Valve Springs 101. Everything you wanted to know but were afraid to ask!
04-01-2001, 08:54 PM
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Valve Springs 101. Everything you wanted to know but were afraid to ask!
I've noticed many topics lately about changing cams and there's usually an "oh, by the way" question about valve springs along the lines of "will they take this much lift?" Well, there's more to it that that and what you don't know could cost you horsepower or even wreck your motor!
So I thought it would be worthwhile to talk about these often ignored but EXTREMELY important little pieces of coiled steel. Their only job is to close the valve once the cam is done lifting it. That's it. Pretty simple, right? Hold on. Not so simple.
You see, the valve spring has specs, just like your cam does. You wouldn't throw in any old cam in your motor, would you? You'd reserch the cam, ask a few question of the cam grinder and figure out what works best in YOUR motor. You should do this with your valve springs, too. In fact, the cam grinders are the BEST palce to ask about valve spring recommendations.
But let's talk about some real world stuff you can use. Like what's important about a valve spring's specs? The answer is multiple things:
1. Spring diameter. All factory SBC heads came with 1.25" diameter springs. The retainers are also designed for 1.25" springs and can NOT handle larger diameter springs. The spring pockets in factory heads likewise can not handle larger springs without machining them to a larger diameter. larger diameter springs can create higher pressures, in general.
2. Installed height. 99% of SBC factory cylinder heads have an instaled height of 1 23/32" (That's 1/32" shy of 1 3/4"). That's the distance from the bottom of the retainer to the bottom of the valve spring pocket when the valve is fully closed. Even heads that use a thick exhaust valve rotator type retainer are at this height, but they sink the spring pocket a little deeper to get to this same measurement.
3. Seat pressure. With the valve closed, the spring sitting at it's installed height, how much force is it applying to the valve? That's the seat pressure. And it's an AMAZING little number. Stock springs can be spec'ed for as little as 45 LBS to as high as 85! The seat pressure DIRECTLY affects how high you can rev the engine before you "float" the valves. More pressure = higher RPMs. Other factors also affect when the vavles float (cam profile) but the springs are every bit as improtant. Keep in mind that installed heigh and seat pressure go hand in hand. If your actual installed height is less than what the spring calls for your seat pressure will be higher and vice versa.
4. Maximum lift. This is determined by subtracting the height at which the spring reaches coil bind (when the coils stack flat against eachother) from the installed height. So let's say your installed height is 1.75" and the spring coil binds at 1.25". Subtracting, you find that the spring's maximum lift is .500". You better make sure you don't exceed that much lift with your cam and rocker arm ratio or you will DEFINITELY break parts!
That's a lot the keep track of. Especially when you start to mix-n-match parts. Here's how to get a handle on it:
1. Call the cam manufacturer. They will steer you in the right direction on valve spring specs. But don't expect them to have ALL the answers, especially if you are using aftermarket cylinder heads which often have different spring pickets/diameters/installed heights than stock heads!
2. What diameter? That's a function of your heads and reainers. If your heads are designed for 1.50" springs then you need retainers to match. Stock heads are 1.25" springs, like I mentioned above. Bigger diameter springs can create higher pressures than smaller ones, in general, but are not strictly necessary for most street applications.
3. Installed height. There is no substitute for measuring this yourself! Take out the valve spring, put the retianer and locks back on the valve, pull that valve fully closed by the retainer and measure as accurately as you can beteen the reatiner and the spring seat pocket (the area the spring will fit into). You can do it with a simple machinist's rule or a more expensive valve spring height mic. Either way you better be DAMNED sure of what yours is becuase it's a critical measurement! Using longer than stock valves or spring pockets that have been machined deeper than stock can affect this measurement. Aftermarket heads? God knows what their installed height is goign to be. Measure for yourself! It's CRITICAL!
4. Seat pressure. It's tied in with your installed height. A spring's seat pressure is usually expressed as lbs @ a certain installed height. Like 65 lbs @ 1.700". That's a typical stock spring spec. If your installed height is different than what the spring is spec'ed at then your seat pressure will be different from spec, too. Shorter isntalled height, higher pressure. Taller installed height, lower seat pressure. Remember that seat pressure = RPMs.
