Cam and Valve spring

[fredo11]

I have a question about valve spring selection. My engine is a 598cid with Big Chief heads. The cam I am using is a 288/300@50, 114ls, 810/782 gross lift. According to the cam spec card I should be using a spring(comp cam) #998. This spring sets up at 1.950@194lbs and has a spring rate of 677. The springs I have been using are a Crane spring, #99878. 2.100@238lbs, 816@1.200, spring rate of 642.
My question is, Why the huge difference between what the cam company represents and what my engine builder uses? I do not have any complaints about the performance of the engine, but trying to figure out why use a spring that is so much more than comp recommends?

[beth]

Good engine builders use springs they have experience with. Springs they have used in the past that they trust. A little extra spring pressure is a good thing, lots better than not enough. A roller cam recovers some of the parasitic spring pressure loss as the rollers push the cam along so that isn't much of an issue.

[Keith Morganstein]

The typical reason is the installed height. This is the game we all play when setting up. Getting the correct spring rate and pressures to match the installed height and the cam lobe/ rpm requirements. The cam companies aren't exaxctly stupid either. They design the lobe and know what kind of spring rate and seat pressure is needed.

The comp is the slightly stronger spring (higher rate). That is the real comparison of springs.
The pressure on the nose of the ends up being similar 758 vs. 742.

the seat pressure really isn't that far between the two for a big roller. i prefer the least seat pressure i can get away with because I don't think it helps valve and seats to slam shut any harder than needed.

Your builder did the best he could.

[Wolfplace]

for a big roller. i prefer the least seat pressure i can get away with because I don't think it helps valve and seats to slam shut any harder than needed.

Your builder did the best he could.

=
I disagree with this line of thinking.
You will not slam the valve into the seat because of too much spring pressure.
All the spring does is try to keep the parts following along with what the cam designer had in mind.
What slams the valve into the seat & or the roller into the lobe is lack of control not more of it

I agree with what Beth stated, a little more spring is a lot better than not enough & springs work both ways,,, at least in my limited opinion

[steelcomp]

for a big roller. i prefer the least seat pressure i can get away with because I don't think it helps valve and seats to slam shut any harder than needed.

Your builder did the best he could.

=
I disagree with this line of thinking.
You will not slam the valve into the seat because of too much spring pressure.
All the spring does is try to keep the parts following along with what the cam designer had in mind.
What slams the valve into the seat & or the roller into the lobe is lack of control not more of it

I agree with what Beth stated, a little more spring is a lot better than not enough & springs work both ways,,, at least in my limited opinion

I'm going to agree here, as well. Another benefit of more than less seat pressure is controlling valve bounce. Added installed ht. also allows for a few shims to be added to maintain spring pressure as the spring wears, and still have enough room for the valve lift.

[Keith Morganstein]

So what is your rule of thumb? take the cam makers specs and add how much to the seat pressure? How much to the the spring rate?

[ChrisU]

I think experience takes presidence over cam builders specs...

I'd rather over spring any day than under spring it. The roller lifters, valve seats, and keepers/retainers will thank you for it. You enter any kind of uncontrolled valve motion and it just eats up parts... seats, keepers, roller lifters...

How can a cam grinder recommend a spring? They do not know the specifics of your engine. They do not know the materials involved, the type of rockers involved, etc...

[Keith Morganstein]

I guess we all have our own ideas and experience. i try to keep an open mind though and now I'm wondering how many of the builders go heavy on the springs.

I would love to have a spintron machine at my disposal do an actual analysis of every valve train combination I work with.

I do believe the big cam companies like comp do spintron testing and computer modeling. They design the lobe profile and spec a spring to fit an application. It might not be perfect for every combo, but i believe they are pretty close.

I have a some conceptions and maybe I'm way out with them.

The spring seems so simple, but it's not. the spring has to be balanced, seat pressure and open pressure specs aren't sufficient alone for good performance. I figure, perhaps incorrectly that a spring package ( outer, innner or damper as a set etc...) will be a better choice than just picking individual springs to give a certain open/close/rate

the spring has to keep the follower on the lobe during the opening/closing event, especially on the back or closing side of the ramp. My thought is that this is where damage will occur if you don't have enough pressure or a stable enough spring to keep the lifter on the lobe. I also think that concave "quick close" lobes are particually vulnerable to spring problems.
The cam company does know the shape of the lobe and the rpm range it's designed for and should spec a spring that can work with it.

