Valve Spring Install Height Question
01-25-2016, 03:12 PM
#1
TECH Apprentice
Thread Starter
Valve Spring Install Height Question So I decided on a set of PSI 1511's that are on the way from BTR as I type this. They will be replacing a 12 year old set of Comp 987's (albeit only 12000 miles) that are still holding up, but are making me nervous.
My question is, what install height do you think would work best on a cam with only .569 lift (TR227)? I've read dozens of topics about this, mostly with regard to Comp 918's, but couldn't find a solid answer. I feel like they'd be ok installed at 1.800, as the seat and open load of the PSI's is greater than the 987's. Perhaps it'd be safer to install at 1.750 since I have such a low lift cam?
Sorry for rambling on, and thanks in advance for the feedback!
My question is, what install height do you think would work best on a cam with only .569 lift (TR227)? I've read dozens of topics about this, mostly with regard to Comp 918's, but couldn't find a solid answer. I feel like they'd be ok installed at 1.800, as the seat and open load of the PSI's is greater than the 987's. Perhaps it'd be safer to install at 1.750 since I have such a low lift cam?
Sorry for rambling on, and thanks in advance for the feedback!
Last edited by Tang2; 01-25-2016 at 03:13 PM. Reason: Spelling
01-26-2016, 07:00 AM
#2
I would run the numbers but I like to set them with a seat force of 135#, which may require some shimming. Also, I have not set up a GM head where they come in at 1.800, rather they come it most of the time around 1.76" stock. The seat value should be computed with required shim and then figure out the valve open clearance to coil bind.
01-26-2016, 11:12 AM
#3
TECH Apprentice
Thread Starter
I would run the numbers but I like to set them with a seat force of 135#, which may require some shimming. Also, I have not set up a GM head where they come in at 1.800, rather they come it most of the time around 1.76" stock. The seat value should be computed with required shim and then figure out the valve open clearance to coil bind.
PSI ML1511's
Brian Tooley titanium retainers
A couple packs of shims from BTR
New GM "divorced" valve seals from BTR
New keepers from BTR
Ferrea SL1080 locators (true .505 ID for stock guide)
The Ferrea locators are 0.060 thick, so if the pockets weren't machined down too much, I may be close to 1.75 without shims based on your prior results. I believe 1.74 would get me to .070 of coil bind at max lift.
01-26-2016, 03:04 PM
#4
Manufacturers generally provide a spring pressure number at 1.800" (like 135#) for comparison purposes only. That doesn't mean they should be installed at that height. It's just a standard for comparison.
The general formula for installed height is: Coil Bind + valve lift + 0.060" In your case, that equates to about 1.729".
To see what pressure that makes, you'll need a valve spring tester like this one:
If that's too much pressure for your use, use a lighter spring instead of increased install height; you'll get better harmonics and valve control.
The general formula for installed height is: Coil Bind + valve lift + 0.060" In your case, that equates to about 1.729".
To see what pressure that makes, you'll need a valve spring tester like this one:
If that's too much pressure for your use, use a lighter spring instead of increased install height; you'll get better harmonics and valve control.
01-26-2016, 08:09 PM
#5
TECH Apprentice
Thread Starter
Manufacturers generally provide a spring pressure number at 1.800" (like 135#) for comparison purposes only. That doesn't mean they should be installed at that height. It's just a standard for comparison.
The general formula for installed height is: Coil Bind + valve lift + 0.060" In your case, that equates to about 1.729".
To see what pressure that makes, you'll need a valve spring tester like this one:
If that's too much pressure for your use, use a lighter spring instead of increased install height; you'll get better harmonics and valve control.
The general formula for installed height is: Coil Bind + valve lift + 0.060" In your case, that equates to about 1.729".
To see what pressure that makes, you'll need a valve spring tester like this one:
If that's too much pressure for your use, use a lighter spring instead of increased install height; you'll get better harmonics and valve control.
01-27-2016, 08:06 AM
#6
You should buy a valve spring micrometer to get this right, especially since the heads have been machined. Then check the installed height with no shims but with the spring seat or the one piece seat/valve seal. This will give you a baseline install height. Also, make sure you measure to the correct position on the micrometer, some of the small beehive retainers will not sit on the top of the micrometer and you need to correct the measurements if this occurs.
Let's assume your baseline height is 1.795 inches. You first need to compute the spring stiffness for the PSI 1511:
(370-130)/1.8-1.175) = 384 lb/inch
Since the spring is 130 lbs force at an installed height of 1.800 and the assumed case is 1.795" you need to figure out how much of an increase to seat value occurs due to the shorter installed height which is reduced by 0.005". Multiply the difference by the spring stiffness to figure out how much difference it makes:
0.005" X 384 lb/inch = 1.92 lbs.
So the seat value at 1.795 would be 130+1.92 = 131.92 lbs.
From this you can see adding a shim of 0.005" would increase the seat value by another 1.92 lb for a seat value of 133.84 lbs.
Now your lift is 0.569" so to figure your over the nose (open valve) spring force, you again figure out the difference from the stiffness:
0.569" X 384 lb/inch = 218.5 lbs.
