I regret to inform you that there are not enough kocks in the world for you to suck.

 

I agree that it is curious that this issue has taken six years to surface. But recall that Stan Martin, whom I have never known to steer me wrong -- and who is completely unbiased on the subject -- stated earlier in this thread that "PS what is really strange is,is all of this info has been out for atleast 20years I have a book on forced inducetion dated in the late 70's and they tell you about the effects of PSI on the backside of the valve and give you the math to figure out how much stiffer the spring needs to be."

So I went to my favorite reference text and found this nugget:

"The force is boost pressure times the area of the intake valve. The force on a 2.2 inch diameter valve operating at 15 psi boost would be 57 pounds. If boost pressure is intended to be in the low teens, it is time to consider stiffening the intake valve springs."
Corky Bell, Supercharged!: Design, Testing, and Installation of Supercharger Systems, p. 229.

Makes sense to me. Ford gave us springs (and rods) that work fine from the factory. That does not mean that they will work well once we start monkeying with the engine.

BTW, Corky is a degreed engineer. I know him personally. If he says it, it's true.

But by all means, remain skeptical. We don't need any more sheep around here.

 

We run a P/S motor in Comp and get about 15 runs out of the frightfully expensive valve springs (close to 5k per set!!). A competitive p/s car turns about 1000rpm higher than we do now, so 3-5 runs per set of springs is probably right. Racing is just a game of who can spend money faster, and if changing springs every single run makes you faster than the p/s guys will do it. Ever hear of Greg Anderson?

By the way, this is a Serdi.

 

Good find. I can buy that, lbs/inch^2 * inch^2 = lbs.

So my intake valves are 1.84". That gives me an area of 2.66 inch^2 (3.14*radius^2). Say I'm running 20psi... that means the force on my springs is 53 lbs.

Guess the question now is how much extra force do you need to keep a valve shut when there is 53lbs of force on it? Is 54#s enough? 70? 120???

Could be argued that if you had 74#s stock to keep it shut and you added 50#s trying to open it, that you'd then need to add 50#s to the 74 to get you back to stock performance right? Probably not as straight forward as that though .

EDIT: On second thought... Using a stock valve size and stockish boost of 8psi... force would be 19#s or 74 - 19 = 55#s keeping the valve closed. Sooo to get stock like performance with larger valves and 20psi I'd need 55 + 53 = 108# springs? Sound reasonable??

 

I agree that this basic math will put you on track for the extra closed force you need for additional boost.

Does this mean you only need the extra closed force on the intake spring? That would be my guess because that is the only valve seeing the extra pressure...

You will also need a stiffer spring (higher spring rate) for more aggressive cam profiles that are available.

Assuming similar lift and acceleration curves on the cam profiles for both intake and exhaust lobes. This leads me to thinking that the exhaust spring should be similar in spring rate to the intake spring, possibly a little less considering there is less mass from a smaller valve. The preload should be higher on the intake valve over the exhaust valve, however having similar spring rates. If the same springs were used for intake as exhaust, then shimming the intake to increase the preload would reduce the available travel before coil bind. So for truely optimal performance it makes sense that two different springs should be used to give similar travel for both exhaust and intake valves before coil bind, but give the intake a higher closed force, but both valves having a similar open force which is the force needed to follow the cam profile.

 

Had another thought in addition to my basic math...

What about pressure in the cylinder??? Doesn't it want to force the valve shut? I mean if there wasn't positive pressure then exhaust would be sucked in instead of pushed out right? Wouldn't that mean a 54# spring, with the cylinder pressure behind it, would keep the valve closed even with 53# of boost force trying to open it???

Man... it's complicated... glad I'm an electical engineer, electrons are easy .