5. Maximum lift. THis is affected by installed height (see how they're all tied in with eachother?). Check your ACTUAL installed height against the coil bind height of the spring (which is usually published by the spring manufacturer on the spring spec card). A shorter installed height will lower your maximum lift capability (but increase seat pressure). A taller one will increase it (but decrease seat pressure).
WHAT TO LOOK OUT FOR IN THE REAL WORLD:
If I had a dollar for every time I saw a radical cam installed with stock springs, I'd be rich. While they may handle the lift (most stock springs can take about .500" lift) they just won't get the job done! They don't have enough SEAT PRESSURE. 65 lbs seat pressure of most stock springs is BARELY enough to get the job done with a stock cam at 5500 RPMs, let alone a high lift cam with aggressive ramps at 6000. Weak stock springs and an aggressive cam equals valve float at surprisingly low RPMs! Floating them at 4800 is not uncommon with a setup like this. SEAT PRESSURE GIVES YOU RPMs!
Here's why- valves don't float when the cam lobe "throws" the valve train off the tip of the lobe (as is often believed), it happens when the valve comes back to it's seat too fast and literally bounces off the seat! So you can see why spring seat pressure is so important. Even a mild-moderate performance cams should have at least 100 lbs seat pressure in most typical street SBC applications. Wilder cams can take more than 130. And full race cams can have seat pressures well over 200! Suddenly stock 65lb springs seem a little weak, don't they? Don't get me wrong- no need to go overboard with massive springs, but make sure you have enough to get the job done with whatever cam you are using.
Things other that the springs: So you've been a good little boy and have made sure your springs have enough seat pressure, the correct installed height and can handle your radical .525" lift cam. You're all set, right? Not so fast. You could also have interference problems with the retainers hitting the valve guides at high lift. Measure how much lift it can take before hitting. Also, if you are using popular press-on or umbrella style valve seals you better have them installed while you are taking this measurement- they both reduce the distance between the retainer and valve guide! Typical stock SBC heads using these type of seals will run out of room at about .470" valve lift due to the room the seal takes up! Be careful! Without these style seals most SBC heads can take a very large ammount of lift- over .600" usually (but your valve springs will bind long before you get there).
Last, check your rocker arm geometry. Buy a $10 Moroso rocker arm geometry checker, learn how it works and use it. Having pushrods that are too short or too long can cost you horsepower at least and can WRECK valvetrain parts at worst. Also, stock stamed steel rocker arms, even if rocker arm geometry is dead-on are all out of slot travel at about .510" maximum lift, FYI.
This is only beginning to scratch the surface of how complex valvetrains can become, but I hope it at least causes you to consider for a minute the importance of the lowly valvespring in getting what you expect out of your new cam!
[This message has been edited by Damon (edited April 01, 2001).]
So I thought it would be worthwhile to talk about these often ignored but EXTREMELY important little pieces of coiled steel. Their only job is to close the valve once the cam is done lifting it. That's it. Pretty simple, right? Hold on. Not so simple.
You see, the valve spring has specs, just like your cam does. You wouldn't throw in any old cam in your motor, would you? You'd reserch the cam, ask a few question of the cam grinder and figure out what works best in YOUR motor. You should do this with your valve springs, too. In fact, the cam grinders are the BEST palce to ask about valve spring recommendations.
But let's talk about some real world stuff you can use. Like what's important about a valve spring's specs? The answer is multiple things:
1. Spring diameter. All factory SBC heads came with 1.25" diameter springs. The retainers are also designed for 1.25" springs and can NOT handle larger diameter springs. The spring pockets in factory heads likewise can not handle larger springs without machining them to a larger diameter. larger diameter springs can create higher pressures, in general.
2. Installed height. 99% of SBC factory cylinder heads have an instaled height of 1 23/32" (That's 1/32" shy of 1 3/4"). That's the distance from the bottom of the retainer to the bottom of the valve spring pocket when the valve is fully closed. Even heads that use a thick exhaust valve rotator type retainer are at this height, but they sink the spring pocket a little deeper to get to this same measurement.
