Math behind Valve Spring Selection?
Math behind Valve Spring Selection? 402 ci motor
LS3 intake/nw 92mm throttle body
823 heads, LS3 rockers, CHE trunnions, 11/32 .080 hardened pushrods, powder metal valve guides, Johnson 2116LSR lifters
GM Hollow Stem Intake Valves 2.165 - 12569427
GM Inconel exhaust valve upgrade 1.59 - #12612427
Spring specs are 155 lbs @ 1.780", 380 lbs @ 1.180", 400 lbs @ 1.130", Coil Bind 1.070"
FIS T6 V2 88/102 1.32 AR
I'm planning on running around 20-25lbs of boost, shift at 7300 RPM
Looking at 2 possible hydraulic cams on this new combo:
226/243 |.618"/.618" | 115 LSA +5
235/243 | .635”/.613” | LSA116.5 +6
So with rocker ratio of 1.7....
Cam #1 Intake max lift @ valve is 1.051, Exhaust max lift @ valve is 1.051 ?
Cam #2 Intake max lift @ valve is 1.080, Exhaust max lift @ valve 1.042 ?
Where I need more schooling is the how to determine if you have enough spring seat pressure. 2.165 intake valve
1.59 exhaust valve
11/32 stem area = 0.093 sq in
area of circle = pi * r^2.
intake valve size
2.165 = 3.6794 - .093 = 3.586 sq in
For 10 psi boost : 2.165" diameter intake valves, the seat pressure reduced 35.86 lbs, and @ 25 psi seat pressure is reduced to 89.65 lbs
The valve spring specs that will come with the heads are the BTR .660 SK001: 155 lbs @ 1.780", 380 lbs @ 1.180", 400 lbs @ 1.130", Coil Bind 1.070"
I see that the spring specs show range at installed height. I'd rather not decrease the amount of installed height and compress the spring to increase seat pressure because then I'm worried about the spring binding at max lift.
So based on the cam selections, 25 lbs max boost at most, and shifting at 7300 rpm, how would the springs above compare to a set that is 155 lbs @ 1.800, 436 lbs @ 1.150, Coil Bind 1.000", Max lift .700" ?
What I'm trying to better understand is that when you take boost, rpm, and the cam profile into account, what math is used to determine if the spring specs provided are adequate enough.
I hear that springs are sometimes shimmed .050-.060" of coil bind to eliminate spring surge.
LS3 intake/nw 92mm throttle body
823 heads, LS3 rockers, CHE trunnions, 11/32 .080 hardened pushrods, powder metal valve guides, Johnson 2116LSR lifters
GM Hollow Stem Intake Valves 2.165 - 12569427
GM Inconel exhaust valve upgrade 1.59 - #12612427
Spring specs are 155 lbs @ 1.780", 380 lbs @ 1.180", 400 lbs @ 1.130", Coil Bind 1.070"
FIS T6 V2 88/102 1.32 AR
I'm planning on running around 20-25lbs of boost, shift at 7300 RPM
Looking at 2 possible hydraulic cams on this new combo:
226/243 |.618"/.618" | 115 LSA +5
235/243 | .635”/.613” | LSA116.5 +6
So with rocker ratio of 1.7....
Cam #1 Intake max lift @ valve is 1.051, Exhaust max lift @ valve is 1.051 ?
Cam #2 Intake max lift @ valve is 1.080, Exhaust max lift @ valve 1.042 ?
Where I need more schooling is the how to determine if you have enough spring seat pressure. 2.165 intake valve
1.59 exhaust valve
11/32 stem area = 0.093 sq in
area of circle = pi * r^2.
intake valve size
2.165 = 3.6794 - .093 = 3.586 sq in
For 10 psi boost : 2.165" diameter intake valves, the seat pressure reduced 35.86 lbs, and @ 25 psi seat pressure is reduced to 89.65 lbs
The valve spring specs that will come with the heads are the BTR .660 SK001: 155 lbs @ 1.780", 380 lbs @ 1.180", 400 lbs @ 1.130", Coil Bind 1.070"
I see that the spring specs show range at installed height. I'd rather not decrease the amount of installed height and compress the spring to increase seat pressure because then I'm worried about the spring binding at max lift.
So based on the cam selections, 25 lbs max boost at most, and shifting at 7300 rpm, how would the springs above compare to a set that is 155 lbs @ 1.800, 436 lbs @ 1.150, Coil Bind 1.000", Max lift .700" ?
