seat pressure
seat pressure 370 ci motor
vick jr intake/nw 90mm throttle body
dart pro 1 cnc heads
dual valve springs 1.295 140@1.800
cam is a 610/605 lift 242/238 duration 115 lsa hydro roller
91.5mm turbo
im planning on running around 20-25lbs of boost
my question is the seat pressure being 140 seems kinda on the low side.
how much seat pressure should i be running these springs at? thanks
vick jr intake/nw 90mm throttle body
dart pro 1 cnc heads
dual valve springs 1.295 140@1.800
cam is a 610/605 lift 242/238 duration 115 lsa hydro roller
91.5mm turbo
im planning on running around 20-25lbs of boost
my question is the seat pressure being 140 seems kinda on the low side.
how much seat pressure should i be running these springs at? thanks
well, area of circle = pi * r^2.
depending on how big your intake valves are and how much boost you want to run:
11/32 stem area = 0.093 sqin
intake valve size
1.90 = 2.835 - .093 = 2.742 sqin
2.00 = 3.1416 - .093 = 3.05 sqin
2.10 = 3.464 - .093 = 3.371 sqin
for 10 psi boost : 1.9" diameter intake valves the seat pressure reduced 27.4 lbs, 2.0 valves reduced 30.5 lbs....... for 2.1 diameter valves at 25 lb boost the intake seat pressure is reduced 84 lbs.
140 lbs seat pressure with no boost is in the normal range but when you factor the amount of boost you want to run with the size of the intake valve diameter it can be way too little. I believe the larger the valve, because of the increased mass of the valve, the more seat pressure you will need to control it.
depending on how big your intake valves are and how much boost you want to run:
11/32 stem area = 0.093 sqin
intake valve size
1.90 = 2.835 - .093 = 2.742 sqin
2.00 = 3.1416 - .093 = 3.05 sqin
2.10 = 3.464 - .093 = 3.371 sqin
for 10 psi boost : 1.9" diameter intake valves the seat pressure reduced 27.4 lbs, 2.0 valves reduced 30.5 lbs....... for 2.1 diameter valves at 25 lb boost the intake seat pressure is reduced 84 lbs.
140 lbs seat pressure with no boost is in the normal range but when you factor the amount of boost you want to run with the size of the intake valve diameter it can be way too little. I believe the larger the valve, because of the increased mass of the valve, the more seat pressure you will need to control it.
don't know if you didn't read my post before you posted,
or you can't do math
2" valve = pi sq inches of area = 3.1416 sq inches - the stem area of 0.093 = 3.05 sq inch.
just multiply 3 sq inches by pounds per square inch of boost = pounds of reduced seat pressure. 10 lbs boost = 30 lbs reduced seat, 20 lbs boost = 60 lbs reduced seat pressure.
16 psi boost = 48 lbs of seat pressure reduced.
so if you have a intake valve with spring set up with 140 lbs of seat pressure, under 16 psi boost the seat pressure is reduced to 92 lbs, probably not enough.
I do not know how much seat pressure you should have, all i can say it's primarily a function of valve mass and rpm, you'll need so much seat pressure to control the valve from bouncing when it seats. If nominal seat pressures advertised by most springs for non boosted applications is in the 140 lbs range, and I don't think there's any springs advertised as 100 psi or less seat pressure as a selling point, you'll probably want around 200 lbs of seat pressure.
or you can't do math
2" valve = pi sq inches of area = 3.1416 sq inches - the stem area of 0.093 = 3.05 sq inch.
just multiply 3 sq inches by pounds per square inch of boost = pounds of reduced seat pressure. 10 lbs boost = 30 lbs reduced seat, 20 lbs boost = 60 lbs reduced seat pressure.
16 psi boost = 48 lbs of seat pressure reduced.
so if you have a intake valve with spring set up with 140 lbs of seat pressure, under 16 psi boost the seat pressure is reduced to 92 lbs, probably not enough.
I do not know how much seat pressure you should have, all i can say it's primarily a function of valve mass and rpm, you'll need so much seat pressure to control the valve from bouncing when it seats. If nominal seat pressures advertised by most springs for non boosted applications is in the 140 lbs range, and I don't think there's any springs advertised as 100 psi or less seat pressure as a selling point, you'll probably want around 200 lbs of seat pressure.
Last edited by 1 FMF; Mar 31, 2008 at 09:41 PM.
bear in mind i'm no valvetrain expert,
you'll need to know what your cam lobe lift is and what rocker ratios you plan to run. That'll leave you with how much max valve lift will be, so from here you find springs that will accomodate that much lift. Springs will have some range of installed height, which corresponds to whatever seat pressure typically around 140# I think. If you can't find springs that have the seat pressure you want then you decrease the amount of installed height (so the spring is compressed a little) which will increase your seat pressure, and you decrease the amount of installed height to where it gives you your desired seat pressure. But when you do this you also have to make sure now the spring doesn't bind at max lift because you've taken away that much distance it can be compressed, and also the amount of pressure at max lift will be greater because the spring will be compressed more.
you'll need to know what your cam lobe lift is and what rocker ratios you plan to run. That'll leave you with how much max valve lift will be, so from here you find springs that will accomodate that much lift. Springs will have some range of installed height, which corresponds to whatever seat pressure typically around 140# I think. If you can't find springs that have the seat pressure you want then you decrease the amount of installed height (so the spring is compressed a little) which will increase your seat pressure, and you decrease the amount of installed height to where it gives you your desired seat pressure. But when you do this you also have to make sure now the spring doesn't bind at max lift because you've taken away that much distance it can be compressed, and also the amount of pressure at max lift will be greater because the spring will be compressed more.