3. Seat pressure. With the valve closed, the spring sitting at it's installed height, how much force is it applying to the valve? That's the seat pressure. And it's an AMAZING little number. Stock springs can be spec'ed for as little as 45 LBS to as high as 85! The seat pressure DIRECTLY affects how high you can rev the engine before you "float" the valves. More pressure = higher RPMs. Other factors also affect when the vavles float (cam profile) but the springs are every bit as improtant. Keep in mind that installed heigh and seat pressure go hand in hand. If your actual installed height is less than what the spring calls for your seat pressure will be higher and vice versa.
4. Maximum lift. This is determined by subtracting the height at which the spring reaches coil bind (when the coils stack flat against eachother) from the installed height. So let's say your installed height is 1.75" and the spring coil binds at 1.25". Subtracting, you find that the spring's maximum lift is .500". You better make sure you don't exceed that much lift with your cam and rocker arm ratio or you will DEFINITELY break parts!
That's a lot the keep track of. Especially when you start to mix-n-match parts. Here's how to get a handle on it:
1. Call the cam manufacturer. They will steer you in the right direction on valve spring specs. But don't expect them to have ALL the answers, especially if you are using aftermarket cylinder heads which often have different spring pickets/diameters/installed heights than stock heads!
2. What diameter? That's a function of your heads and reainers. If your heads are designed for 1.50" springs then you need retainers to match. Stock heads are 1.25" springs, like I mentioned above. Bigger diameter springs can create higher pressures than smaller ones, in general, but are not strictly necessary for most street applications.
3. Installed height. There is no substitute for measuring this yourself! Take out the valve spring, put the retianer and locks back on the valve, pull that valve fully closed by the retainer and measure as accurately as you can beteen the reatiner and the spring seat pocket (the area the spring will fit into). You can do it with a simple machinist's rule or a more expensive valve spring height mic. Either way you better be DAMNED sure of what yours is becuase it's a critical measurement! Using longer than stock valves or spring pockets that have been machined deeper than stock can affect this measurement. Aftermarket heads? God knows what their installed height is goign to be. Measure for yourself! It's CRITICAL!
4. Seat pressure. It's tied in with your installed height. A spring's seat pressure is usually expressed as lbs @ a certain installed height. Like 65 lbs @ 1.700". That's a typical stock spring spec. If your installed height is different than what the spring is spec'ed at then your seat pressure will be different from spec, too. Shorter isntalled height, higher pressure. Taller installed height, lower seat pressure. Remember that seat pressure = RPMs.
5. Maximum lift. THis is affected by installed height (see how they're all tied in with eachother?). Check your ACTUAL installed height against the coil bind height of the spring (which is usually published by the spring manufacturer on the spring spec card). A shorter installed height will lower your maximum lift capability (but increase seat pressure). A taller one will increase it (but decrease seat pressure).
WHAT TO LOOK OUT FOR IN THE REAL WORLD:
If I had a dollar for every time I saw a radical cam installed with stock springs, I'd be rich. While they may handle the lift (most stock springs can take about .500" lift) they just won't get the job done! They don't have enough SEAT PRESSURE. 65 lbs seat pressure of most stock springs is BARELY enough to get the job done with a stock cam at 5500 RPMs, let alone a high lift cam with aggressive ramps at 6000. Weak stock springs and an aggressive cam equals valve float at surprisingly low RPMs! Floating them at 4800 is not uncommon with a setup like this. SEAT PRESSURE GIVES YOU RPMs!
Here's why- valves don't float when the cam lobe "throws" the valve train off the tip of the lobe (as is often believed), it happens when the valve comes back to it's seat too fast and literally bounces off the seat! So you can see why spring seat pressure is so important. Even a mild-moderate performance cams should have at least 100 lbs seat pressure in most typical street SBC applications. Wilder cams can take more than 130. And full race cams can have seat pressures well over 200! Suddenly stock 65lb springs seem a little weak, don't they? Don't get me wrong- no need to go overboard with massive springs, but make sure you have enough to get the job done with whatever cam you are using.
Things other that the springs: So you've been a good little boy and have made sure your springs have enough seat pressure, the correct installed height and can handle your radical .525" lift cam. You're all set, right? Not so fast. You could also have interference problems with the retainers hitting the valve guides at high lift. Measure how much lift it can take before hitting. Also, if you are using popular press-on or umbrella style valve seals you better have them installed while you are taking this measurement- they both reduce the distance between the retainer and valve guide! Typical stock SBC heads using these type of seals will run out of room at about .470" valve lift due to the room the seal takes up! Be careful! Without these style seals most SBC heads can take a very large ammount of lift- over .600" usually (but your valve springs will bind long before you get there).