What I'm trying to better understand is that when you take boost, rpm, and the cam profile into account, what math is used to determine if the spring specs provided are adequate enough.
I hear that springs are sometimes shimmed .050-.060" of coil bind to eliminate spring surge.
Last edited by 5.7stroker; Mar 7, 2024 at 10:40 AM.
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the lift numbers advertised are with the 1.7 rockers already accounted for. if you look at the cam card itself, it will have lobe lift, usually in the 300 range.
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ill see if i can address some stuff individually
you usually want to be close to coil bind. its been a while for me, but i think optimum open height is about 030 from bind.
if you want to get into this much detail you need to check the spring height at least at several valves if not all of them. back when i used to do yee haw fancy stuff, we did every single spring individually.most heights were the same but we still checked every single valve height.
this is an experience and testing thing. there isnt really a single algorithm or formula that is used. thats why efi university and comp cams and whoever else use spintrons.
a few more pounds of seat and open pressure probably wont hurt, but that doesnt mean that more is better. back in the day we used to throw crazy seat pressure at heads and though im pretty far out of that game now, i believe the trend has gone away from that and now you will tend to see less seat pressure but more open pressure which keeps lofting under control, among other things.
as far as calculating valve area times boost, im not a believer in that being worth worrying about anymore.
im no expert so those with more modern experience please chime in.
The valve spring specs that will come with the heads are the BTR .660 SK001: 155 lbs @ 1.780", 380 lbs @ 1.180", 400 lbs @ 1.130", Coil Bind 1.070"
I see that the spring specs show range at installed height. I'd rather not decrease the amount of installed height and compress the spring to increase seat pressure because then I'm worried about the spring binding at max lift.
I see that the spring specs show range at installed height. I'd rather not decrease the amount of installed height and compress the spring to increase seat pressure because then I'm worried about the spring binding at max lift.
you usually want to be close to coil bind. its been a while for me, but i think optimum open height is about 030 from bind.
So based on the cam selections, 25 lbs max boost at most, and shifting at 7300 rpm, how would the springs above compare to a set that is 155 lbs @ 1.800, 436 lbs @ 1.150, Coil Bind 1.000", Max lift .700" ?
What I'm trying to better understand is that when you take boost, rpm, and the cam profile into account, what math is used to determine if the spring specs provided are adequate enough.
I hear that springs are sometimes shimmed .050-.060" of coil bind to eliminate spring surge.
I hear that springs are sometimes shimmed .050-.060" of coil bind to eliminate spring surge.
a few more pounds of seat and open pressure probably wont hurt, but that doesnt mean that more is better. back in the day we used to throw crazy seat pressure at heads and though im pretty far out of that game now, i believe the trend has gone away from that and now you will tend to see less seat pressure but more open pressure which keeps lofting under control, among other things.
as far as calculating valve area times boost, im not a believer in that being worth worrying about anymore.
im no expert so those with more modern experience please chime in.
Last edited by TrendSetter; Mar 7, 2024 at 12:26 PM. Reason: more better grammer
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Joined: Jul 2007
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Likes: 332
From: Wilmington, De
The weight of the valve, the retainer, the keepers, the rocker, and the spring all play a role. The less those components weigh, the less pressure that is needed to control said components.
Ultimately the only way to know for sure is to do spintron testing.
Not many can afford that, so copying someone else’s specs and double checking on a dyno for power fall off is it.
a good cam designer will know what spring should get it done as well.
Not many can afford that, so copying someone else’s specs and double checking on a dyno for power fall off is it.
a good cam designer will know what spring should get it done as well.
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Joined: Nov 2016
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From: switzerland
"as far as calculating valve area times boost, im not a believer in that being worth worrying about anymore. im no expert so those with more modern experience please chime in."
yes, just consider when the intake valve opens and what pressure it might be seeing at that instant.
btw, spring pressue is just one aspect. the design/geometric set up of the whole valvetrain is as important. look at a valve spring in slow motion. minimizing these crazy oscillation is a hard job.
yes, just consider when the intake valve opens and what pressure it might be seeing at that instant.
btw, spring pressue is just one aspect. the design/geometric set up of the whole valvetrain is as important. look at a valve spring in slow motion. minimizing these crazy oscillation is a hard job.