370 ci motor
vick jr intake/nw 90mm throttle body
dart pro 1 cnc heads
dual valve springs 1.295 140@1.800
cam is a 610/605 lift 242/238 duration 115 lsa hydro roller
91.5mm turbo
im planning on running around 20-25lbs of boost
my question is the seat pressure being 140 seems kinda on the low side.
how much seat pressure should i be running these springs at? thanks
vick jr intake/nw 90mm throttle body
dart pro 1 cnc heads
dual valve springs 1.295 140@1.800
cam is a 610/605 lift 242/238 duration 115 lsa hydro roller
91.5mm turbo
im planning on running around 20-25lbs of boost
my question is the seat pressure being 140 seems kinda on the low side.
how much seat pressure should i be running these springs at? thanks
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well, area of circle = pi * r^2.
depending on how big your intake valves are and how much boost you want to run:
11/32 stem area = 0.093 sqin
intake valve size
1.90 = 2.835 - .093 = 2.742 sqin
2.00 = 3.1416 - .093 = 3.05 sqin
2.10 = 3.464 - .093 = 3.371 sqin
for 10 psi boost : 1.9" diameter intake valves the seat pressure reduced 27.4 lbs, 2.0 valves reduced 30.5 lbs....... for 2.1 diameter valves at 25 lb boost the intake seat pressure is reduced 84 lbs.
140 lbs seat pressure with no boost is in the normal range but when you factor the amount of boost you want to run with the size of the intake valve diameter it can be way too little. I believe the larger the valve, because of the increased mass of the valve, the more seat pressure you will need to control it.
depending on how big your intake valves are and how much boost you want to run:
11/32 stem area = 0.093 sqin
intake valve size
1.90 = 2.835 - .093 = 2.742 sqin
2.00 = 3.1416 - .093 = 3.05 sqin
2.10 = 3.464 - .093 = 3.371 sqin
for 10 psi boost : 1.9" diameter intake valves the seat pressure reduced 27.4 lbs, 2.0 valves reduced 30.5 lbs....... for 2.1 diameter valves at 25 lb boost the intake seat pressure is reduced 84 lbs.
140 lbs seat pressure with no boost is in the normal range but when you factor the amount of boost you want to run with the size of the intake valve diameter it can be way too little. I believe the larger the valve, because of the increased mass of the valve, the more seat pressure you will need to control it.
I have a 2.08 intake and 1.60 exhaust valve. Im looking to run about 20lbs of boost. I hope i dont need that much.
if this will help here is alll my info i cut and paste from dart.
9/19/2007
SBC LS CNC Cylinder Head
Aluminum
Part Number: 11071040
Comb Chambers: 68cc (6.0 liter)
Intake Valve Dia: 2.08
Intake Port volume: 250cc
Intake Port Dim: 1.065 wide x 3.245 tall
Intake Port Location: stock
Intake Gasket: OE or Fel Pro
Exh Valve Dia.: 1.600
Exh Port volume: 94cc
Exhaust Port Dim: 1.710 wide x 1.430 tall
Exh Port Location: stock
Exhaust Gasket: OE or Fel Pro 1438
Flow, Intake: 322cfm @ .600 lift
Flow, Exhaust: 240cfm @ .600 lift
Manifold: Any aftermarket LS manifold
Milling: .005=1cc
Push Rod length: standard
Push rod Guide Plate: N/A
Retainers: Titanium
Spark Plug: Autolite AR3935
Spring Locators: 1.300 O.D.
Spring Pockets: 1.350 diameter
Springs: 1.290 Beehive 120@1.800 1.295 Dual 140@1.800
Valve Length: Standard
Valve Stem Dia: 8mm
Valve Train: OE (modification required, trim off tabs on stock rocker bar) or any aftermarket system
Valve Guides: .439 O.D.
Valve Guide length: 2.100
Valve Guide clearance: .0015-.002
Valve Guide Spacing: Standard
Valve Seats: Ductile Iron
Valve Seat dim: Intake 2.160 O.D. .350 deep Exhaust 1.650 O.D. .350 deep
Valve Seat angles: Intake 32°-45°-60°-70° Exhaust 37°-45°-radius
Stud Girdle: N/A
Torque: OE specs.
Weight: 23lbs. Bare 26lbs. Assembled
Block Use: LS style
Last edited by bumpin_records; Apr 1, 2008 at 05:18 PM.
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Verdad Gallardo for 2.08" diameter intakes, and a 8mm stem is 0.315", the simple math is
1.04^2 * pi = 3.398 sqin - 0.078 sqin for the 8mm stem = roughly 3.320 sqin valve surface area your boost pressure will be pushing on.
3.32 in^2 * 20 lbs/in^2 = 66.4 lbs. figure at least 50 lb reduction of seat pressure.
i would certainly ask the cam/valvetrain manufacturer what their recommendation is for springs. I remember reading crane or comp doing tests with 600 or 800 lb opening pressures with hydraulic lifters with no problems, try giving them a call and see what they have for 2.08" valves and 20 lbs boost.
1.04^2 * pi = 3.398 sqin - 0.078 sqin for the 8mm stem = roughly 3.320 sqin valve surface area your boost pressure will be pushing on.
3.32 in^2 * 20 lbs/in^2 = 66.4 lbs. figure at least 50 lb reduction of seat pressure.
i would certainly ask the cam/valvetrain manufacturer what their recommendation is for springs. I remember reading crane or comp doing tests with 600 or 800 lb opening pressures with hydraulic lifters with no problems, try giving them a call and see what they have for 2.08" valves and 20 lbs boost.
