Performance engine builders can choose from an array of intake and exhaust valves to choose from. With a variety of valve surfaces and materials available, it is necessary to conduct time to find the right valves that fit the purpose and application usage.
In the competitive performance world it’s not just about exhaust and intake valves that is apparent. With the advances in technology that have been made in the racing component industry, we’re now faced with an overwhelming array of options. The article below will will attempt to provide a detailed explanation of different materials and designs in order to better the current offerings of GSC racing valves.
Stainless-Steel Valves. Although stainless-steel-based valves are available in various types of alloys and grades High-performance stainless-steel valves are typically constructed of a material known as EV8 (a heavier-duty, more expensive stainless alloy) They are made of a single forging. Furthermore, some valve manufacturers offer a more durable stainless-steel formulation that has greater resistance to heat. Certain manufacturers use EV8 exclusively to make their exhaust valves however, others use it to make both intake and exhaust valves.
Premium performance stainless valves should have stellite tips that are hard (since stainless isn’t hardenable and a tip that is hardened must be welded to the stem) and stems with hard chrome plating (not flash chroming that is cheap) to minimize wear on the guide. The stems that are cut off can contribute to a small weight reduction and improve the flow characteristics. Take note that if a certain model of stainless-steel valves do not come with a hard-tip using caps for lash will be needed.
Titanium Valves. Titanium has the strongest strength-to-weight ratio among all known metal. In a non-alloyed state titanium is as tough as other steels, however it is around 45 percent lighter. In the production of automobile valves, it is alloyed with tiny amounts of different substances, including molybdenum and copper. Titanium is a difficult material to work with, since it is prone to galling if the tools aren’t sharp and hard enough, or when the material hasn’t been cooled appropriately during the process of machining.
The majority of titanium valves are manufactured using a forging process that begins with a forging, which is then machined into a their final size. Some are manufactured with a two-piece inertia welded design. Based on Xceldyne Technologies, this process is so effective that inertia welded valves are certified for having a better grain structure over a single-piece made design. The valve is CNC-machined and , in many instances, cut in the stem to make a bed that allows to allow for the inlay of a coating. After that, the valve gets moly-coated.
Certain sections of the valve are further machined , and the stem is then ground, leaving the plasma moly layer on only the intended stem area. The stem, head and keeper grooves then final-machined. Grinding of the stem is then finalized for dimensional tolerances of.0002 in .0002 in. Final precision-polishing minimizes the risk of carbon accumulation.
Three different types that are valve tips offered, including tips made of hardened steel or a tip coated with ceramic (ceramic tips can be utilized together with caps for lash) and thin-film technology , such as the plasma vapour deposition (PVD) coating.
Because titanium is a soft substance, it demands an appropriate contact surface near the stem tips, typically the lash caps are made of hardened. Xceldyne found that in valves with stem diameters of less than 5/16 inch. (7mm (or smaller), a specially-designed hard coating is applied to the stem’s end to guard it against the friction of the lash cap.
The hard, durable coating is designed to shield the titanium from friction that is caused by the cap’s lash. Other coatings like PVD treatment, Chromium Nitride treatment Chemical liquid deposition (CVD) diamond-like carbon (DLC) or a different special protective coatings can apply to tips. The hardened area at the tip stops the transfer of material or galling in between the tip cap and the cap.
The hollow titanium valves are offered with hollow stems, or head and stems that are hollow. Hollow stem designs decrease the weight of valves by around 10 percent. Hollow-head designs are a unique method that helps remove an additional 6-8 pounds of mass (depending on the size of the valve). In the course of the procedure, the inside and outside of the valve could be reinforced to create the structure needed to support it for durability and strength.
These precautions should be observed during handling and usage the titanium valves
Do not use your naked hands as fingerprint acids can alter the coating. Use gloves or spray the valve with oil prior to handling.
*Do not use lapping compounds or any other abrasive material if your valve has a PVD.
*Replace the valve seats after each rebuild in order to guarantee good valve-to-seat connection. The distance between the area of contact (valve face to seat) must be at least 1 millimeter.
*New valve seats should comprise relatively soft such as nodular iron or bronze (heat-treated up to Rockwell RC32 (or less).
Unless otherwise instructed by the valve manufacturer, always use lash caps that are hardened to seal titanium valves. Certain manufacturers offer valves with hardened tips that are friction-welded. Tips made of titanium that are not protected will swell when exposed rocker arm pressures.
When the valve made of titanium has an stellite tip and the tips are ground during valve maintenance However, it is important to be careful. It is recommended to safely remove a minimum of .015 or .020 in.
When it comes to the valve seat is concerned traditional hard or cast seats may wear grooves in the valve face, therefore it is suggested. There are other exotic metal seats available.
Titanium valves are intended for use in applications where the valve train weight has to be decreased, particularly for extended high-rpm and high-rpm applications. This is because titanium valves permit greater engine speeds and can allow for extremely aggressive camshaft profiles. However, for high temperatures (blown or turbo engines) titanium may not be the best option. Additionally, for a lot of urban applications, titanium may not be a suitable option for engines that don’t require to rev as much or which is buttoned up and not torn and maintained regularly. Also, it’s recommended to restrict titanium for naturally aspirated race engines or inlet-side forced-induction applications where weight of the valve train and long-term high-rpm usage is crucial.