Last, check your rocker arm geometry. Buy a $10 Moroso rocker arm geometry checker, learn how it works and use it. Having pushrods that are too short or too long can cost you horsepower at least and can WRECK valvetrain parts at worst. Also, stock stamed steel rocker arms, even if rocker arm geometry is dead-on are all out of slot travel at about .510" maximum lift, FYI.
This is only beginning to scratch the surface of how complex valvetrains can become, but I hope it at least causes you to consider for a minute the importance of the lowly valvespring in getting what you expect out of your new cam!
[This message has been edited by Damon (edited April 01, 2001).]
04-02-2001, 12:37 AM
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I was thinking the same thing.
Also near the front of all that. 45 pounds seat pressure in a V8? If you have that then it's time for new springs real fast. You'd be able to open a valve with your thumb and probably have valve float at 4000 rpm.
Never mentioned but always relivent is when switching to 1.6 rockers. The added lift of the rockers must be considered for the springs. Cam cards suggest springs for 1.5 rockers. Putting on 1.6 rockers may require different springs than what the cam manufacturer suggests.
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Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
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Best 60 foot: 1.662
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Also near the front of all that. 45 pounds seat pressure in a V8? If you have that then it's time for new springs real fast. You'd be able to open a valve with your thumb and probably have valve float at 4000 rpm.
Never mentioned but always relivent is when switching to 1.6 rockers. The added lift of the rockers must be considered for the springs. Cam cards suggest springs for 1.5 rockers. Putting on 1.6 rockers may require different springs than what the cam manufacturer suggests.
------------------
Follow my racing progress on Stephen's racing page
and check out the race car
87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season
Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662
Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association
87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley
04-02-2001, 10:29 AM
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Damn! I didnt know thats what cause valve float.. You should make that into a tech article.
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04-02-2001, 11:12 AM
#5
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Yes, believe it or not, 45 lb springs! I jsut took a set out of a set of heads from a 1978 305 2bbl motor. Put them in my valve spring tester and came up with 45lbs @ it's actual (measured) installed height of 1.718". That's exactly what the shop manual says they should be, too. Here's the scary part: the springs would have handled almost .500" of total valve lift before binding! But obviously, they wouldn't have the strength to handle even a mild performance cam- they would have floated the valves at a VERY low RPM. The motor would have "mysteriously" just had no guts over 4000 RPM. And it would have been a bear to diagnose, too. Everyone would guess inadequate fuel supply, or not enough spark advance, or lean carb jetting, or, or, or..... etc. You can almost imagine how a post like that would go on the board here, can't you?
Also, regarding the 1.6 rocker arms, yes, I probably should have gone into more detail on that since they are such a popular mod for the SBC. I only mentioned them indirectly. They DO increase maximum lift by quite a bit (for example a cam with .450" lift using 1.5 rocker arms becomes .480" lift with a set of 1.6s). Not only that, but the rate of ACCELERATION of the valve off of the seat and back down to it is also increased- requiring the valve spring work harder (may require more seat pressure).
Can you impagine a motor with stock springs, and a mild performance cam and stock rockers. The stock 65lb springs are already barely enough to get the job done at 5500, let's say. So now you add 1.6 rocker arms to help "make more top end power", but the extra workload this puts on the valve springs now casues the valves to float at only 5000! You just got LESS power by adding the higher ratio rocker arms!
Valvetrains are EXTREMELY complicated - the MOST complicated part of any engine buildup, in my opinion. Fortuantely, for most street motors just a little attention to detail can help avoid many typical rookie mistakes.
[This message has been edited by Damon (edited April 02, 2001).]
Also, regarding the 1.6 rocker arms, yes, I probably should have gone into more detail on that since they are such a popular mod for the SBC. I only mentioned them indirectly. They DO increase maximum lift by quite a bit (for example a cam with .450" lift using 1.5 rocker arms becomes .480" lift with a set of 1.6s). Not only that, but the rate of ACCELERATION of the valve off of the seat and back down to it is also increased- requiring the valve spring work harder (may require more seat pressure).