Seat pressure is just that. it's keeping the valve closed. It is not keeping the roller on the lobe because of lash clearance. The roller is basically unloaded during that event. Yes there must be enough seat pressure to keep the valve closed and not let it bounce. The studies I read indicate that too much seat pressure isn't good either. problems of spring surge arise that can also cause problems.

i try to stay close to reccomended pressures and spring package if i can. (unless I have a performance or wear indicator that I need different spring)

Of course sometimes it's not possible because of installed height and that's where the fun starts...

Till I get my spintron...LOL

[Jason G]

I have to agree with the others. Too much is better than not enough. I just had the pleasure of learning all about this the old fashioned way...making the mistake and learning from it.

Against my better judgement I used the springs that the cam manufacturer recommended. The spring recommended over the phone was significantly more than what the catalog shows for the lobe also. still not enough spring.

As Chris stated the cam folks don't necessarily have experience with various valves, stem sizes, lengths, materials, diameters, etc. (Even though they were told what I was using in this case.)

David Reher wrote an article on this subject: http://www.rehermorrison.com/techTalk/03.htm

Like just about everything in life, experience makes an "expert". If you are not sure of what spring to use, the best bet is to get in touch with someone that has "been there and done that" and get their opinion.

[Wolfplace]

I guess we all have our own ideas and experience. i try to keep an open mind though and now I'm wondering how many of the builders go heavy on the springs.

I would love to have a spintron machine at my disposal do an actual analysis of every valve train combination I work with.

I do believe the big cam companies like comp do spintron testing and computer modeling. They design the lobe profile and spec a spring to fit an application. It might not be perfect for every combo, but i believe they are pretty close.

I have a some conceptions and maybe I'm way out with them.

The spring seems so simple, but it's not. the spring has to be balanced, seat pressure and open pressure specs aren't sufficient alone for good performance. I figure, perhaps incorrectly that a spring package ( outer, innner or damper as a set etc...) will be a better choice than just picking individual springs to give a certain open/close/rate

the spring has to keep the follower on the lobe during the opening/closing event, especially on the back or closing side of the ramp. My thought is that this is where damage will occur if you don't have enough pressure or a stable enough spring to keep the lifter on the lobe. I also think that concave "quick close" lobes are particually vulnerable to spring problems.
The cam company does know the shape of the lobe and the rpm range it's designed for and should spec a spring that can work with it.

Seat pressure is just that. it's keeping the valve closed. It is not keeping the roller on the lobe because of lash clearance. The roller is basically unloaded during that event. Yes there must be enough seat pressure to keep the valve closed and not let it bounce. The studies I read indicate that too much seat pressure isn't good either. problems of spring surge arise that can also cause problems.

i try to stay close to reccomended pressures and spring package if i can. (unless I have a performance or wear indicator that I need different spring)

Of course sometimes it's not possible because of installed height and that's where the fun starts...

Till I get my spintron...LOL

=
ME.
What you said was
"for a big roller. i prefer the least seat pressure i can get away with because I don't think it helps valve and seats to slam shut any harder than needed. "
This is not the same as following the cam manufacturers recommendations.

In your last post you said:
"the spring has to keep the follower on the lobe during the opening/closing event, especially on the back or closing side of the ramp. My thought is that this is where damage will occur if you don't have enough pressure or a stable enough spring to keep the lifter on the lobe. "
And then,,
"Seat pressure is just that. it's keeping the valve closed. It is not keeping the roller on the lobe because of lash clearance. The roller is basically unloaded during that event. Yes there must be enough seat pressure to keep the valve closed and not let it bounce"

I am having trouble following you here, either the spring tries to control the complete valve train or it does not.
You can't have it both ways

I am well aware once you get to the unloaded lash condition the spring isn't doing anything except keeping the valve closed but the rest of the time it is the only thing attempting to keep the roller on the lobe & if they separate anywhere except when they are supposed to I can guarantee it will eventually beat the crap out of everything, lobe, roller, needles, valve, seat & everything in between,,

In the absence of real data like SpinTron testing, which I have no access to, or information from people I consider reliable I tend to go with the best spring I can with more rather than less pressure.

Every time we have upped the pressures we have reduced seat & lifter /lobe problems along with better looking retainers et al,,,
Going the other way would to me seem counterproductive unless I had a way to test besides in the field which tends to make for unhappy customers on occasion

But as you stated, we all have are own opinions

[Keith Morganstein]

What you said was
"for a big roller. i prefer the least seat pressure i can get away with because I don't think it helps valve and seats to slam shut any harder than needed. " This is not the same as following the cam manufacturers recommendations.

Thats what I meant, staying close to the reccomended was the least I thought I could get away with.

The big roller and my spring seat pressure statement from my first post weren't supposed to be connected. I was just saying that the two springs were actually very similar for the big roller in nose pressure.

