EXACTLY what's going on in your engine. If the coils are too close together, they'll touch when the spring goes "boioioiiinnnggg" at each operation; this can be used to good effect to control those resonances, butt also tends to decrease spring life, by generating extra heat. It's a tradeoff. So in short, shimming them up to lower installed height than their "spec", is likely to lead to shorter life, even if it possibly improves control of the valve.
If anything, you could shim the intakes up to drop their installed height to closer to the exhausts. There's probably not much payoff in it butt since the exhausts are already that close, that's gonna be what your spring lifetime is controlled by, so it wouldn't make it any worse; the spring rate isn't linear, butt if you take the pressure difference from 0 lift to .600", it's about .375 lb per .001", so if you tighten up the intakes by .020" you'd pick up about 7½ lbs of seat pressure on them. Again, not sure how much benefit there would be in that; you'd essentially also be lowering the "max lift" that the springs can tolerate from .660" to .640", which with a cam that's .618" nominal, not sure that's a good idea. It's a tradeoff of those 2 properties as well.
Yup. You do. There's some fixed distance between the top of the spring seat and the bottom of the retainer. The more of it you take up with shim, the less is left for the spring.
Yes for boost (or any aggressive usage for that matter) having a bit more than the minimum "spec" spring pressure is usually better. However, the more you shim a spring, the greater the stress in it, and therefore, the shorter its life is likely to be. This is in addition to the dynamic effects of resonances and whatnot; go beat on a spring with a hammer and see what it does, and realize that that's EXACTLY what's going on in your engine. If the coils are too close together, they'll touch when the spring goes "boioioiiinnnggg" at each operation; this can be used to good effect to control those resonances, butt also tends to decrease spring life, by generating extra heat. It's a tradeoff. So in short, shimming them up to lower installed height than their "spec", is likely to lead to shorter life, even if it possibly improves control of the valve.
If anything, you could shim the intakes up to drop their installed height to closer to the exhausts. There's probably not much payoff in it butt since the exhausts are already that close, that's gonna be what your spring lifetime is controlled by, so it wouldn't make it any worse; the spring rate isn't linear, butt if you take the pressure difference from 0 lift to .600", it's about .375 lb per .001", so if you tighten up the intakes by .020" you'd pick up about 7½ lbs of seat pressure on them. Again, not sure how much benefit there would be in that; you'd essentially also be lowering the "max lift" that the springs can tolerate from .660" to .640", which with a cam that's .618" nominal, not sure that's a good idea. It's a tradeoff of those 2 properties as well.
thanks for all your input man! This is my first engine build so still learning. I know enough to be dangerous but stuck on the spring stuff. I should have mentioned this is a forged 6.0, with 85/96 turbo and running a BTR stage 2 boost cam. power goal is 950-1000. Maybe 18-20 psi. Just a street car. As I mentioned the stage 2 cam Intake and exhaust is both .618”. Got the dual BTR platinum dual springs kit .660” springs with titanium retainers.
So you recommend I shim the intakes maybe .200 each? Or machine the seats of the exhausts to bring the value up.
I am slightly concerned about valve clearance though, but my new forged pistons do have valve reliefs pretty deep.
i did measure with a BTR micrometer with the seats installed. They are a two piece where the seat and seal are separated. I just installed seat, mic, hat and retainers and took measurements.
I wouldn't shim the intakes .200". Maybe .020" at the most. Shim kits usually have .015" .030" and .060" so I'd just add .015"s to the intakes if I was going to do anything at all to it.
.005" is about the thickness of 2 sheets of copy paper. A very tiny increment. Too fine of a detail to make any significant difference.
I wouldn't shim the intakes .200". Maybe .020" at the most. Shim kits usually have .015" .030" and .060" so I'd just add .015"s to the intakes if I was going to do anything at all to it.
.005" is about the thickness of 2 sheets of copy paper. A very tiny increment. Too fine of a detail to make any significant difference.
yeah sorry not sure why I typed .200 I meant .020. Bringing the intakes to 1.765. Thanks for the help!
Hydraulic or solid roller lifters? If solid, you can subtract the cam's cold clearance from total lift. If hydraulic, the plunger might eat a couple thousandths before it locks up. Hopefully your pushrods won't flex and eat up some lift. I'd call BTR and ask them what they think is a healthy minimum distance to bind. They do a lot of Spintron testing so they are likely to really understand their product. 20 PSI of boost against a large valve will try to keep that valve open and the spring is all you have to overcome that. I wouldn't shim any more than 0.015" but would defer to what BTR says.
Hydraulic or solid roller lifters? If solid, you can subtract the cam's cold clearance from total lift. If hydraulic, the plunger might eat a couple thousandths before it locks up. Hopefully your pushrods won't flex and eat up some lift. I'd call BTR and ask them what they think is a healthy minimum distance to bind. They do a lot of Spintron testing so they are likely to really understand their product. 20 PSI of boost against a large valve will try to keep that valve open and the spring is all you have to overcome that. I wouldn't shim any more than 0.015" but would defer to what BTR says.
yeah I talked with BTR they recommended .015” shims on intake valves! And really if my math is correct….
If my install height is minimum 1.760, my cam lift is .618” that should compress spring to 1.142” and then adding another .060” for safety that brings the value to 1.082”. And coil bind starts on these springs at 1.070”. So I have like another .012” of clearance
I would leave the intakes where they are at the 1.78". If you really want, you could add 0.020" to the intakes to get to ~1.76" to match the exhaust side. No need to go tighter than 1.760"
I would leave the intakes where they are at the 1.78". If you really want, you could add 0.020" to the intakes to get to ~1.76" to match the exhaust side. No need to go tighter than 1.760"
im gonna be adding .015” shim to each intake. My smallest value at .015” shim would be 1.760
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Setting spring height 
