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Author Topic: Lightened valvetrain, what spring pressure?  (Read 8139 times)
JLaw
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« on: October 02, 2011, 14:57:55 pm »

Hi,

When lightening your valvetrain how do you calculate the lowest/best spring pressure that will keep everything in check at up to maximum rpm? Is there a formula?

Cheers,

John.
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Mike Lawless
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« Reply #1 on: October 02, 2011, 19:19:30 pm »

I can't say I really understand the reasoning behind the ultra light set-ups. I've heard about as many guys having difficulty with wiped out cam and lifters on those as I have heavy duty stuff.

In my mind, it's all about controlling the valve. If it's bouncing off the seat (and it is more than you think), it isn't gonna make all the power it can. As such, I go with the most spring that will fit in the space and not bind. After all, if the valve wasn't bouncing off the seat, there would be no need for valve to piston clearances much more than a few thousandths of an inch.

For our mild mannered semi daily driver, it's got stock pushrods, rockers and single springs.
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Torben Alstrup
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« Reply #2 on: October 02, 2011, 22:16:17 pm »

Hello.
There is no rule of thumb that is accurate. Only a very rough guideline. If you lighten the valve train say 30 grams comnpared to a conventional set up, you will be able to rev roughly 500 rpm higher.
On engines with agressive cams like f.i. the FK 40 series less. With more easy cams its about right.

Then, if you go into the World of Raptor cams, you can basically add another 500 rpm to the scale.

- Ligtening the valve train reduces stress on moving parts, reduces friction, hence produces less heat, and ultimately  frees up horsepower. Actually A LOT. Another benefir with less valve spring pressure is that you get way less "twisting" of the engine. With massive spring tension like tha K800s and similar, it is not unusual to get 2/10 mm. twist, or spread or what you would like to call it, of the engine. That is directly related to actual valve lift, which of course becomes less. Less lift, less real time cam duration, - less hp.
- The problems with parts wearing out prematurely is also partly due to high spring pressures, but even more parts mixed that dont mix well and also use of oil with a less than desireable additive package.

T
« Last Edit: October 02, 2011, 22:34:31 pm by Torben Alstrup » Logged
Taylor
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« Reply #3 on: October 02, 2011, 23:31:58 pm »

Hello.
There is no rule of thumb that is accurate. Only a very rough guideline. If you lighten the valve train say 30 grams comnpared to a conventional set up, you will be able to rev roughly 500 rpm higher.
On engines with agressive cams like f.i. the FK 40 series less. With more easy cams its about right.

Then, if you go into the World of Raptor cams, you can basically add another 500 rpm to the scale.

- Ligtening the valve train reduces stress on moving parts, reduces friction, hence produces less heat, and ultimately  frees up horsepower. Actually A LOT.

Another benefir with less valve spring pressure is that you get way less "twisting" of the engine. With massive spring tension like tha K800s and similar, it is not unusual to get 2/10 mm. twist, or spread or what you would like to call it, of the engine. That is directly related to actual valve lift, which of course becomes less. Less lift, less real time cam duration, - less hp.
- The problems with parts wearing out prematurely is also partly due to high spring pressures, but even more parts mixed that dont mix well and also use of oil with a less than desireable additive package.

T

Yeah but you didn't answer any of his questions.

To gain that extra RPM the spring pressure needs to stay the same.
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K-Roc
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« Reply #4 on: October 03, 2011, 02:48:59 am »

Hello.
There is no rule of thumb that is accurate. Only a very rough guideline. If you lighten the valve train say 30 grams comnpared to a conventional set up, you will be able to rev roughly 500 rpm higher.
On engines with agressive cams like f.i. the FK 40 series less. With more easy cams its about right.

Then, if you go into the World of Raptor cams, you can basically add another 500 rpm to the scale.

- Ligtening the valve train reduces stress on moving parts, reduces friction, hence produces less heat, and ultimately  frees up horsepower. Actually A LOT. Another benefir with less valve spring pressure is that you get way less "twisting" of the engine. With massive spring tension like tha K800s and similar, it is not unusual to get 2/10 mm. twist, or spread or what you would like to call it, of the engine. That is directly related to actual valve lift, which of course becomes less. Less lift, less real time cam duration, - less hp.












