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Valvetrain Feature spring means you can’t use a double spring – so there’s no backup if you break a spring (as is the case with double springs). How much spring pressure do you actually need? If you are building a mild-performance small block engine with a flat tappet cam and no more than .450˝ lift, single springs with 80 to 90 lbs. of closed seat pressure should work just fine. For a hotter street/strip engine with a flat tappet cam, single springs with 100 to 120 lbs. of closed seat pressure (300 to 330 lbs. open pressure) are usually recommended. If the engine has a roller cam with heavier lifters, you might need springs with 120 to as much as 250 lbs. of closed pressure depending on the cam grind, the weight of the valvetrain components and peak engine rpm. For a high-revving circle track or drag racing engine that is running a flat tappet cam, double springs with closed seat pressures of 130 up to 200plus lbs. may be needed to handle the rpms. Many Pro Stock drag racers are
using triple springs with up to 475 lbs. of closed seat pressure, and over 1,000 lbs. of open valve pressure. In most instances the open spring pressure will be two to three times the closed seat pressure, so the valvetrain must be strong enough to handle it. The main disadvantage with higher spring pressures (besides the load they create on the valvetrain) is that stiffer springs don’t last as long as springs with less spring tension. That might not be a big deal on a drag motor where the springs can be replaced often, but on a street car or endurance engine, short spring life would not be desirable. An important point to remember is that good quality springs are expensive. Watch out for cheap springs that seem like a bargain, but won’t hold up and will lose pressure quickly or break.
Strengthening Springs The quality of spring wire from some suppliers has increased significantly in recent years. The best springs are
made from “super clean wire” that is a high grade alloy with almost no inclusions or imperfections. When the wire is formed, it is rolled in such a way that any inclusions in its microstructure are pushed to the center of the wire. The center experiences the least stress, so the overall strength and durability of the wire is enhanced. The wire is then scanned with an electrical eddy current to reveal any hidden imperfections before it is made into a valve spring. Some spring manufacturers are also using special surface finishing procedures to extend spring life. Shot peening has long been used to create compressive residual stresses in the outer layer of the spring wire. Shot peening leaves a matte finish on the springs, while hardening the surface to help the spring handle higher loads and speeds without failing. Nitriding has a similar effect. By diffusing nitrogen into the surface of the spring, the surface is made harder and stronger. Polishing is another
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