Doe's boost affect valve spring requirements?
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Doe's boost affect valve spring requirements?
I recently received my 315cnc afr heads and am looking for opinions on valve springs. I think my installed height is going to end up around 1.950 and i'm going to be running a hydraulic roller cam with less than .650 lift. I will be running as much as 12 psi boost and no more than 6000rpm's at wot.On my last heads(merlin vr's) i used springs i bought from tyler crockett that went in at about 180 psi seat and 420 open. I thought that seemed like WAY too much spring for a hydraulic roller cam but if you figure they drop 10% after breaking in guess it would be more like 160 seat/380 open. They are still on motor,haven't pulled it out yet for freshening but they have worked for 2 years. What are good springs to run in a application like mine,can anyone give me their first hand experince?How does boost affect valve spring requirements?I would think if a typical N/A motor needed lets say 300 psi open to keep valve from floating at 6000 rpm's and keep the roller lifter in full contact with lobe you would have to add spring pressure,at least on the intake valve,to help over come the boost trying to open valve ( 2.25 dia divided by 2=1.125 x 3.14 squared=12.48 sq " x 12 psi=149.74 pounds of opening force). Now,if that was true,people wouldn't be able to drop these prochargers and whipples on these stock gm motors and get many rpm's before valve train failure so i know it can't be a requirement but is it something that needs to be taken into consideration?Who has a good price on premium valve springs and what kinda spec's should i look for,Thanks,Smitty
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Re: Doe's boost affect valve spring requirements?
Smitty, you are correct in your assumption on more spring pressure on the intake valves. I have always been taught to increase the pressure on the intake valve 10% for every 5lbs of boost.
Chris
Chris
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Re: Doe's boost affect valve spring requirements?
I've always run 180 to 190 on the seat for hydraulic rollers with blowers and 160 to 170 on na engines and I generally run under 10 lbs of boost on pleasure boat or poker run stuff that we turn under 6000 RPM and the open press tends to be anywhere from 410 to 460 over the nose . Hope that helps you Laz Mesa
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Re: Doe's boost affect valve spring requirements?
Sort of correct.
2.25" intake valve
3/8" stem.
2.25/2=1.125 1.125 x 1.125 x 3.14 = 3.97 in.sq.
.375/2=.1875 .1875 x .1875 x 3.14 = 0.110 in.sq.
so valve face area is 3.97 - .11 = 3.86 in.sq.
12 psi on 3.86 in.sq. = 46.32 pounds of force due to intake pressure
And spring pressures are in Pounds.
not psi.
Other than that, you got the concept nailed...
2.25" intake valve
3/8" stem.
2.25/2=1.125 1.125 x 1.125 x 3.14 = 3.97 in.sq.
.375/2=.1875 .1875 x .1875 x 3.14 = 0.110 in.sq.
so valve face area is 3.97 - .11 = 3.86 in.sq.
12 psi on 3.86 in.sq. = 46.32 pounds of force due to intake pressure
And spring pressures are in Pounds.
not psi.
Other than that, you got the concept nailed...
#5
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Re: Doe's boost affect valve spring requirements?
Originally Posted by mcollinstn
Sort of correct.
2.25" intake valve
3/8" stem.
2.25/2=1.125 1.125 x 1.125 x 3.14 = 3.97 in.sq.
.375/2=.1875 .1875 x .1875 x 3.14 = 0.110 in.sq.
so valve face area is 3.97 - .11 = 3.86 in.sq.
12 psi on 3.86 in.sq. = 46.32 pounds of force due to intake pressure
And spring pressures are in Pounds.
not psi.
Other than that, you got the concept nailed...
2.25" intake valve
3/8" stem.
2.25/2=1.125 1.125 x 1.125 x 3.14 = 3.97 in.sq.
.375/2=.1875 .1875 x .1875 x 3.14 = 0.110 in.sq.
so valve face area is 3.97 - .11 = 3.86 in.sq.
12 psi on 3.86 in.sq. = 46.32 pounds of force due to intake pressure
And spring pressures are in Pounds.
not psi.
Other than that, you got the concept nailed...
#6
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Re: Doe's boost affect valve spring requirements?
Originally Posted by MESABALANCING
I've always run 180 to 190 on the seat for hydraulic rollers with blowers and 160 to 170 on na engines and I generally run under 10 lbs of boost on pleasure boat or poker run stuff that we turn under 6000 RPM and the open press tends to be anywhere from 410 to 460 over the nose . Hope that helps you Laz Mesa
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Re: Doe's boost affect valve spring requirements?
Originally Posted by MESABALANCING
I've always run 180 to 190 on the seat for hydraulic rollers with blowers and 160 to 170 on na engines and I generally run under 10 lbs of boost on pleasure boat or poker run stuff that we turn under 6000 RPM and the open press tends to be anywhere from 410 to 460 over the nose . Hope that helps you Laz Mesa
Roby
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