 

What everyone here is forgetting is that the CAM actually is what is closing and opening the valve.so the spring has to be strong enough to FOLLOW the profile of the cam at the RPM range that it was designed for.Look at the post I did early for why.So as the profile becomes more radicial the spring pressure has to follow since the cam is closing valve faster and has to follow the faster declining profile and................also keep in mind that as you know or should know 'a body in motion tries to stay in motion'.So as the cam is opening the valve and it reaches the max lift, that the valve will try and continue to open farther[valve and retainer,and even part of the weight of the spring itself] are stored enertia[sp]even if it is just a few oz. so the spring has to over come that too.Way more involved that what the majority of the so called engine builders think about.[not saying anything bad,they know who they are!]the key is to have enough spring to hold back these forces but not so much as to increase frictional HP losses.As well as torqutional[sp] forces on the cam.the cam is the ONLY component in the motor that will have forward AND reverse twisting at the same time.So that has to be thought of too.STan

 

69 Roadster, I think you may only be seeing part of the picture here. The main resaon for stiffer springs is to control the faster valve motion as the lifter rubs over a more aggresive cam lobe. Boost pressure is just a small reason for needing better springs.

And everyone note that there is no free lunch here, despite what anyone claims, higher spring pressures come at the expense of increased valve guide wear. This is a physical design limitation that is impossible to overcome as long as we're running engines with rockers...therfore eventual oil consumption issues will surface with stiffer springs.

*edit, looks like stan beat me to it*

 

True but what about the ones that have no PSI in them.What about the overlap?This is when BOTH intake and exhuast are open.Now what if the intake valve stayed open a few degrees longer because of the PSI lthe blower was producing?Fuel charge out the exhuast past the O2's.Giving a bad A/F ratio and down on boost because the overlap now is longer that it should be for a blower motor.The longer overlaps are for N?A engines to use the scavenging of the exhaust to help pull the burnt gases out AND suck the fuel mixture in!But with a blower you are forcing it in.So overlaps are different for and shorter for blower motors.Stan

 

Good info.

I can follow why you need a higher valve open pressure and spring rate due to the cam profile etc. That makes sense to me...

What I was trying to figure out is why you need a greater valve closed pressure. As long as the spring is pushing down more that what's pushing up it'll stay shut... or that's what is intuitive to me.

My main reason for even thinking about it in the first place what that claim that valves are staying open and we were loosing boost out our exhaust, and thus loosing power. I'm not saying it's a false claim... I'd just like to understand it before I went through the trouble changing my already-installed-and-paid-for Crower springs.

 

I didnt read every post but if it wasnt mentioned which i dont think it was you can have your springs shimmed for more seat pressure. No need for someones special springs in your case. Seems that the most anyone has pushed is 25 without blowing the heads off the damn thing. At 21 pounds of boost i think ill be fine with my comp springs shimmed. Theyre at 100lbs.

 

This sentence actually woke me up in the middle of a good sleep

Could be that Vinnies great performance with the Whipple didn't have a damn thing to do with the Whipple at all, but rather a nice set of valve springs. Since the truck will be getting a 4V soon....we will never know how the KB stacks up....I knew something was fishy here
Dale

 

Yep, I have tried to run the numbers for shimming but I can't get near 120# closed pressure and still have coil bind clearance.

Here's the specs I've come up with from reading the posts that I used for shimming and comparisons...

JDM springs (estimated)
120# @ 1.65" (VC, 1.68+.030 shim?)
260# @ 1.10" (VO, .550 lift?)
coil bind: 1.06"
Spring rate: 254 #s/inch

Crower springs
90# @ 1.640” (VC)
242# @ 1.090” (VO)
coil bind: 1.04"
Spring rate: 276 #s/inch

Does that data look correct?

 

These engines have hydraulic adjusters....when the valves get a little loose....the adjuster takes up the slack and holds the valves off the seat....this is what happens during valve float with hydraulics. This is a really bad scenario if you were running nitrous.

Buy the way, if the engine had solid lifters it would not be as sensitive to valve spring issues. The valves still wouldn't be under control but at least the valves would be able to seat eventually and the engine wouldn't show as much of a power drop off.
Dale

 

Hmmm... sounds reasonable.
What are the downsides to solid lifters? Would you have to adjust them frequently?