Valve spring tech
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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. | ||
| + | |||
| + | ==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> | ||
| + | |||
| + | ==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 FACED LIFTER” cam/lifter applications (Street & Street/Strip) seat pressures | ||
| + | ##Small Block: 105-125# Seat Pressure | ||
| + | ##Big Block: 115-130# Seat Pressure (Note: Big Block applications need higher seat pressures due to their larger, heavier valves.) | ||
| + | #“FLAT FACED LIFTER” Open pressures should not exceed 330# open pressure (sustained after spring break-in for accepable 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 spring open pressure.) | ||
| + | ##Spring open 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 spring 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 use higher open pressures to control the high vertical opening inertia of the heavier roller followers. | ||
| + | ##Small Block applications need at least 260# for general driving applications up to 4000 RPM. | ||
| + | ##Moderate performance small block applications like 300-360# open. | ||
| + | ##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 driving applications up to 4000 RPM. | ||
| + | ##Moderate performance big block applications like 325-375# open 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/LIFTER<br>Applications are generally for serious street/strip use and full competition. Most are not used in daily-drivers where day-to-day reliability is stressed. Instead, most of these cams are intended for winning performance. 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. In all cases, the valve action and spring pressures required mandate 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 Pressures are determined by valve/retainer weight, engine RPM and life expectancy of components before replacement is required. Milder roller cams require 165# on the seat as an absolute minimum. 180-200# is common for most modest performance applications. 220-250# is common for most serious sport categories and some circle track professional categories. Pro-Stock and Blown Alcohol/Fuel drag applications use as much as 340-500# on the seat.<br> | ||
| + | ##Open Pressures 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 more. | ||
==Resources== | ==Resources== | ||
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