Dirt track engines are a different breed. Combinations that work for asphalt engines won’t necessarily work in a motor destined for the clay ovals especially engines bound for the midsize to smaller dirt ovals. Circle track engines on typical asphalt tracks have a very narrow powerband that they operate within, and that powerband is generally in the higher RPM range. On the dirt surface, engines must operate in a wider RPM range. Intake and exhaust valve technology is rapidly changing to meet the demands of today’s dirt track powerplants.
Flip through any racing parts catalog and you can quickly be overwhelmed by the vast quantity of engine valves in the marketplace. With terms like: one piece, bi-metallic, stainless steel, undercut, hardened tip…the options in valve choice can be mind numbing. Where does a person start when searching for the best valve options for a dirt track race engine? To get the down and dirty on circle track valve technology, we enlisted the help of Zeke Urrutia of Ferrea Racing Components.
According to Urrutia, Director of Marketing for Ferrea, “It’s all about the material and manufacturing process. For example, certain materials expand on a one piece valve differently than they do on a hollow stem valve. Also, material blends change with time. Take stainless steel for example. Today’s stainless steel is not the same as stainless of ten or fifteen years ago. Now stainless gets added with small amounts of other materials by percentage to make it much stronger than it was fifteen years ago.”
Cylinder Head Technology Changes
Not only do the alloy blends change, but as technology improves, manufacturing techniques and components change with time as well. The standard small block chevy head came stock with 23 degree valve angle on the heads. The valve angle is measured in relationship of the valve to the combustion chamber and deck surface.
Over the years, engine builders and manufacturers looking for more power in the engines, began finding power gains by cutting down the valve angle degrees. It went from the stock 23 degrees to 18-degrees, then 15 or 13-degrees. Higher performance was found at each step. Dart Machinery now offers a cylinder head with the valve angle listed at 9-degrees. “Some valves are particular to some cylinder heads and others are pretty universal depending on the configuration of the cylinder head,” explains Urrutia.
According to Urrutia, “Engine builders continue to experiment with valves that have different material finishes or different valve designs, looking for that extra inch of horsepower.” Which means, what works today may not work as well tomorrow as technical knowledge and quality of materials improve.
When looking for the best set of valves for dirt track racing, with today’s knowledge and materials, it’s most important to understand what you are expecting your motor to do. “The most critical aspect in valve selection for circle track engine builders, or any engine builders for that matter, is choosing the right material for the application,” Urrutia advised.
He continued by saying, “The extreme change of temperature to a valve in the combustion chamber and in the intake manifold area can cause ‘thermal fatigue’. The material’s ability to resist these drastic thermal variations is crucial to the valve life.”
Valve Technology for the Dirt
Urrutia went on to explain dirt track valve selection by race class, “Typically, your weekend circle track racer is restricted by rules and regulated engine components that involve mildly ported or untouched port configuration. These racers will benefit most by paying attention to valve design. Selecting a valve that that flows well is crucial in achieving horsepower in this type of racing.”
“The first consideration is whether you want a one piece or two piece valve,” said Urrutia, adding, “The one piece valve’s tensile strength is higher than a two piece valve. The two piece valve can be as strong as the one piece valve if done properly. Manufactured in a climate controlled environment to reduce contamination in the fuse weld is the key.” It’s not likely that a “white box” two piece valve has been manufactured in that type of controlled environment, so opting for a one piece valve would probably be a more prudent choice for reliability.
Things to look for in a basic street stock valve set is a one-piece valve design constructed out of stainless steel with a hard chrome treatment. Ferrea’s 5000 series valves fits into this profile perfectly. According to Urrutia, “The 5000 series valves undergo a special heat treating process that adds to the exterior hardness of the material. Most of the 5000 series valves are available in an undercut stem and dished head for improved flow characteristics. These type of valves offer the sportsman type racer the maximum value for their dollar.”
