Valve spring tech
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==Overview== | ==Overview== | ||
| − | This article will | + | This article will help the reader to get a grasp on the different aspects of setting up a valve spring for a particular application. |
| − | == | + | ==Valve spring design== |
| + | |||
| + | ===Beehive=== | ||
| + | ;From [http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/viewall.html David Vizard]: | ||
| + | <blockquote> | ||
| + | With gains from conventional materials at a near standstill, the other option spring specialists had was to look at spring design to see if there was a better alternative to the parallel-wound conventional spring. Turns out there was, and during the mid 1980s GM began research on the application of a design known as the "beehive" spring. As its name suggests, this spring is wound in a beehive form. With each coil getting progressively smaller, this spring has no clear-cut resonant frequency. As soon as it starts to resonate at a particular frequency, the resonant frequency changes. Result: Spring surge is, in almost all applications, reduced to levels bordering on insignificant.</blockquote> | ||
| + | [[File:Beehive vs conventional.jpg|right|350px]] | ||
| + | <blockquote> | ||
| + | The beauty of the beehive spring is that it uses its delivered force far more effectively than a conventional parallel-wound spring. It needs far less of its delivered force to control its own motion, so this leaves more to control the valvetrain. This means less overall valve-spring loads while delivering more rpm. Our spin tests on a street roller cam showed an rpm increase from 5,950 to 6,900. This was achieved with a beehive spring (Comp Cams p/n 26918) with 8 lbs. less on the seat and 20 less over the nose than its parallel-wound counterpart. Because of the propensity of hydraulic roller lifters to collapse easier than their flat counterparts, beehive springs are well-suited to hydraulic rollers. Reduced loads and better control pay off in terms of added output and rpm. The two occasions tests were run, both in small-block Fords (302 and 392 based on a 351W), showed about a 6 hp gain in each, but considering just the change in peak hp is only a small part of the story. Take a look at the graph showing the before and after tests of the beehive spring (right). What you see here is a valvetrain that retains control to significantly higher rpm. The regular spring, in spite of being stronger, hit valvetrain crash at a shade over 6,000 rpm, but it was progressively losing control (or collapsing the lifter, or a combination of both) at 5,700 rpm. The beehive spring kept it all together up to about 6,600, although power figures were only recorded to 6,400. At 6,000 rpm the beehive's ability to deliver superior control netted an increase of some '''65 hp'''. | ||
| + | </blockquote> | ||
| + | |||
| + | ====LS7 valve spring specs==== | ||
| + | ;AC Delco p/n HL-124; GM p/n 12499425 | ||
| + | *2.313" free length | ||
| + | *1.960" installed height | ||
| + | *101 lb. @ 1.960" seat pressure | ||
| + | *310 lb. @ 1.370" open pressure | ||
| + | *1.085" coil bind | ||
| + | *354 lb/in. rate | ||
| + | |||
| + | ==Choosing valve springs== | ||
| + | ;From Crane<nowiki>:</nowiki> | ||
| + | <blockquote> | ||
| + | With the many choices of aftermarket cylinder heads, most with longer-than-stock length valves, the recommendation of a specific spring for a specific cam is almost impossible. It is now necessary to select the spring that will best fit the cylinder head configuration. We offer the following as general guidelines only: | ||
| + | #Flat tappet street and street/strip '''seat''' pressures: | ||
| + | ##Small Block: 105-125# seat pressure | ||
| + | ##Big Block: 115-130# seat pressure. Big block applications need higher seat pressures due to their larger, heavier valves. | ||
| + | #Flat tappet street and street/strip '''open''' pressures: | ||
| + | ##Open pressures should not exceed 330# open pressure (sustained after spring break-in for acceptable cam and lifter life. | ||
| + | ##Open pressures should be a minimum of 220# for applications up to 4000 RPM. | ||
| + | ##For good performance above 4000, open pressures should be at least 260# with stock weight valves. Lightweight valves require less open spring pressure. | ||
| + | ##Open spring pressures over 280# can cause pressed-in studs to come loose. Therefore, we recommend screw-in studs for open pressures above 280#. | ||
| + | #Hydraulic roller cams require higher seat pressures to control the heavier roller tappets and the more aggressive opening and closing rates available to roller cam profiles. | ||
| + | ##Small block applications: 120-145# seat pressure | ||
| + | ##Big block applications: 130-165# seat pressure | ||
| + | #Hydraulic roller cams require higher open pressures to control the high vertical opening inertia of the heavier roller lifters. | ||
| + | ##Small block applications need at least 260# for general performance applications up to 4000 RPM. | ||
| + | ##Moderate performance small block applications like 300-360# open spring pressure. | ||
| + | ##Serious small block applications can tolerate 400-425#* open pressures and still expect reasonable valve train life when top quality springs, pushrods, and lubricants are used. | ||
| + | ##Big Block applications need at least 280# for general performance applications up to 4000 RPM. | ||
| + | ##Moderate performance big block applications like 325-375# open spring pressure. | ||
| + | ##Serious big block performance applications can tolerate 450#* open pressure and still expect reasonable valve train life when top quality springs, pushrods, and lubricants are used.<br>Note: Open pressures in excess of 360# require the use of roller tappet bodies made of billet steel. Crane hydraulic roller and solid roller tappets are made from heat treated steel billet to withstand the stresses of high-performance use. Most stock hydraulic roller tappet bodies are made of cast iron and cannot tolerate high spring loads.<br> | ||