- The problems with parts wearing out prematurely is also partly due to high spring pressures, but even more parts mixed that dont mix well and also use of oil with a less than desireable additive package.

T




What ever force is required to compress the big spring... The spring gives back as it unloads......  :-)
« Last Edit: October 03, 2011, 02:58:09 am by K-Roc » Logged
K-Roc
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« Reply #5 on: October 03, 2011, 04:30:57 am »

This is a good read.

http://www.rehermorrison.com/blog/?p=58



K-Roc,
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Jon
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« Reply #6 on: October 03, 2011, 13:58:34 pm »

Thanks for the link K-roc.
Controlling the valves is the clue, whether one can trust a good designed constant velocity ramp cam to reduce the bouncing of the cam, or using a strong spring to settle it down is the question.
I thing I will go with both.
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Torben Alstrup
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« Reply #7 on: October 03, 2011, 22:00:54 pm »

It is apples and oranges.
This gentleman talks mainly about roller cams and next, there is no talk about lightening the valve train. There is a big difference in roller cam set ups and flat tappet set ups
As for the compressed energy thinking. Well, theoreticly hes right. IRL mmmmmhh, no. It will always take more energy to compress the spring than it can deliver back. (On a 2000 + hp engine you most likely wouldnt notice 15 hp up or down. We usually have 10-20% of that. Then 5 hp is noticeable.

But I agree fully on the part with controlling the valve. An uncontrolled valve destroys way faster than one with "too much" spring pressure.

T
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JLaw
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« Reply #8 on: October 03, 2011, 22:54:12 pm »

So from how I understand it, the way to find out which springs are best for your package requires researching info, choosing what seems the most viable to the individual and then with trial and error testing your chosen setup.

This seems to be made increasingly more complicated with the varying opinions. Does anyone have any kind of guidelines for spring pressures compared to cam profiles and/or valvetrain weight?   

Thanks for all the replys, lots of ideas to think about..
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Torben Alstrup
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« Reply #9 on: October 04, 2011, 10:22:13 am »

Youre about right. Old man Berg was a true believer in "sufficient" valve spring pressure. The Bergs were also one of the first to yell "flat cam" guard, when the oil became less suitable to our engines in general. Ill bet my lunch that high spring pressure had its role in that. But now we know what causes it. We didnt then.

People around the World has made experiences, many times the hard way as to what lives and what dont. Professional tuners too of course. They will naturally recommend "enough" pressure, so you dont get into trouble on their recommendation.

T
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Taylor
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« Reply #10 on: October 04, 2011, 11:02:58 am »

Youre about right. Old man Berg was a true believer in "sufficient" valve spring pressure. The Bergs were also one of the first to yell "flat cam" guard, when the oil became less suitable to our engines in general. Ill bet my lunch that high spring pressure had its role in that. But now we know what causes it. We didnt then.

People around the World has made experiences, many times the hard way as to what lives and what dont. Professional tuners too of course. They will naturally recommend "enough" pressure, so you dont get into trouble on their recommendation.

T
Your answers seem to have a lot of words and no information.  Either your not sure or you are holding back information.  This post is in the pure racing page so I'm pretty sure he doesn't want a street car.  From my experience,  to little spring pressure always hurts parts and horsepower much faster than a ton.  Any engine here in the states that makes power has a ton of spring pressure roller or flat tappet. 
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Udo
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« Reply #11 on: October 04, 2011, 11:36:00 am »

A lightweight valve train an less spring pressure does not stress all parts so much. A lightweight lifter for example gives you 500 rpm's more with the same spring .
All my race engines have those with K-800 springs  to be shure they can run up to 9000 if needed . something like a little insurance. also a smaller engine can make more rpm with single springs

Udo
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Torben Alstrup
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« Reply #12 on: October 05, 2011, 12:16:06 pm »

What Udo said.
Taylor, I do have some facts, but as I also stated, I/we are reluctant to share information on the thin line, because eventually someone will mix "wrong" parts. And then whos the jerk (?)

I (and others) can give you a set up that will rev 500 or 1000 rpms higher than the next. But if the recepie isnt followed, you get in trouble, fast. And I have bad experience with exactly that. Because then peoples wallets begin to make decissions that compromises what has been said.

So you are correct. Im holding back information.