For dirt modified and dirt late model racers, a valve with higher fatigue resistance and higher tensile strength is in order. These engines usually have higher valve spring pressures and more aggressive cam profiles which put more stress on the valves. Ferrea’s 6000 series valve fits into this catagory easily. Urrutia explains, “The 6000 series valve is manufactured in a two step slow forging process out of EV8 stainless steel on both the intake and exhaust valves. Then it goes through the same heat treatment process but also undergoes a stress relieving process.”
Stainless steel is often used in exhaust valves because it handles higher heat ranges better than other types of materials. Intake valves are cooled by air passing by them into the combustion chamber where the exhaust valves are continuously exposed to higher temps from the exhaust gasses. In engines where compression is higher and combustion temperatures are higher, stainless steel intake valves are a wise move.
Urrutia explained that highly modified dirt late model engines and sprint car engines, “would benefit from a very high tensile strength valve. These motors tend to rev at a higher RPM, have higher horsepower and demand higher flow. Selecting a valve with aerospace quality alloys, heat treated and stress relieved will offer a higher reliability and resist any metal fatigue due to increased stress loads or higher temperatures.” Ferrea’s Competition Plus line of valves falls into this catagory. According to studies done at Ferrea, the Competition Plus line of valves have a 20 percent increase in tensile strength at high temperature, a 20 percent increase in fatigue resistance and a 25 percent increase in valve seat life.
Zeke gave us some other considerations and options when selecting a valve set for your next engine build:
Bimetallic Forged Valves
Bimetallic Valves are a more advanced design solution for extreme valve train applications that have higher engine heat requirements or the ultimate in tensile strength meaning less valve stem flex. Bimetallic valves are basically manufactured out of two steel rods of different alloy materials that are fused together by welding the two pieces into one component. This method of valve manufacturing is the only approved method for aerospace valve applications. Urrutia explains “The weld point on bimetallic valves is critical. The location of the weld point must remain inside the valve guide area at maximum lift to ensure that it is fully supported at all times.”
Hard Chrome Plating
Hard Chrome Plating on all high performance valves provides the valve stem with a low coefficient of friction and a hard wear-resistant surface. Hard chrome offers the best choice for extreme engine applications by allowing higher lubricity properties and better heat transfer from the valve stem to the valve guide. In short, Hard Chrome Plating on valves lengthens the valves lifespan.
According to Urrutia, “Titanium valves are generally not a good choice for dirt track race engines due to cost and lower life cycle.” While titanium is an ultra lightweight material for valves, the reduced weight comes at a price. “Titanium valves life cycle is limited, especially on the exhaust side. The higher the temperature fluctuation between cool intake air and hot exhaust gasses results in a lower cycle life and frequent replacement of the valve,” Urrutia added.
This type valve is extremely trick and on just about everyone’s Christmas list. Unfortunately, these are cost prohibitive for most Saturday night budget sportsman race teams. However, they are a very sophisticated valve and deserve to be discussed at every level of racing. These valves are manufactured by gun drilling a portion of the valve stem and micro polishing the hollow cavity reducing the weight of the valve by about 20 percent. A special formulated sodium is then added to the hollow valve stem.
According to Urrutia, “The sodium turns from solid to liquid at operating temperature and travels up and down the hollow stem transferring heat from the valve head through the stem to the valve guide. This works extremely well in almost every application. The only caution is with temperatures above 1,650 degrees when the sodium liquid turns into gas and can become dangerous.”
Coatings is another area where technology has advanced significantly in the past few years. We asked Urrutia about the types of coatings that are commonly used on engine valves. The most commonly used coating are Chromium Nitride (CrN) Gold Nitride and Diamond Like Carbon (DLC). When regulations and racing rules mandated a switch to unleaded fuels, race teams found that the reduced amount of protection caused a dry fuel condition that promoted excessive wear to valve faces and seats.
Racing using ethanol and methanol in their fuel systems were already knowledgeable in the erosion and wear issues associated with a dry fuel condition and combated the problem with top end lubrication. Race teams using gasoline as a fuel source opted to experiment with coatings. Urrutia explained the value of these coatings by saying; “Coatings can improve the surface hardness of a component up to 30 to 40-percent. The biggest gains are realized in less face wear, less seat wear because of a harder surface with more lubricity. Thermal coatings can also help by decreasing temperatures by 100 to 200 degrees.”
