Author Topic: shimming valvesprings for equal pressure?  (Read 6454 times)

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plovett

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shimming valvesprings for equal pressure?
« on: August 20, 2020, 06:25:17 AM »
If you have a dual pattern cam with different max valve lifts do you shim the side with the lower valve lift to get about the same open pressure? 

Often, but not always the exhaust has more lift and so more open pressure if all else is equal.  But the intake valve is heavier so maybe you should shim the valve springs on the intake to get the open pressure higher or at least equal?  Obviously you would have more seat pressure, too. 

What about the opposite situation, with less exhaust lift?  If the intake has enough pressure and the exhaust has less, do you just leave it be since it is lighter? 

Or would you want a light side and heavy side, if both are adequate for their tasks?  That way you could swap valve springs from intake to exhaust every once in a while to possibly increase their life.

This is all assuming the distance from coil bind is in the acceptable window for both intake and exhaust.  Or is it important to optimize that distance for both?

I know so many questions.  The main one is, would you shim the side with lower lift to get the same open pressure, especially if the lower lift one is the intake?   

My current solid flat tappet cam has the same lift on both intake and exhaust even though it is a dual pattern so I kept the heights all the same.  I am currently looking at solid roller profiles, some with the same lifts for intake and exhaust and some not.

thanks for any thoughts,

pl

blykins

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Re: shimming valvesprings for equal pressure?
« Reply #1 on: August 20, 2020, 06:33:03 AM »
Depends on the degree of difference.  If it's .020-.030", even on a 500 lb/in spring, that's only 10 lbs of spring pressure difference.   Your valve springs will probably vary that much anyway.  I'd rather have the install heights all dialed in right together and more importantly, on a solid roller, I'd rather have the coil bind clearances all right in there together. 

BTW, even though the intake valve is larger/heavier, I put more emphasis on the exhaust valve, not because of the valve lift, but because the exhaust valve will be the one that tags a piston if it floats.   I also put more emphasis on seat pressure rather than open pressure as that's what keeps the valves shut when they're supposed to be shut.   The open pressure is a function of how aggressive the lobe is.
« Last Edit: August 20, 2020, 06:46:49 AM by blykins »
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plovett

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Re: shimming valvesprings for equal pressure?
« Reply #2 on: August 20, 2020, 07:35:34 AM »
Thanks!  I wonder how often completely different springs are run on the intake and exhaust.   Say if different lobe families are used.  Not applicable to me, I'm not doing anything that intense.  just wondering. 

pl

blykins

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Re: shimming valvesprings for equal pressure?
« Reply #3 on: August 20, 2020, 07:41:42 AM »
Thanks!  I wonder how often completely different springs are run on the intake and exhaust.   Say if different lobe families are used.  Not applicable to me, I'm not doing anything that intense.  just wondering. 

pl

Not uncommon.  And it's usually not because the lift is that much different, it's because the install heights are that different between intake/exhaust, or the rocker arm ratios are different.

If I vary the intake/exhaust lifts, it's usually not by much at all.   I know lots of guys like doing the cams with more exhaust duration but less exhaust lift, or similar, but I personally have never seen that big of a correlation there. 
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WConley

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Re: shimming valvesprings for equal pressure?
« Reply #4 on: August 20, 2020, 09:46:33 AM »
...  I'd rather have the coil bind clearances all right in there together.  ...



This!  You want the coil bind clearance to be relatively small (like .050") and consistent in order to prevent coil surge / loss of valve control.  I've found in my testing that damping the springs in this way is better than adding spring pressure.
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1968galaxie

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Re: shimming valvesprings for equal pressure?
« Reply #5 on: August 20, 2020, 10:18:48 AM »
This!  You want the coil bind clearance to be relatively small (like .050") and consistent in order to prevent coil surge / loss of valve control.  I've found in my testing that damping the springs in this way is better than adding spring pressure.

Tight coil bind clearance to control surge is important for solid roller high rpm applications.
For street 5500 rpm cases with mild camshaft events tight coil bind clearance is certainly not a requirement.

