All About The Alloys - Valve Seat Selection For High Performance Applications
When you're building a "performance" engine, what kind of valve seats should you use? That's a question for which there seems to be no definitive answer.
By Larry Carley
We can't make any sweeping generalizations about what kind of seats work best in a performance engine application because "performance" covers a lot of territory, everything from hot street engines with stainless steel valves to top fuel drag racing and NASCAR engines with titanium valves. Seat requirements vary depending on the application, what kind of valves are in the engine (stainless steel or titanium), how much money is going into the engine, and what kind of longevity the engine is expected to deliver. The valve seats in a street engine may remain in use for more miles or years than the seats in a drag engine, but they are unlikely to experience the same severity of service.
In researching this topic, we interviewed a lot of valve seat suppliers - and found that there are a number of different valve seat materials from which engine builders can choose. Many of these materials will work in a wide variety of performance applications while others are designed primarily for special applications such as industrial engines that run dry fuels like propane or natural gas. The only consensus is that different valve seat materials can be used successfully in most performance engines.
What kind of materials are we talking about? Everything from nodular/ductile iron alloys and powder metal steel seats to hard aluminum-copper and bronze alloys, and beryllium copper alloys. Many valve seat suppliers have their own proprietary alloys while others use industry standard alloys. But you don't have to be a metallurgist to appreciate the differences between some of these materials.
A valve seat must do several things. It must support and seal the valve when the valve closes, it must cool the valve, and it must resist wear and recession. Consequently, a performance valve seat material should provide a certain amount of dampening to help cushion the valve when it closes at high rpm. Very hard materials, especially on the intake side, are not the best choice here because intake valves tend to be larger, heavier and close at faster rates than exhaust valves. The wilder the cam profile, the more pounding the valve and seat undergo at high rpm.
Cooling is more of an issue with exhaust valves because exhaust valves run much hotter than intake valves. Cooling is provided by heat transfer from the valve to seat during the time which the valve is closed, and by conduction up through the valve stem and into the valve guide and head. Titanium valves do not shed heat as quickly as stainless steel valves, so the tradeoff for switching from steel to titanium to save weight is often hotter running valves. The higher the temperature of the exhaust valve, the greater the risk of the valve causing a preignition or detonation problem. There is also increased risk of the valve burning. That's why many suppliers of titanium valves recommend seat materials such as beryllium copper.
Beryllium copper seats are often used in drag racing, NASCAR, Formula 1 and Indy racing because the material works well with titanium valves and has a higher thermal conductivity than steel alloy seats. The main reason why racers use beryllium copper is for cooling the valves.
To find out what kind of seat materials work best in a given application, we asked a number of valve seat suppliers for their recommendations. Here's what they said.
Bob McBroom of Dura-Bond, Carson City, NV, says his company has a variety of seat materials for performance applications. "For racing applications with either stainless steel or titanium valves exhaust valves, we recommend our 30000 Gold Series seat. This is the same seat we sell to Dart and World for their aftermarket performance cylinder heads."
McBroom says the 30000 Gold Series is a sintered valve seat insert, which includes a blend of finely dispersed tungsten carbide in a matrix of tempered M22 tool steel and special alloy iron particles. The powder metal seats have a very uniform microstructure, and are highly machinable. He says that powder metal seats work harden as they age, so they don't have to be as hard initially to provide good long term durability. He also says that the self-lubricating qualities of the material allows it to handle a wide variety of fuels, including unleaded and leaded gasoline, straight alcohol, nitrous oxide and nitro methane. A shot of nitrous will cause combustion temperatures to soar, but the dose usually doesn't last long enough to have any detrimental effect on the seats.
The next step up in Dura-Bond's product line is the 70000 Diamond Series high alloy seat material. "These seats are for applications where high heat resistance is required, such as a propane or natural gas fired stationary engine but also for high performance engines, heavy-duty and extreme duty engines where longevity is a must," says McBroom. The 70000 Diamond Series seats are made out of a high speed tungsten carbide tool steel, which gives it ceramic-like characteristics for extreme temperature resistance.
"We also have low alloy 15000 Series seats that work well with intake valves in performance applications. We have customers who have run our low alloy intake seats in offshore racing boats for hours on end with no harm to the seats."
McBroom says that Dura-Bond has the capacity to custom produce seats for engine builders in small volumes (typically a minimum of 300 pieces). So if an engine builder wants something special, they can be made to order.
"Beryllium copper seats are recommended for racing applications with titanium valves, but we do not sell these kind of seats because they are too expensive and there are too many aftermarket heads and seat sizes," says Rick Emert of SB International, Nashville, TN. "What we have for low end racing are nickel alloy exhaust seats and Cast XB intake seats. For higher end racing, we have nickel seats for pump gas, or cobalt alloy seats for alcohol or nitro fueled engines. We also have stellite seats, but these are for heavy-duty diesel engines. We don't recommend stellite for performance engines because it is too hard and too expensive."
