HIGH-PERFORMANCE BY VALVESJIM GIBSON Performance engine builders have a wide range of intake and exhaust valve choices. With so many valve materials and surface finishes available, it takes research to select valves that match the application and intended use. This photo shows a sampling of titanium valves in blank form. Stems have been machined to near-final diameter and the heads are rough-formed, prior to CNC machining. Photo courtesy Xceldyne Technologies In the serious performance community, there s more to intake and exhaust valves than meets the eye. Thanks to the technological advancements made within the racing components industry, today we have a mind-boggling array of choices. In this article, we attempt to explain various materials and designs in an effort to better understand today s valve offerings. Stainless-Steel Valves. Although stainless-steel valves may be offered in varying grades and alloy recipes, highperformance stainless-steel valves are most commonly made of material referred to as EV8 (a more expensive heavy-duty stainless alloy material), and are made from a one-piece forging. In addition, some valve makers offer a stronger stainless-steel formula that offers higher heat resistance. Some makers use EV8 only for their exhaust valves, while others utilize this material for both intake and exhaust valves. High-quality performance stainless valves should feature hard stellite tips (since stainless is not hardenable, a hardened tip must be welded onto the stem) and hard chrome-plated stems (not cheap flash chroming) to reduce guide wear. Undercut stems contribute to a slight weight reduction and benefit flow characteristics. Note: If a particular brand of stainless-steel valves does not feature a hard tip, the use of lash caps will be required. Titanium Valves. Titanium offers the highest strength-to-weight ratio of any known metal. In an unalloyed condition, titanium is as strong as some steel materials but about 45% lighter. When used to manufacture automotive valves, titanium is alloyed with small percentages of various materials, including copper and molybdenum. Titanium can be challenging to machine, as it can gall if tooling isn t hard and sharp enough, and if the material isn t cooled properly during machining. Many titanium valves are produced by starting with a forging, then machined to final shape. But some are produced using a two-piece inertia-welded design. According to Xceldyne Technologies, this process is so effective that inertia-welded valves have been certified as having a superior grain structure than a one-piece forged design. The valve is then CNC-machined and in many cases undercut in the stem area to allow a bed for the inlay of a coating. The valve is then plasma moly-coated. Specific sections of the valve are further machined and the stem is ground, leaving the plasma moly coating over only the desired stem area. The head, stem and keeper grooves are then final-machined. Stem grinding is finalized to establish dimensional tolerance to within.0002 in. A final precision-polishing reduces the potential for carbon buildup. 46 July 2011
A variety of specialty coatings can be applied to valves to enhance specific properties such as lubricity, resistance to wear and thermal performance to heads, stems or tips. Three styles of valve tips are generally available, which include a hardened steel tip or a ceramic-coated tip (ceramic tips are to be used in conjunction with lash caps) and thin-film technology such as a plasma vapor deposition (PVD) coating. Since titanium is a relatively soft material, it requires a protective contact surface at the stem tips, usually hardened lash caps. Xceldyne noted that when valves feature stem diameters smaller than 5 16 in. (7mm or less), a specialized hard coating is applied to the stem tip to protect it from lash cap friction. The durable, hard ceramic coating is intended to protect the titanium from the friction caused by the lash cap. Other coatings such as a PVD treatment, a chromium nitride treatment, chemical vapor deposition (CVD), diamond-like carbon (DLC) or other highly specialized protective application may be applied to the tips. This hardened feature at the tip prevents material transfer or galling between the tip and lash cap. Hollow titanium valves are also available, either with hollow stems or with a combination of hollow stems and hollow heads. Hollow-stem designs reduce valve weight by about Photo courtesy Xceldyne Technologies 10%. The hollow-head design is a proprietary process that removes an additional 6 to 8 grams of weight (depending on valve size). As part of the proprietary process, the inside of the valve head may be reinforced to provide a support structure for strength and rigidity. The following precautions should be taken during the handling and use of titanium valves: Do not touch the valve surface with your bare hands, since fingerprint acids may affect the coating. Use gloves or coat the valve with oil before handling. Never use a lapping compound or any abrasive material when the valve is coated with a PVD-style coating. Replace valve seats during each and every rebuild to ensure a proper valve-to-seat contact. The width of the contact zone (valve face to valve seat) should be at least 1mm. New valve seats should be a relatively soft material, such as bronze or nodular iron (heat-treated to Rockwell RC32 or less). Unless directed otherwise by