Can you impagine a motor with stock springs, and a mild performance cam and stock rockers. The stock 65lb springs are already barely enough to get the job done at 5500, let's say. So now you add 1.6 rocker arms to help "make more top end power", but the extra workload this puts on the valve springs now casues the valves to float at only 5000! You just got LESS power by adding the higher ratio rocker arms!
Valvetrains are EXTREMELY complicated - the MOST complicated part of any engine buildup, in my opinion. Fortuantely, for most street motors just a little attention to detail can help avoid many typical rookie mistakes.
[This message has been edited by Damon (edited April 02, 2001).]
04-02-2001, 11:28 AM
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Good topic. I only have one suggestion. Modify your statement on number 5 to account for about .060 of space between coils before coil bind. A cam with .500 lift should be setup with springs that don't coil bind before .560 when taking installed height into account.
04-02-2001, 12:34 PM
#7
<font face="Verdana, Arial" size="2">Originally posted by jcb999:
Good topic. I only have one suggestion. Modify your statement on number 5 to account for about .060 of space between coils before coil bind. A cam with .500 lift should be setup with springs that don't coil bind before .560 when taking installed height into account. </font>
Good topic. I only have one suggestion. Modify your statement on number 5 to account for about .060 of space between coils before coil bind. A cam with .500 lift should be setup with springs that don't coil bind before .560 when taking installed height into account. </font>
Good post, and good information. There is this and a LOT more about valve train dynamics and geometry, all available FREE, if you just ask Comp Cams for a product catalog, then read the Tech pages. Damon makes some excellent points, and this is one of the reasons I am always harping on doing the homework before just throwing "performance" parts at an engine. It sounds like Damon has done the homework.
Incidentally, there are "unknown" varibles like this in other areas as well, like in piston and con rod selection, crank design and balancing, suspension components, etc.
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04-02-2001, 12:56 PM
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Great list. This is why I harp on people so much about their valve springs. They are alot more important than your average hobbyist realizes. They're not glamorous or sexy, they don't glitter or make the engine sound different or any of that, but a motor sure won't run to its full potential if they're sub-par.
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04-02-2001, 03:03 PM
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Yeah, that's a good point about leaving a margin of safety with springs. You NEVER want to get any closer than about .025" from coil bind. .060" is a bit on the conservative side but definitely the larger the margin of safety, the better.
Ya know, I intended to just write a paragraph or two on this subject and look what a monster it turned into! There are just SO many things to know and they're ALL important. This post should certainly NOT be considered any more than a starting point- not the be-all end-all word on valvesprings. I mean I don't even talk about OPEN spring pressures and rocker arm geometry which are also very critical little topics. It would take many many pages to cover everything and I don't type fast enough for that!
Ya know, I intended to just write a paragraph or two on this subject and look what a monster it turned into! There are just SO many things to know and they're ALL important. This post should certainly NOT be considered any more than a starting point- not the be-all end-all word on valvesprings. I mean I don't even talk about OPEN spring pressures and rocker arm geometry which are also very critical little topics. It would take many many pages to cover everything and I don't type fast enough for that!
07-12-2002, 04:48 PM
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yep, I smell tech article. Which should include the actual replacement of the springs 
07-13-2002, 12:30 AM
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While were on the subject of valvesprings I need a solution to my problem. I have a set of 083 tpi heads with LT4 springs, the springs are 1.32 in diameter with 101# of pressure at an installed hieght of 1.78, Of course the valve spring pockets had to be enlarged to accept the springs and now there is no cup to keep the spring from walking around. I checked the installed height and it is almost perfect at 1.775. I found some .035 thick spring seats that has a locating shoulder on the inside that will work great but will also reduce my installed height. The springs coil bind at 1.22 and my valve lift will not exceed .465 so i am good there but was curious as to how much more the seat pressure will be now and if there is such a thing as too much. It is a hydraulic roller cam GM#14097395 with 1.6 rockers on the intake only.
I had thought about cutting the spring pockets .035 deeper and use the locators but am afraid of getting to close to a water jacket.
Thanks
Lonnie
I had thought about cutting the spring pockets .035 deeper and use the locators but am afraid of getting to close to a water jacket.
Thanks
Lonnie
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