Emert says average combustion temperatures in a street performance engine can range from 1,400° to 1,700° F. He says nickel can handle 1,400° F with no problem, while cobalt is good for up to 1,650° to 1,700° F. With nitrous oxide, temperatures can soar to 4,400° F, which can make some seats become hard and brittle. This increases the risk of seat cracking and failure.
Emert says he doesn't feel powder metal seats are the best choice for performance engines because of the "work hardening" that occurs as they age. "They start out at 25 Rockwell C and can end up at 40 Rockwell C after they age. That's too hard and may cause the seat to shatter."
"We stock iron-based and high nickel alloy seats for stock, street performance and moderate racing applications with our 21-4N stainless steel valves," says Ian Levitt of Qualcast LLC, Nashville, TN. "We make our seats in this country, not China, because some offshore seats are not very consistent metallurgically."
Levitt says Qualcast also has ductile iron seats for use with titanium valves. "Ductile iron seats are the least costly seats for use with stainless steel or titanium valves, but the iron seats must be heat treated properly so they will have a hardness in the mid-30s Rockwell C. You can also use tool steel seats for intake or exhaust valves in medium performance applications, but the hard seats are not compatible with titanium for racing applications."
Levitt says Qualcast also sells a nickel-aluminum-bronze alloy seat for titanium intake valves in racing engines. He says that beryllium copper is best for the exhaust valves in racing engines, but cautioned that beryllium by itself is toxic and must be handled carefully. You should try to avoid breathing any dust that may be given off when cutting or grinding these seats.
"We have a new nickel-silicone-chrome-copper alloy that is a safer alternative to beryllium copper," says Levitt. "It is non-toxic, has better endurance properties and even cools better than beryllium copper. The seats are also made in the USA."
"Many OEM and standard aftermarket aluminum heads come with steel seats already installed, mainly for cost reasons. The steel seats are very compatible with either stainless steel valves or titanium valves. If a customer buys an aftermarket head and wants to put in a set of titanium valves, don't worry because it will be fine," says Bill Wheatley of CV Products, Thomasville, NC.
"On the other hand, if you're using an aluminum head in a racing application or a high heat application such as a turbocharged engine, beryllium copper would be the best seat material. The seats typically contain about 2 percent beryllium, and are called "yellow" seats. Beryllium copper is the material of choice for all types of professional racing. The reason why is because beryllium copper has a tensile strength similar to iron seats, so it won't pound down, and it has the thermal conductivity of the aluminum head. When the valves get hot, the heat radiates right through the valve seat as if the seat was sitting directly on the aluminum head and the valve seat wasn't there at all. It cools that well."
Wheatley says CV Products sells an "A25" alloy for exhaust seats and an "A3" alloy for intake seats. "Both contain 2 percent beryllium and the rest is mostly copper. The only differences are some of the trace elements in the alloy."
Wheatley recommends using beryllium copper for both the intake and exhaust seats, especially in high horsepower engines. "In 600 hp-plus engines for oval track racing, not drag racing, we have seen intake seat erosion where the exhaust seat intersects the intake seat. So much heat is being dumped through the exhaust seat that it affects the intake seat. By the end of the race, the engine is losing compression and will need to have the intake seats replaced. By going to a double yellow arrangement with both seats being beryllium copper, this won't happen. The engine will maintain compression and produce just as much power at the end of the race as when it started the race."
Del West Engineering
Chris Haumont of Del West Engineering, Valencia, CA, says his company sells two different beryllium copper alloys. The "Alloy 25" is for titanium intake valves while the "Alloy 3" is for exhaust valves. Why two different alloys? Haumont says Alloy 3 transfers more heat and provides better cooling for the exhaust valve. But the Alloy 3 is too soft for intake valves so there is a harder Alloy 25 for the intake valves.
"When titanium valves were first introduced years ago, many people were running tool steel or induction hardened seats with a hardness of around 60 Rockwell C. These proved to be too hard for titanium valves, so many racers started using softer ductile or nodular iron seats with a hardness of around 32 Rockwell C.
"Titanium valves are harder to cool than stainless steel valves, so we looked at a variety of materials to see if we could find something that would provide increased cooling, especially for the exhaust valve. Initially, we tried a beryllium copper exhaust seat with nodular iron intake seats. But the slight difference in expansion rates between the beryllium copper and iron seats created a cracking problem in the head. Using beryllium copper for both seats solved the cracking problem, but we also learned that the alloy we were using for the exhaust side didn't work as well on the intake side. As a result, we came up with different beryllium copper alloys for the intake and exhaust seats."
Haumont says his company's beryllium copper Alloy 25 is 97 percent copper with 1.8 to 2.0 percent beryllium, and has a hardness of 38 to 41 Rockwell C. The Alloy 3, by comparison, is 98 percent copper, contains less beryllium (0.2 to 0.6 percent) but adds nickel (1.4 to 2.2 percent), and has a hardness of 95 to 102 Rockwell B (roughly 20 on the Rockwell C scale). By comparison, ductile iron seats typically have a hardness of around 32 Rockwell C.
"Beryllium copper works great in a racing engine with titanium valves, but there is no advantage to using beryllium copper with steel valves because you don't really need the extra cooling. Beryllium copper seats would also require more maintenance in a street engine than ductile iron seats," says Haumont.