the valve maker, always use hardened lash caps on titanium valves. Some makers offer valves built with friction-welded hardened tips. Bare, unprotected titanium tips will mushroom when exposed to rocker arm forces. If the titanium valve features a stellite tip, the tips can be ground during valve service, but with caution. You should be able to safely remove a maximum of approximately.015 to.020 in. As far as valve seats are concerned, traditional cast or hard seats can wear a groove into the valve face, so a nickel-bronze seat material is recommended. Other exotic-metal seats are also available. Titanium valves are designed for applications where valve train weight needs to be reduced, for high-rpm and extended high-rpm applications, since titanium valves allow for higher engine speeds and will accommodate highly aggressive camshaft profiles. However, for extreme-temperature situations (blown, turbo and nitro engines), titanium may not be the ideal choice. Also, for many street applications, titanium may not be a good choice for an engine that doesn t need to rev as highly, or for an engine that will be buttoned up and not torn down and serviced regularly. In other words, it s probably best to reserve the use of titanium for naturally aspirated race or inlet-side forcedinduction applications where valve train weight and sustained high-rpm use is paramount. Inconel Valves. Inconel is a registered trademark of Special Metals Corp., and refers to a family of nickelbased superalloys. Inconel alloys are oxidation- and corrosion-resistant materials designed for use in high-heat environments. Inconel retains strength over a wide range of operating temperatures. As opposed to steel or aluminum, it doesn t creep as much (change dimen- The Pro Stock titanium valve on the left features a PVD-applied diamond-like coating (DLC) for extreme hardness and reduction of friction. The Formula 1 titanium valve on the right features a DLC coating on the stem area for a combination of guide wear protection and friction reduction. Photos: Jim Gibson 48 July 2011
sion) under high-heat use. Inconel alloy makeup can include carbon, manganese, silicon, phosphorous, sulfur, nickel, cobalt, chromium, iron, aluminum, molybdenum, titanium, boron and copper, with the heaviest material concentration accounted for with nickel and chromium. Five grades of Inconel are in common use 600, 625, 690, 718 and 939. Basically, the benefits of Inconel include light weight, resistance to extreme temperatures, high strength and resistance to thermal dynamics. Inconel valves offer extremely high thermal resistance and are designed for high-heat use, such as found in turbocharged, supercharged and nitrous applications. Nimonic 90 Valves. Nimonic is a nickel-chromium alloy, a specific grade of which Nimonic 90 is used by some makers for producing highperformance valves. Nimonic 90 is a superalloy comprised of nickelchromium-cobalt, which offers high strength and the ability to withstand extremely high temperatures, reportedly well within the 2000 F range, without distortion. Manley reports that they ve seen success in such extreme applications as nitromethane and high-boost turbo applications such as multiple-turbo tractor-pull engines. Sodium-Filled Valves. Sodiumfilled valves feature stems that are precision-gun-drilled and filled with a specially formulated sodium. This achieves weight reduction (the result of the gun-drilling to create a hollow stem) and better heat dispersion. There is some debate about the efficiency of this heat transfer, due to concerns that the heat transfer to the guides increases guide wear. Even given these concerns, it s interesting to note that the Chevy LS7 engine features sodium-filled exhaust valves (along with titanium intake valves). The hollow spaces in the head and stem of a sodium-cooled valve are filled to about 60% of their volume with metallic sodium, which melts at about 206 F. The inertia forces that result during valve opening cause the liquid sodium to migrate upward inside the stem, transferring heat to the valve guide and subsequently to the water jacket. Hollow-Stem Valves. Hollowstem stainless-steel or titanium valves (no sodium-fill) feature gun-drilling to create hollow stems, strictly for weight reduction approximately Delphi fuel pumps. High standards. Below the surface. A B delphi.com/am They may look the same but not all parts are created equal. Delphi fuel pumps deliver fast-pressure rise for quick engine starts and feature an integrated OE fuel vapor pressure sensor and two-strainer system for long-lasting durability. What does that mean? Reliable fuel pumps you, and your customers, can trust. Providing you with the benefit of more than 100 years of OE heritage, we are the company that makes the parts cars are born with. IT S WHAT S UNDERNEATH THAT SETS DELPHI APART Delphi Fuel Module // A Integrated Fuel Pressure Regulator (1) Maintains pressure at fuel rail (2) Negates fuel return reducing vehicle EVAP emissions; B Quieter OE Turbine Pump Performance matched to OE specifi cations and lower noise levels 5 to 10 db lower in the cockpit. Circle #28 2011 Delphi Automotive Systems, LLC. All rights reserved. July 2011 49