Falcon67

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Re: shimming valvesprings for equal pressure?
« Reply #6 on: August 20, 2020, 11:48:20 AM »
Thanks!  I wonder how often completely different springs are run on the intake and exhaust.   Say if different lobe families are used.  Not applicable to me, I'm not doing anything that intense.  just wondering. 

pl

I've never used that, never had to.  I would rely on my cam engineer to say what spring to use and supply them anyway.  I have a setup for checking the springs, but I only set up my heads to hit the recommended installed height.  Springs these days are pretty accurate in my experience.  I have a set of mild solid flat Crane springs somewhere that were on a 238/248 Crane cam with about 600 passes on them and all 16 tested spec on when stored. 

frnkeore

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Re: shimming valvesprings for equal pressure?
« Reply #7 on: August 20, 2020, 12:33:17 PM »
The way that I do it, you have to know the open spring pressure that you need first, second, you have to know your max installed spring ht available. Your limited there, to your basic valve stem length but, you can get + .050 keepers, to increase it.

With the known, net lift, subtracted from the installed ht, you look through your spring catalog, for a spring that has a spring rate, in your min pressure range and is at least .050 to no more than .100 off coil bind. .060 has always been the number that I shoot for.

The coil bind clearance, has always been the most import spec to me. It gives the most longevity, because that the area that they should be made, to work in, for best harmonics and least spring surge.

Not worry about seat pressure, just shim for coil bind clearance and make sure you have enough open pressure for your application.

Frank

blykins

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Re: shimming valvesprings for equal pressure?
« Reply #8 on: August 20, 2020, 01:01:17 PM »
Not worry about seat pressure, just shim for coil bind clearance and make sure you have enough open pressure for your application.

Frank, please clarify on what you mean here.  Because surely you can't think that seat pressure isn't critical....
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frnkeore

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Re: shimming valvesprings for equal pressure?
« Reply #9 on: August 20, 2020, 01:11:38 PM »
Brent, you can't have both low seat pressure and high open pressure. Different engineered springs, will have a little difference in closed spring pressure but, you can not have what ever you want for closed pressure and optimum open pressure for open spec cam.

My criteria, is coil bind clearance as the most important aspect.
Frank

blykins

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Re: shimming valvesprings for equal pressure?
« Reply #10 on: August 20, 2020, 01:26:44 PM »
Brent, you can't have both low seat pressure and high open pressure. Different engineered springs, will have a little difference in closed spring pressure but, you can not have what ever you want for closed pressure and optimum open pressure for open spec cam.

My criteria, is coil bind clearance as the most important aspect.

Yes, you can have low seat pressure and high open pressure.  There are conical springs that give about 150 lbs seat and 630 open. 

Yes, you can absolutely have whatever you want for closed pressure and optimum open pressure.   Very easy, actually.  With as many valve springs that are offered by Comp, Manley, PAC, PSI, Isky, etc., and with just as many ways of manipulating that, you can have whatever you want.

I'll add that seat pressure is as critical, if not more so, than open pressure.  Seat is what makes the valve return to where it's supposed to be.  I always look at seat pressure vs. install height first thing.  Open isn't as critical to me at all, and to be honest, I use a very rudimentary way of choosing what open pressure I need.  The seat pressure is chosen more carefully, based on the valve sizes, weights, cam lobe shape, rpm, etc.  If you've ever seen someone break an exhaust valve head off, you'll not question whether or not they had enough open pressure.
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My427stang

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Re: shimming valvesprings for equal pressure?
« Reply #11 on: August 20, 2020, 02:38:11 PM »
I spend quite a bit of time picking springs and agree with Brent, if you don’t manage closed pressure, you run the risk of bounce. Especially with a a heavy BBF or BBC valve

Although I do also look at open pressure, especially if I think the cam may be hard to control over the nose, what I don’t understand is the statement about not picking exactly all the parameters you want, in fact, I include coil bind in that too.  The world is your oyster, there are so many options out there, I haven’t found a situation where I couldn’t control all numbers with parts choices and installed height adjustments
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frnkeore

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Re: shimming valvesprings for equal pressure?
« Reply #12 on: August 20, 2020, 05:50:59 PM »
So then, Brent, you do not care what the coil bind clearance is, right?