About Valve Failures
Any valve will wear out eventually, but if your valves quit working long before they should, you need to investigate why. Simply replacing a valve without fixing the underlying problem will result in the same early failure. Let’s take a look at how changes in manufacturing and engine technology have caused early valve failures:
1. Manufacturing Defects. Metallurgical impurities or poor quality materials used in manufacturing valves can leave microscopic cracks, pores or separation in the metal grains. Faulty welds in hollow stem valves that can lead to breakage. Bad chrome plating that flakes off the stem because of poor adhesion.
While you can visually inspect valves for problems, there is no real method of detecting microscopic defect by appearances alone. Your best method of ensuring your valves are free from defects is buying from a reputable supplier or company. While price of less expensive valves from questionable suppliers may be attractive, there is no value if the valve breaks or fails to perform.
Urrutia explained that Ferrea concentrates on using “custom blends of material for racing valves. Ferrea doesn’t get involved in too many ‘off the shelf’ alloys. These materials need to be used in a climate controlled environment to reduce the chance of contamination.” In addition to the materials used, Urrutia told us, “Correct tooling and controlling inconsistencies in manufacturing is important. Manufacturers need to be aware when tools are wearing out and replace them to before the worn tools can cause inconsistent products.”
2. Right Valve for the Job. Burnt valves can be a problem, especially on the exhaust side because of higher temperatures. Exhaust temperatures typically run from 1,200 to 1,350 degrees which make the exhaust valves more prone to erosion and burning that intake valves. Higher operating temperatures require an alloy that can handle the heat. Stainless steel valves or valves with stainless steel heads with a higher chromium and nickel blend are one way to handle higher temps.
Stellite facing and valve seats may also be needed to control erosion and wear. The valves transfer almost 75% of the combustion heat conducted by the valve to the valve seat. If the seat is worn or eroded, the contact patch between the valve and the valve seat is compromised, and so is the heat transfer. The other 25% of conducted heat is dissipated through the valve stem to the valve guides and interstitial space between the valve stem and the valve guide.
Urrutia says, “Sodium filled, hollow stem valves are perfect for higher compression and hotter temp engines. The big secret here is to use high temp material that can withstand a lot of tensile strength. Controlling the stem thickness so that there is perfect concentricity and wall thickness of the hollow stem is extremely important. Keeping the hollow portion of the valve stem within the valve guide at all times is a must. The hollow portion of the valve stem can never be exposed outside the valve guide.”
3. Shock and Awe. Valve breakage happens more often that we’d like, and it can happen on either the intake or exhaust valves with horrible consequences. The two most likely places for valves to break is where the valve head is welded to the stem or at the keeper groove where there is less material.
In either case, parts of the valve will drop into the combustion chamber causing all kinds of damage to the piston, cylinder head and piston wall. The damage caused by a broken valve can leave you in a state of shock and awe.
Thermal shock happens when a sudden temperature change occurs due to shutting off an engine while it is under an extremely high load. This is not as common in circle track racing but can happen with dirt late models and sprint cars that are using two piece valves manufactured with dissimilar metal alloys in the valve head and valve stem.
4. Mechanical encounters of the worst kind. Bent valves, worn valve stems and mushroomed valve stem tips are all symptoms of material rubbing against or striking material. Causes for these maladies range from broken timing chains to cylinder heads that are milled too much and poor lubrication. Regardless of what the cause, simply replacing the valve will not solve the problem if the underlying cause is not corrected.
The large variety of different classes and the wider powerband requirements makes it impossible to define a one size fits all rule for circle track valves. Our experts recommend doing your homework by studying the rules that apply to your division, knowing some specifics about the track that you will be racing on and calling the tech line at Ferrea Racing Components for some special guidance in valve selection. The only rule that applies universally across the board is: choose the valve with the right material blend for your application.