Adding this to the seat value with the shim provides the over the nose spring force when the valve is fully open:
218.5 lbs + 133.84 lbs = 352.34 lbs.
Your spring is also compressed to the following value using the assumed seat value of 1.795" from above:
1.795" - 0.005" (shim) - 0.569" (lift) = 1.221"
With a coil bind at 1.100" you have 0.121" of clearance to coil bind. So for this example you could add more shim to increase the seat value if you wanted to.
Hope this all makes sense. I put mine in a spread sheet to sort it out.
Let's assume your baseline height is 1.795 inches. You first need to compute the spring stiffness for the PSI 1511:
(370-130)/1.8-1.175) = 384 lb/inch
Since the spring is 130 lbs force at an installed height of 1.800 and the assumed case is 1.795" you need to figure out how much of an increase to seat value occurs due to the shorter installed height which is reduced by 0.005". Multiply the difference by the spring stiffness to figure out how much difference it makes:
0.005" X 384 lb/inch = 1.92 lbs.
So the seat value at 1.795 would be 130+1.92 = 131.92 lbs.
From this you can see adding a shim of 0.005" would increase the seat value by another 1.92 lb for a seat value of 133.84 lbs.
Now your lift is 0.569" so to figure your over the nose (open valve) spring force, you again figure out the difference from the stiffness:
0.569" X 384 lb/inch = 218.5 lbs.
Adding this to the seat value with the shim provides the over the nose spring force when the valve is fully open:
218.5 lbs + 133.84 lbs = 352.34 lbs.
Your spring is also compressed to the following value using the assumed seat value of 1.795" from above:
1.795" - 0.005" (shim) - 0.569" (lift) = 1.221"
With a coil bind at 1.100" you have 0.121" of clearance to coil bind. So for this example you could add more shim to increase the seat value if you wanted to.
Hope this all makes sense. I put mine in a spread sheet to sort it out.
01-27-2016, 01:07 PM
#7
TECH Apprentice
Thread Starter
You should buy a valve spring micrometer to get this right, especially since the heads have been machined. Then check the installed height with no shims but with the spring seat or the one piece seat/valve seal. This will give you a baseline install height. Also, make sure you measure to the correct position on the micrometer, some of the small beehive retainers will not sit on the top of the micrometer and you need to correct the measurements if this occurs.
Let's assume your baseline height is 1.795 inches. You first need to compute the spring stiffness for the PSI 1511:
(370-130)/1.8-1.175) = 384 lb/inch
Since the spring is 130 lbs force at an installed height of 1.800 and the assumed case is 1.795" you need to figure out how much of an increase to seat value occurs due to the shorter installed height which is reduced by 0.005". Multiply the difference by the spring stiffness to figure out how much difference it makes:
0.005" X 384 lb/inch = 1.92 lbs.
So the seat value at 1.795 would be 130+1.92 = 131.92 lbs.
From this you can see adding a shim of 0.005" would increase the seat value by another 1.92 lb for a seat value of 133.84 lbs.
Now your lift is 0.569" so to figure your over the nose (open valve) spring force, you again figure out the difference from the stiffness:
0.569" X 384 lb/inch = 218.5 lbs.
Adding this to the seat value with the shim provides the over the nose spring force when the valve is fully open:
218.5 lbs + 133.84 lbs = 352.34 lbs.
Your spring is also compressed to the following value using the assumed seat value of 1.795" from above:
1.795" - 0.005" (shim) - 0.569" (lift) = 1.221"
With a coil bind at 1.100" you have 0.121" of clearance to coil bind. So for this example you could add more shim to increase the seat value if you wanted to.
Hope this all makes sense. I put mine in a spread sheet to sort it out.
Let's assume your baseline height is 1.795 inches. You first need to compute the spring stiffness for the PSI 1511:
(370-130)/1.8-1.175) = 384 lb/inch
Since the spring is 130 lbs force at an installed height of 1.800 and the assumed case is 1.795" you need to figure out how much of an increase to seat value occurs due to the shorter installed height which is reduced by 0.005". Multiply the difference by the spring stiffness to figure out how much difference it makes:
0.005" X 384 lb/inch = 1.92 lbs.
So the seat value at 1.795 would be 130+1.92 = 131.92 lbs.
From this you can see adding a shim of 0.005" would increase the seat value by another 1.92 lb for a seat value of 133.84 lbs.
Now your lift is 0.569" so to figure your over the nose (open valve) spring force, you again figure out the difference from the stiffness:
0.569" X 384 lb/inch = 218.5 lbs.
Adding this to the seat value with the shim provides the over the nose spring force when the valve is fully open:
218.5 lbs + 133.84 lbs = 352.34 lbs.
Your spring is also compressed to the following value using the assumed seat value of 1.795" from above:
1.795" - 0.005" (shim) - 0.569" (lift) = 1.221"
With a coil bind at 1.100" you have 0.121" of clearance to coil bind. So for this example you could add more shim to increase the seat value if you wanted to.
Hope this all makes sense. I put mine in a spread sheet to sort it out.