articfriends

iTrader: (1)

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

cstraub

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

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

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...

articfriends

iTrader: (1)

Thanks for the math lesson Its been a few years since i used Pi to figure area!

articfriends

iTrader: (1)

Laz,is there a specific spring you use that holds up well? Do you stock these springs,can you pm me a price?,Thanks,Smitty

robyw1

I was going to say the 1-bar boost is the point you need to start concerning yourself with it over 6000 RPMs. When you crank up the boost to 30-PSI then the whole world of valvetrain geometry as you know it is out the window.

Roby

cstraub

If you think 30 psi is bad, try running a 140 psi. Takes a few pulls to get things lined out.

Chris