Inconel Valves. Inconel is a trademark registered from Special Metals Corp., and refers to a group of superalloys made from nickel. The Inconel alloys can be described as oxidation and corrosion-resistant materials that are designed to be used in extreme temperatures. Inconel keeps its strength throughout the entire temperature range. Contrary to steel or aluminum, it doesn’t shrink as as (change dimensions) when heated to high temperatures.
Inconel alloy makeup may include manganese, carbon, silicon as well as sulfur, phosphorous nickel cobalt, chromium molybdenum, iron, aluminum titanium, boron, and copper. Copper has the highest content of the material being accounted for by nickel and the chromium.
5 “grades” in Inconel are commonly used: 600 625, 625, 690, 718, and 939. The main benefits of Inconel are its light weight and resistant to temperatures that are extreme, superior durability and resisting thermal dynamics.
Inconel valves provide a strong thermal resistance, and they are designed to withstand high-temperature use, like those used in turbocharged Supercharged, Nitrous, and turbocharged.
Nimonic 90 Valves. Nimonic is an alloy made of nickel and chromium which is a particular quality called Nimonic 90 is used by some manufacturers to create high-performance valves. Nimonic 90 is a superalloy comprised of nickel-chromium-cobalt, which offers high strength and the ability to withstand extremely high temperatures, reportedly well within the 2000degF range, without distortion. Manley says they’ve experienced the benefits in extreme applications such as nitromethane, and turbos with high boosts, such as multi-turbo tractor pull engines.
Sodium-Filled Valves. Sodium-filled valves feature stems that are precision-gun-drilled and filled with a specially formulated sodium. This results in weight reduction (the result of drilling with a gun to create hollow stems) and improved heat dispersion. There’s some controversy about the effectiveness of this heat transfer, due to the fact that heat transfer to guides can cause guide wear. However, even with the concerns, it’s fascinating to consider that Chevy LS7 engine has the sodium-filled valves for exhaust (along with intake valves made of titanium).
The hollow spaces between the stem and head of a valve that is sodium-cooled are filled to approximately 60 percent of their size with metallic sodium that melts around 206 degrees Fahrenheit. The forces of inertia that occur when the valve opens result in the sodium-based liquid to move upwards within the stem, transmitting heat to the guide for the valve and then onto the jacket of water.
Hollow-Stem Valves. Hollow-stem stainless-steel or titanium valves (no sodium-fill) feature gun-drilling to create hollow stems, strictly for weight reduction–approximately 10% as compared to a comparable solid-stem valve.
General Recommendations
For street engines that are primarily street using a stainless steel valve, a high-quality one is suggested. Titanium is the most popular choice for race-related applications, however certain engine builders who are specialized in turbocharged engines would prefer an extremely premium nickel Inconel valve. Hollow-stem valves are generally excellent for the intake, however they can be a challenge to make and inspect for flaws in the I.D. surface. A lot of upper-echelon engine builders are hesitant to use hollow valves because of their potential when it comes to endurance (NASCAR or 24 hour style) racing.
Valve made of stainless steel are used most often in mild-performance racing and street racing. Titanium is employed in situations where weight is a major factor and price is not an important issue. Inconel is a popular choice when exhaust gas temperatures are extremely high. The stainless steel (for street-performance) has superior durability features than titanium, and street racers don’t typically realize the true advantages of titanium. In racing, utilize titanium if you’re looking to shed weight…and invest a lot of money.
If your client is concerned about durability, concerns and he’s already producing the power the customer wants and running the engine as high as he’d like, make use of a stainless steel material. If he’s running nitromethane it is recommended to use an Inconel exhaust valve material would be the best option for a successful finish to in a race.
On the side that exhausts on the exhaust side, sodium-filling is the most effective method to increase the capacity to head an exhaust valve that is hollow. If standard diameter steel valves are needed, but weight limit is not required opting for an intake that is hollow and a sodium-filled exhaust certainly has the best option.
The most crucial thing is getting the mass out from the valve. The lighter the valveis, the more stiff the valve train is relative to the amount of mass it has to move. Furthermore, when the mass of the valve is reduced it is possible to reduce the force required to control a specific valve movement and/or switch to an even more powerful cam design to generate more power.
Some valve manufacturers provide only solid stem designs, hollow stems are certainly less mass. It is possible that they are the most efficient way to go but there are significant manufacturing and inspection hurdles to overcome when making hollow valves.
The issue for your client is: What is the most secure and efficient option to put my money while building this engine for this particular project within the budget? The answer may be hollow valves however, in the majority of cases it will likely be a solid stem for the valve at the very least, unless there is an enormous technological leap in the manufacturing aspect. As OEMs begin to explore more advanced technology for valve manufacturing in the mass-market side as new technologies are developed, they could become available to the aftermarket to manufacture these components on the race and performance side.
Although the majority of the market is the square groove lock, the strains within the valve are reduced by a only a single circular (radius) groove. The most stress-free system is a top design that has a tiny round groove that runs along one end of the locking. The lock is constructed with a smaller angles than the retentioner, so it is controlled by collet force that squeezes harder in the bottom of the lock-to-valve connection.
Radiused grooves solve the problem in stress zones arising with a tiny diameter of an inside of a lock with a square groove. When racing at the highest level, with valves made of any material retainers, locks and other components might only have a single groove since it forces locks to hold onto the stem of the valve, and hold it in its place. A lot of OE engines come with multiple grooves of valves and locks made of steel which allow the valve to spin inside to the lock. This is perfect for street performance and low-end. Since there is a gap between valves and the locks and the valve, it can cause an overstress issue if it’s used in racing with extreme force.
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