According to Joseph Keon of Martin Wells International, Los Angeles, CA, because titanium valves are so expensive, some racers would rather lose their seats than scuff up their valves by using seats that deliver better performance. "The higher the quality of the seat, the more it will wear titanium valves," says Keon. "A set of titanium valves may cost $480. A set of inexpensive cast iron seats may be less than $20. Some of these racers think it's cheaper to replace the seats after a race than to use better seats that may wear their valves."
Keon says his company's "Well-Tite" valve seat alloy forms a film that actually protects the valve and seat. Consequently, valve wear is not a problem in stock or performance applications.
Forty years ago Martin Wells introduced its Well-Tite formula that achieves the same wearability of a 52 Rockwell C stellite type of product but with a hardness of only 35 to 37. And it does a far better job of dissipating heat, says Keon. The Well-Tite alloy contains 42 percent nickel, which sucks the heat away from the valve. It has 10 to 12 percent chrome for oxidation, and 7 percent moly for toughness. The formula produces an iron-chromium oxide layer that develops on the surface of the seat, and acts like a solid lubricant to prolong valve and seat life.
The Well-Tite seats are not heat treated, but are machined and sold "as cast." This allows the seats to handle high temperatures without danger of grain inversion. The material also won't distort, causing the seats to loosen and fall out.
Precision Engine Parts
"It's not easy to make a specific recommendation for what type of seat material to use in a performance engine because engine builders today are using a wide range of materials with good results," says Dale McKitterick of Precision Engine Parts, Las Vegas, NV. "And many prefer to stick with a familiar product."
McKitterick explains that times, and preferences, have changed. "Fifteen years ago, I felt strongly that ductile iron seats were the best choice for performance engines. Longevity was not a big issue then because most of these engines were being torn down after 500 miles. But now people are buying aftermarket aluminum performance heads, putting them on street engines and expecting them to hold up like a stock head. Ductile iron seats work great in aluminum heads because the heads dissipate heat so quickly. But with cast iron performance heads, I think high chrome alloy seats or our M2 tool tungsten steel alloy seats are a good choice. Summit Racing uses the tungsten seats in their heads. The tungsten alloy work hardens and can really take a beating. We recommend it for marine applications, heavy-duty engines, dry fuel engines, and for racing," says McKitterick.
"When most people think high performance racing engines, they're thinking titanium valves," says Phillip Carrasco, Tucker Valves, Odessa, TX. "Titanium valves are probably used in 80 to 85 percent of these applications, and most racers say they want beryllium copper seats. But there is only limited production of beryllium copper in the US, so we do not sell these type of seats. We offer ductile iron seats that we think are more forgiving when used with titanium valves."
Carrasco says beryllium copper is used mostly for heat dissipation purposes, not wear resistance.
"Our premium seat is an iron-based chrome moly with tungsten and vanadium. It was created primarily for natural gas irrigation engines, but it also works great in most automotive applications. It wears well and works great in a street performance engine."
Because seats are press-fit into aluminum heads, the amount of interference fit is critical to ensure proper seat retention and to prevent head or seat cracking. Many engine builders have their own personal preferences for how much interference fit to use, which may or may not agree with what seat suppliers or OEMs recommend.
Some seat suppliers say they recommend .003" to .007" interference fit for seats that are being installed in cast iron cylinder heads, and .005" to as much as .008" of interference fit for seats that are going into aluminum heads depending on the diameter of the seat (the wider the seat, the greater the recommended interference fit). Others say .003" to .005" is all the interference that's needed in an aluminum head provided the counterbores for the seats are machined correctly and have a nice smooth finish. By comparison, the typical OEM recommendation for interference fit in most aluminum heads is only about .003".
For best results, use a lubricant or coolant when cutting seat counterbores in aluminum heads, make sure the cutters are sharp, and don't use the same tool bits on aluminum that have been used on cast iron heads. Also, use plenty of cutting speed: 600 rpm should leave a smooth finish that will require a minimum press fit.
If the replacement seat has a sharp edge, it should be chamfered or rounded so it won't scrape any metal off the head as it is being driven into position (some seats come with a chamfer already on them). If metal gets under the seat, it will create a gap that forms a heat barrier. This, in turn, will interfere with the seat's ability to cool the valve and premature valve failure will likely result.
Preheating the head and/or chilling the seats will also make installation easier and lessen the danger of broaching the counterbore as the seat is being pushed into place.
Virtually all of the seat suppliers say it is not necessary to use an anaerobic locking compound, staking or peening to "lock" the seats in place provided the seats are installed with sufficient interference fit and the seat counterbores have a smooth finish. Several say use of a locking compound may form a "thermal barrier" between the seat and result in heat that could slow heat transfer and cooling. We called a leading supplier of anaerobic locking compounds to ask about this, and were told that locking compounds are "not highly conductive," but should have a negligible effect on seat cooling in this type of application.
Removing beryllium copper seats may be tricky because the material cools so well you can't weld a bead to the seat to shrink it loose. The recommended removal procedure is to bore or cut the seat out.