I got a little beat on for that last sentence but that is o.k.
If I need to change to have a better valve train I will. God knows I work my butt off to do the best job possible.

I guess my thinking is kinda old fashioned in not to much seat pressure, i always stayed close to reccomended within 20lbs or so, but maybe it's time to get with the current thinking. At least I'm fortunate that I haven't had a lot of failures of beat out seats or skidding rollers. Must have been close enough to make it work.

I took some time and read the link to reher-morrison article on spring pressure. I have read many articles, but he lays it out plain and simple.

I am having trouble following you here, either the spring tries to control the complete valve train or it does not.
You can't have it both ways

Yes, the spring tries to control everything, but doesn't the spring rate help control both ends of the event?

[Darin Morgan]

Valve train design and tuning is a science all its own and has a little touch of mysticism as well. The Kinematic motion of a valve train is extremely complex. Simply stating that a spring needs "more" or "less" pressure is overly simplistic. It overlooks the finer tuning aspects of the system and especially the spring. The spring can encounter many different problems; float being just one of them. The spring can encounter Resonance, Coil surge, Float or simple Fatigue due to excessive heat or use. Float is the term most often used to describe the spring not controlling the valve train and in most cases people are correct in using this term because Float is the predominant valve train problem in most racing engines operating at moderately high engine speeds in the 7500 to 8000rpm range. This is due to either the builder not using the correct spring to control the valve train or the springs being used have fatigued with time and or heat. This is where the valves can bounces off the seat as much as .020 bleeding off the rising cylinder pressure back up the intake tract effectively shutting the engine off or keeping it from accelerating any further. Having two or three valve bounces of about .005 at the valve is a normal but albeit unhealthy occurrence in high rpm racing engines. We would like to have zero bounce, but that just doesn’t happen. Coil surge is a scenario that takes place when the spring is set up to far away from coil bind giving the middle coils room to bounce back and forth from top to bottom as the spring is closing. This usually takes place with a highly energized spring (fast ramp rate) at high engine speeds. Having a spring with not enough rate can exacerbate the problem and having a spring with both to little rate and not enough seat/nose pressure in conjunction with being set up to far from coil bind is down right deadly. I have seen springs turn blue, shatter and literally melt due to this scenario. This will cause valve bounce similar to floating the system and letting the valve hit the seat. Resonance is a killer but I find it a rare occurrence with the Super Series engines or other engines that operate at or below 7500rpm. In the big Block Chevy engine there are two distinct points within the rpm range that present a problem. 7600to 7800 and 9800-10000. 7600-7800 is usually just before the cam goes into loft (not float) and the 9800+ range is where the loft goes Bozo for a lack of a better term. The 7600-7800rpm point has been shown to excite certain types of springs that are considered to be "better" because of there increased rate and pressures. I put a set of PSI 048 style springs on a truck puller engine with the Raptor heads. I mistakenly thought that the “better " spring would lend some protection to the valve train because this guy revved the engine to 9600rpm+ and at time free revved the engine to 9500rpm+. Well he called me the after a week and said that he had broken six valve springs and the rest where Jell-O. They had lost 100lbs of seat pressure. I instantly knew to ask him one question. Do you hold the engine at or around 7600-7800rpm for any length of time? He reported that that is exactly where the engine dropped back down to when the sled came in. BINGO, resonance! I sent him A set of Comp 048 springs and told him to change them when they dropped below 285lbs. He has over 100runs on the engine and going strong. He replaces the valve springs about every 25 runs. This is the point I was trying to make. Just because a spring has more pressure or rate does not mean that it is a good match for the valve train system you are using them on. On a Drag racing engine that goes to 7600-8000 or 8500rpm on the shift, you won’t generally encounter this problem because the spring goes in and out of resonance so fast its of no consequence. If you just go to the point of resonance or just past it and back down through it, you’re generally ok. It’s when you “hang" there for any length of time that the damage becomes evident.

[ClassKing]

[quote="Darin Morgan"] "Valve train design and tuning is a science all its own and has a little touch of m-y-s-t-i-c-i-s-m as well.]

Good to hear someone of note saying this. Although the "math rules everything" guys won't like that statement.

Tip-o-the-Hat. Thanks Darrin.

[ChrisU]

I think it all comes down to trial and error which translates to experience....

Again, there is no blanket statement that you need 'this' spring for 'this' lobe.... too many variables.

[rmcomprandy]

What I have found is that cam companies will usually spec their spring requirements on the MINIMUM required side for a roller situation and on the MAXIMUM for a flat tappet.
Good judgement needs to be used in order the get what you want.

"Good judgement is learned through experience and EXPERIENCE - well, that comes from BAD judgement". -- Ben Franklin