| + | #Mechanical roller cam and lifters are generally used in serious street/strip and full competition applications. Mostly not used in daily drivers where day-in/day-out reliability is necessary. Instead, solid roller cams are intended for maximum performance/competition. Generally these cams are designed with very aggressive opening and closing rates. High seat pressures are necessary to keep the valves from bouncing when they come back to the seat. The high spring pressures require the use of high strength, one-piece valves. However, Crane does offer the SR-Series of Street Roller camshafts intended for daily usage.<br> | ||
| + | ##Seat pressure is determined by valve/retainer weight, engine RPM and life expectancy of components before replacement is required. <br> | ||
| + | ###Milder roller cams require 165# on the seat as an absolute minimum. <br> | ||
| + | ###180-200# is common for most modest performance applications. <br> | ||
| + | ###220-250# is common for most serious sport categories and some circle track professional categories. <br> | ||
| + | ###Pro-Stock and Blown Alcohol/Fuel drag applications use as much as 340-500# on the seat.<br> | ||
| + | ##Open pressure need to be high enough to control the valvetrain as the lifter goes over the nose of the cam. Ideally, the minimum amount of open pressure to eliminate or minimize valvetrain separation is desired. Any excess open pressure only contributes to pushrod flex, which can aggravate valvetrain separation. For serious racing applications this can be determined only by experimentation and track testing. For general guidelines we offer the following:<br> | ||
| + | ###Street/strip performance with long cam/lifter life desirable, 350-450# open. | ||
| + | ###Circle track and moderate bracket racing 450-600# open. | ||
| + | ###Serious drag racing and limited distance circle track racing 600# and up. | ||
| + | |||
| + | ==Valve spring rate== | ||
| + | ;From Crane<nowiki>:</nowiki> | ||
| + | <blockquote> | ||
| + | The rate of a spring is the force necessary to compress (or deflect) the spring | ||
| + | a specified distance. For example, if we say that a spring has a rate of 250 lbs. | ||
| + | per inch (250 #/in.), it will take 250 pounds of force to compress the spring | ||
| + | 1 inch. Fortunately, valve springs are coil springs, and coil springs are easy to | ||
| + | understand because they have an almost linear spring rate. In other words, if it takes 400 lbs. to compress a spring 1 inch, it only takes 100 lbs. to compress the spring 0.250 in., 200 lbs. to compress it 0.500 in., and 300 lbs. to compress it 0.750 in. Some people refer to spring rate as “stiffness”, and it is the understanding of this spring characteristic that is most important in selecting and setting up springs on an automotive cylinder head. <br><br> | ||
| + | Frequently a taller, softer spring is a better choice for a performance application | ||
| + | than a short, stiff spring.<br><br> | ||
| + | Consider the following possibility: | ||
| + | A vehicle owner wants to use a 0.520" valve lift camshaft in an application | ||
| + | and is considering different valve springs.<br> | ||
| + | Spring A has an installed pressure of 125# at 1.750" installed height and has | ||
| + | a rate of 280#/in.<br> | ||
| + | Spring B has an installed pressure of 115# at 1.750" installed height with a | ||
| + | rate of 410#/in.<br> | ||
| + | At 0.520" lift, Spring A has an open pressure of 271# (this is 125# of seat pressure | ||
| + | plus [0.520" x 280#/in] = 146# from spring compression). At 0.520" lift, | ||
| + | Spring B has an open pressure of 328# (this is 115# of seat pressure plus | ||
| + | [0.520" x 410#/in] = 213# from spring compression). Both of these springs would work on a street performance application requiring good performance and reliability. However, Spring A with a lower open pressure of 271# could probably be used on a cylinder head with pressed in rocker studs; while Spring B would definitely require screw in studs for adequate reliability. Spring B would probably provide better performance above 6000 RPM (especially with relatively heavy valves) because of its higher open pressure of 328#. Spring A would probably idle a little smoother with higher vacuum, especially if a high pressure oil pump or thicker oil is used. This is | ||
| + | a result of Spring A's higher seat pressure of 125#.<br><br> | ||
| + | As you can see from the example above, there are often different springs that can offer different benefits on the same cam profile. Spring A offers good performance over a wide RPM range at a lower total valvetrain cost (this assumes that the | ||
| + | heads were not machined for screw in studs). Spring B offers the possibility of somewhat improved performance beyond 6000 RPM. The vehicle owner needs to decide what he wants from his vehicle and what he wants to spend.<br><br> | ||
| + | In all-out racing, we frequently see the need for different springs on the same lobe profile depending on the anticipated RPM range. Frequently, circle track racers will run two different tracks with the same engine but with different rear end gearing. Often there can be as much as 500-700 RPM difference in the top end engine speed between the two tracks. It is not uncommon to find that the car runs better on the track with the lower peak RPM using a spring with a lower seat pressure and softer rate. At the track where the engine runs to the higher speed, the engine needs more seat pressure and a stiffer spring rate. Every combination of engine, chassis, and track is different. Significant performance improvements can often be achieved by experimenting with valve springs. If you aren’t paying attention to your springs, the guy winning most of the races probably is! | ||