T
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gbaker770
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« Reply #13 on: October 05, 2011, 17:35:39 pm »

 Roll Eyes
What Udo said.
Taylor, I do have some facts, but as I also stated, I/we are reluctant to share information on the thin line, because eventually someone will mix "wrong" parts. And then whos the jerk (?)

I (and others) can give you a set up that will rev 500 or 1000 rpms higher than the next. But if the recepie isnt followed, you get in trouble, fast. And I have bad experience with exactly that. Because then peoples wallets begin to make decissions that compromises what has been said.

So you are correct. Im holding back information.

T
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Fasterbrit
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« Reply #14 on: October 06, 2011, 10:09:49 am »

After all, if the valve wasn't bouncing off the seat, there would be no need for valve to piston clearances much more than a few thousandths of an inch.

Another huge reason for adequate piston to valve clearance is crank flex. At high rpm a crank can flex as much as 40 thou! Shocked
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Joel Mohr
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« Reply #15 on: October 06, 2011, 21:24:32 pm »

Donn at R/D spring has been doing lightweight valvetrains, and my stuff for years...My current 2442 street car combo has LS1 beehives and goes past 8,000. I also have a 1654 with FORD modular beehives that are only an inch in diameter, and it goes to 7,000. HE has formulas that work! 760-948-4698
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Airspeed
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« Reply #16 on: October 06, 2011, 21:37:24 pm »

Donn at R/D spring has been doing lightweight valvetrains, and my stuff for years...My current 2442 street car combo has LS1 beehives and goes past 8,000. I also have a 1654 with FORD modular beehives that are only an inch in diameter, and it goes to 7,000. HE has formulas that work! 760-948-4698
I can vouch for that! His bee-hives were awesome on my last n/a engine!

Did you use custom length valves or something to be able to use the LS1 beehives Joel?

Tnx,
Walter
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Joel Mohr
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« Reply #17 on: October 07, 2011, 02:29:48 am »

Yes, everything is custom....
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Fiatdude
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« Reply #18 on: October 07, 2011, 04:56:14 am »

There are SOOOO many varablies here that there isn't one good answer --- Your cam maker will have a very good idea what spring pressure is needed to make things work --- even if you run a lightened valve train, my understanding is that it really doesn't effect the amount of spring pressure needed to make everything "work" -- -- -- It just allows everything to last a little longer because it doesn't take as much HP to get it to move -- When the cam is opening the valve the spring is robbing HP from an engine, when the cam is on the back side the spring is trying its hardest to keep the valve pushrod and lifter assembly in contact with the cam. Then add in the Grind on the cam and just how hard the valve slams closed, Then add in the harmonics of this operation at a given rpm into the equation. Things get crazy very fast. -- I've read a lot of good things about the harmonic dampening abilities of the bee hive springs and will probably be calling Don in the future when I pull my K800's from my engine or I might try a set of those PSI springs coming out of NASCAR engines that a few of the big name engine builders are using
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Bruce
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« Reply #19 on: October 07, 2011, 06:17:31 am »

Is there a formula?
There is a formula.  F=ma.  However, applying it is extremely difficult.

F is the spring pressure.
m is the mass of the components being moved
a is the rate of acceleration of the components.

Here's where it gets difficult.
F is constantly changing as you compress the spring.
a is also changing, and even reversing direction!

One thing to remember when lightening your valve train is that reducing mass on the valve side is much more effective than on the pushrod side.  The reason is because your valve's acceleration rate is in many cases 1.4 times the rate of the pushrod and lifter.  Or whatever your rocker ratio is.  When you talk to the V8 guys, it's even more.  They have ratios nearing 2:1 so light valves are doubly effective.  If you are using an Engle W- series cam and stock 1.1:1 rockers, then light pushrods and lifters are almost just as effective as lightening the valve side.

Then, to make things even more difficult, your rocker ratio isn't constant!  It's always changing depending on where it is in it's travel.  I remember Mark Herbert talking about altering the rocker arm geometry from the industry accepted method by using a shorter than ideal pushrod to "lay back" the rocker.  This would increase the acceleration rate at low lift, and decrease the acceleration rate at full lift.  The idea was to gain rpms with the same spring.

On top of all that, harmonics enter into the game, further complicating the physics.
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Joel Mohr
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« Reply #20 on: October 07, 2011, 17:01:10 pm »

That's why I rely on a spring engineer.....Donn use to be part owner of S&W shock....
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