Applying a hard coating such as titanium nitride to the stem tip and lock groove (left) protects the titanium valve material from galling damage from a lash cap and retainer locks. Coating the valve face (right) adds protection from heat and deposit buildup to that area. 10% as compared to a comparable solid-stem valve. General Recommendations For most street engines, a quality stainless-steel valve is recommended. Titanium is generally preferred for most race applications, but some engine builders that specialize in turbocharged applications prefer a highnickel Inconel valve. Hollow-stem valves tend to work great on the intake side, but are much more difficult to manufacture and to inspect for defects on the I.D. surface. Many upper-echelon engine builders shy away from hollow valves for that reason in endurance (NASCAR or 24-hour style) racing. Stainless-steel valves are most common in street and mild-performance racing. Titanium is used when valve weight is important and cost is not a consideration. Inconel is used when exhaust gas temperatures get really high. Stainless steel (for street performance) has much better durability characteristics than titanium, and the street guys won t usually see the real benefits of titanium. In racing, use titanium when you want to lose weight and spend a lot of money. If durability is your customer s concern and he s already making as much power as he wants and is already turning the engine as high as he wants, then use a stainless-steel material. If he s running nitromethane, then an Inconel exhaust valve material will be his best bet if he wants to finish a race. On the exhaust side, sodium-filling is the best way to increase the head capacity of a hollow exhaust valve. If stock diameter steel valves are re- Comp Cams www.compcams.com Performance Valve Manufacturers Milodon, Inc. www.milodon.com Crane Cams, Inc. www.cranecams.com Del West Engineering, Inc. www.delwestusa.com Electronic Chrome & Grinding www.ecgrinding.com Elgin Industries www.elginind.com Ferrea Racing Components www.ferrea.com KPMI (Kibblewhite Precision Machining) www.blackdiamondvalves.com Manley Performance Products www.manleyperformance.com Pioneer, Inc. www.pioneerautoinc.com Racing Engine Valves www.revalves.com RPM International, Inc. www.racingpartsmax.com SI Valves www.sivalves.com Supertech Performance, Inc. www.supertechperformance.com Xceldyne Technologies www.xceldyne.com Zanzi Spa www.zanzi.com 50 July 2011
quired, but a valve weight is not mandated, going to a hollow intake and sodium-filled exhaust is certainly a major advantage. The most critical point is to get mass out of the valve. The lighter the valve, the stiffer the valve train system is in relation to the mass it must move. Also, as the valve mass is decreased, you can reduce the spring force needed to control a given valve motion and/or go to a more aggressive cam design that can make more power. While some valve makers provide only solid-stem designs, the hollow stems certainly provide lower mass. Theoretically, these would be the best way to go, but there are very serious manufacturing and inspection hurdles to clear when producing a hollow valve. The question for your customer becomes: Where is the safest and best way to invest my money when building this engine for this specific application within this budget? Sometimes the answer will be a hollow valve, but in most cases it would probably be a solid valve stem, unless we see a major technical jump on the manufacturing side. As the OEMs start pursuing more exotic valve manufacturing technologies on the mass market side, new technologies may become available for the aftermarket to make these parts on the performance and racing side. While 95% of the market uses a square groove lock, the stresses in the valve are minimized with a single round (radius) groove. The lowest stress system is a top lock design with a small round groove at the top of the lock. The lock is designed with a slightly smaller angle than the retainer so the valve is held by the collet force squeezing more at the bottom region of the lock-to-valve interface. Radiused grooves address the issue of stress concentration zones associated with a very small radius of the inside corner of a square groove lock. In high-end racing with valves of any material, retainers and locks may use only a single groove because it forces the lock to grip the valve stem and hold it in place. Many OE engines feature multiple-groove steel locks and valves that allow the valve to spin in the locks, which is fine for street and low-end performance. Because there s a loose fit between the valve and locks, it could cause an overstress condition if used in severe racing. Delphi CVC compressors. High standards. Below the surface. They may look the same but not all parts are created equal. Delphi OE CVC compressors have proven warranty experience of less than 1 Incident Per Thousand Vehicles (IPTV) on major OEM applications. What does that mean? Reliable, high performance compressors you, and your customers, can trust. Providing you with the benefit of more than 100 years of OE heritage, we are the company that makes the parts cars are born with. B IT S WHAT S UNDERNEATH THAT SETS DELPHI APART Delphi CVC Compressor // A Swash Plate Variable Mechanism Patented technology adaptable to pneumatic and electronic control for high speed operation at up to 9200 RPM; B Integrated Control Valve Compact packaging and four-port fl ow design provides a wider range of control set points for improved fuel economy and emissions. Circle #29 delphi.com/am A 2011 Delphi Automotive Systems, LLC. All rights reserved. July 2011 51