| + | </blockquote> | ||
| + | |||
| + | ==Measuring valve spring installed height== | ||
| + | The correct installed height is important to prevent coil bind and to have the correct clearance between the valve guide boss/seal and the valve spring retainer. | ||
| + | |||
| + | ===Using an installed height micrometer=== | ||
[[File:PRO-66902.jpg|right]] | [[File:PRO-66902.jpg|right]] | ||
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[[File:Snap height.jpg|right]] | [[File:Snap height.jpg|right]] | ||
| − | ==Using a snap gauge== | + | ===Using a snap gauge=== |
Put a valve in the head, install the retainer and locks that will be used. Holding the valve tightly against the seat, use the snap gauge to measure the available installed height. | Put a valve in the head, install the retainer and locks that will be used. Holding the valve tightly against the seat, use the snap gauge to measure the available installed height. | ||
| − | Once the available height is known, compare that to the valve spring installed height that is required to get the seat/open pressures needed for the cam to be used. | + | Once the available height is known, compare that to the valve spring installed height that is required to get the seat/open pressures needed for the cam to be used.<br style="clear:both"/> |
| − | <br style="clear:both"/> | + | |
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| − | + | ===Measuring without snap gauge or height mic=== | |
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| − | ==Measuring | + | |
#A 6" to 8" length of small diameter welding rod or clothes hanger wire | #A 6" to 8" length of small diameter welding rod or clothes hanger wire | ||
#Wire cutters | #Wire cutters | ||
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#Needle-nose pliers | #Needle-nose pliers | ||
| − | + | ;Procedure | |
*Using the installed height of the outer spring given with the springs, cut a piece of welding rod or clothes hanger wire to that length. Round both ends of the wire on a grinder, or with a hand-held file. | *Using the installed height of the outer spring given with the springs, cut a piece of welding rod or clothes hanger wire to that length. Round both ends of the wire on a grinder, or with a hand-held file. | ||
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*If the clearance is insufficient, different retainers or keepers (available in +0.050" size) can be used to correct it, or you can cut the valve guide bosses to correct the issue. An alternative is to use longer valves, just remember that using longer valves will alter the installed height of the valve spring. Most valves are available with stems that are 0.050" or 0.100" longer than factory specification. Adjust your shim thickness accordingly. | *If the clearance is insufficient, different retainers or keepers (available in +0.050" size) can be used to correct it, or you can cut the valve guide bosses to correct the issue. An alternative is to use longer valves, just remember that using longer valves will alter the installed height of the valve spring. Most valves are available with stems that are 0.050" or 0.100" longer than factory specification. Adjust your shim thickness accordingly. | ||
| − | == | + | ==Correcting valve spring installed height== |
| + | If the installed height is insufficient (and depending on how much more installed height is needed), a +0.050" lock can be used. If even more installed height is needed, there may be different retainers that will give more height, or the valves may need to be replaced with longer valves. In some cases the valve spring seat can be machined deeper. Use caution/consult the manufacturer to be sure the seat can be made deeper without hitting a water jacket or port. | ||
| − | + | {{Note1}}On Vortec and other heads using self aligning rocker arms, using a +0.050" lock can cause interference between the rocker tip and the locks/retainer. Rockers contacting the locks/retainer has been encountered using a combination of c/n 906 Vortec heads, Comp Pro Magnum rockers p/n 1317, Comp retainer p/n 787, Comp spring p/n 26918, and the +0.050" locks. | |
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| − | + | Mock up the assembly and check the clearance closely. In the case there's '''''insufficient''''' installed height, there are a few options: | |
| − | + | *Use non self aligning rocker arms. Requires guide plates be installed. | |
| − | + | *Use longer valves | |
| − | + | *Use a different spring/retainer combo that uses a standard lock | |
| − | + | *If just the locks are hitting the rocker, using a shorter (lash cap compatible) lock like the Edelbrock p/n 9615 may help. This 7 degree lock is 0.050" lower than a regular lock. | |
| − | + | *{{!}}Use extreme caution if making the spring seat any deeper. | |
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| − | + | If it's found that there's '''''too much''''' installed height, there are a couple options: | |
| − | + | *Use hardened shims | |
| − | + | *Use a spring cup | |
| − | + | *Use -0.050" locks | |
| − | + | *Use "shorter" retainers | |
| − | + | ||
| − | + | A tool to help determine the effect on installed height using different retainers and/or locks is the Howards Cams [http://www.summitracing.com/parts/hrs-92010 p/n 92010], shown immediately below: | |
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| − | + | [[File:Ret height92010.jpg]] | |
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==Resources== | ==Resources== | ||
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