You'll run a spring .25 off coil blind or .000 clearance, right? What ever it takes to have low seat pressure, right?

Conical springs produce lower valve mass and can help but, they can't negate the need for open pressure.

So, give me a example of a actual spring, for a 8K (500 over rev factor) engine, with 1.78 installed ht, and .600 net lift and we will say 150 lb seat pressure. You say you an have anything you want, right? Oh, I forgot, it needs hyd rollers so I don't have to fiddle with it. What's the spring number I want?

I'll give you a break and won't require positive rotating retainers :)

We have ran 8k engines, for many years w/o conical springs. I would say, before you were born, even. As heavy a seat pressure as you had to take, to get the open pressure and longevity needed. Coil bind has to be addressed as well as fatigue.

For a street engine at 5500 or less, seat pressure isn't as important. Low lift and low duration, with longer ramps, won't get you into any area, where your gonna pull a valve apart or shorten valve seat life, beyond normal rebuild life. You can triple spring prices with conicals. That's fine, if you don't need the money someplace else. Each part in a engine costs money, there are a LOT of parts. I make my decisions of where I spend my money and I spend it wisely.

Correct coil bind settings, will lengthen spring life as that is where they are designed to work.

To answer the PO's question:

Quote
The main one is, would you shim the side with lower lift to get the same open pressure, especially if the lower lift one is the intake?
 

You want to set them at the same coil bind clearance, for best results.
Frank

blykins

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Re: shimming valvesprings for equal pressure?
« Reply #13 on: August 20, 2020, 06:28:07 PM »
So then, Brent, you do not care what the coil bind clearance is, right?

You'll run a spring .25 off coil blind or .000 clearance, right? What ever it takes to have low seat pressure, right?

Conical springs produce lower valve mass and can help but, they can't negate the need for open pressure.

So, give me a example of a actual spring, for a 8K (500 over rev factor) engine, with 1.78 installed ht, and .600 net lift and we will say 150 lb seat pressure. You say you an have anything you want, right? Oh, I forgot, it needs hyd rollers so I don't have to fiddle with it. What's the spring number I want?

I'll give you a break and won't require positive rotating retainers :)

We have ran 8k engines, for many years w/o conical springs. I would say, before you were born, even. As heavy a seat pressure as you had to take, to get the open pressure and longevity needed. Coil bind has to be addressed as well as fatigue.

For a street engine at 5500 or less, seat pressure isn't as important. Low lift and low duration, with longer ramps, won't get you into any area, where your gonna pull a valve apart or shorten valve seat life, beyond normal rebuild life. You can triple spring prices with conicals. That's fine, if you don't need the money someplace else. Each part in a engine costs money, there are a LOT of parts. I make my decisions of where I spend my money and I spend it wisely.

Correct coil bind settings, will lengthen spring life as that is where they are designed to work.

To answer the PO's question:

Quote
The main one is, would you shim the side with lower lift to get the same open pressure, especially if the lower lift one is the intake?
 

You want to set them at the same coil bind clearance, for best results.

I'm typing this slow because I know you can't read fast.

Look up above.  Look at what I said about coil bind clearance.  Look at what WConley quoted me saying about coil bind clearance. 

Does it look like I don't care about coil bind clearance?  I routinely run .050-.060" and believe it or not, some spring manufacturers specifically want some of their springs at .100" CBC, so I do that sometimes too. 

NOT ONE engine builder looks at the open pressure only without looking at the seat pressures to make sure the valves don't float to eternity and if you think that seat pressure in a street engine at 5500 or less isn't important, you've got more to learn than what I thought.   Go build an FE with a hydraulic roller at 5500 and tell me seat pressure isn't important when you're listening to the valves float. 
« Last Edit: August 20, 2020, 08:55:34 PM by jayb »
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plovett

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Re: shimming valvesprings for equal pressure?
« Reply #14 on: August 20, 2020, 07:06:39 PM »
Seems to be some consensus that the distance to coil bind height might be the number one priority, at least on a solid roller.

Also seems to be some consensus that the other factors are important, too.   Can't optimize one measure without any consideration to the others. 

pl