valve tech article
06-21-2004, 06:53 PM
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valve tech article
***** from supertech wrote this article for my site. I think its a good article with lots of good info. There isnt much solid info about valves out there, hope this shines the light on some aspects
Originally Posted by ***** @ supertechperformance.com
This article is designed to open the eyes of a person who is most likely about to get their cylinder head worked on and has the option of upgrading the valves.
Valves are a very important part of the engine, and can lead to a fat headache if you have the wrong valves.
Read up and find out what are the best vavles for your application.
The basics:
A generally good design is:
-One piece valve
-Flows a lot of air
-High Heat Allowances before failure
-Hardened Valve Stem
-Have a set that is designed to work with each other (valve, keeper, & retainer)
-Made in USA, Japan, or Argentina. Most valves (not all) in China are made with the idea of having it cheap as possible to produce, therefore reducing quality of the valve.
-Either back cut, or undercut which results in higher air flow of the valve generally speaking
-CNC Machine Production Process
Bad Design Examples:
-Soft valve stem (tip) resulting in mushroomed valves
-Improper alloy in valves resulting in failure that can be due to different reasons
This article is designed to open the eyes of a person who is most likely about to get their cylinder head worked on and has the option of upgrading the valves. It would be really cool for every consumer to do 20 hours of research and a couple hundred dollars worth of testing on each product they were about to buy but that's not going to happen. So twenty hours of research is a little bit dramatized. It may prove helpful and/or insightful to spend an hour or more and call up head porters, valve manufacturers and shops that sell a lot of valves or have good knowledge of valve technology about their experiences and recommendations.
Advanced
MATERIALS: There are many different grades of materials that have been well classified by the SAE J755 specifications. You have basically 2 groups of carbon alloys: martensitic carbon base alloys with up to 23% of alloy materials and the non-magnetic austenitic alloys with up to 35% percent of alloys. In the first group you will find the materials used in OEM valves. In the second group you will find the Stainless Steel and here the most popular ones are the EV12 (21-2N with 2% of Nickel) or the EV8 (21-4N with 4% of Nickel). Nickel is expensive and is used to increase resistance to high temperature. Then there is another 3rd group of materials that are Nickel based (instead of carbon based materials) being the most popular the Inconel.
Stainless Steel in its different grades, and Inconel, looks pretty much the same and unfortunately there is no way to see the difference other than by doing a laboratory analysis. Inconel (SAE HEV3) though cannot be Nitrided and that is why Inconel valves have to be chromed.
So here, since lab test are expensive, you would have to try to find out to which you trust the most.
Heat Treatments are also very important. It affects the tensile strength of the material and its ductility. It is expensive so some manufacturers just don't do heat treatments or do just one, to lower cost. If you take a valve and bend it more than 90 degrees without breaking it, it's a sign that it has been heat treated to a good level.
Surface finish is also important to avoid areas where a crack can develop and will give you an overall idea of the dedication and importance that the manufacturer gives to the quality of the product.
All materials work fine at low temperatures, but the tensile strength diminishes with the temperature and the Stainless steel and Inconel alloys will hold a higher strength at higher temperatures. Roughly, a Stainless Steel EV8 will allow you to run about 300 F hotter than a OEM material and an Inconel will allow you an additional 200 F of "valve" (exhaust gas temperature is higher) temperature. We have also analyzed the "super alloys" that some manufacturers use on their exhaust valves and we found out that is nothing more that an EV8 stainless steel with the addition of Nb & W, coded XEV-F by SAE. This material is a little stronger than the EV8 up to 1200 F but at 1400 F and higher temperatures the EV8 is stronger according to SAE J775, even though the manufacturer may say that it is even better than Inconel…..
There are also the "one piece forged" valves or the "bimetallic" valves made of two different materials welded at aprox. the middle of the stem. Some welding procedures with compatible materials are very reliable, but there have been many cases of stress concentration and breakage in this area generated by the welding procedure and / or later heat treatment of 2 different materials with different properties. Some Japanese motorcycles today come with Titanium valves that are welded above the head and they are having big problems braking valves. This is going on today with 2 of the most popular Japanese motorcycle manufacturers that are using the same engine.
The tip of the valve has to be hardened. OEM materials can be hardened by heat-treating the tip. Stainless Steel materials cannot be treated in such a way and require the addition of a "hard tip". Usually 2 procedures are used for this purpose: The application of stellite material that is extremely hard but thin, or the addition of a hardened tip, pretty much like a pad of hardened OEM material. The Honda valve train is one of the most aggressive designs in the industry for the valves, considering that they use a rocker arm with a lash adjusting screw with a very small contact area on a small 5.5mm diameter stem. So we found out after some "mushrooming" experiences that the satellite tip does not work well in this application, especially when other very aggressive aftermarket valvetrain components are used (camshafts, springs, valve flotation, etc.).
The stem has to be designed to withstand the stresses of the valve at high rpms and will transmit 25% of the valve heat to the guide. The stem is the area frictioning with the guide so surface finish is important. Chrome may look smooth but under the microscope is a porous material. OEM materials and SS Nitrided valves are smoother on these areas than chromed valves. For high performance applications it is necessary to increase the valve to guide clearance to allow more expansion of the stem due to higher operating temperatures. This may not be necessary in Honda applications that already have a bigger clearance from factory.
The stem is also interfering with the air flow in the port so to reduce this drag the valve is usually necked down (undercut).
An approx. 30 degree back-cut (adjacent to the 45 degree valve seat area) is a common practice in valves for racing applications as it will also allow for increased flow, especially at low valve lifts. An undercut stem can also result in the flow of the valve increasing.
Flat Face vs Dished face valves: Dished face valves are lighter, are more flexible also in the absorption of the impact against the seat at high rmps in the range of 10,000 or higher so they are safer in this sense. Flat face valves are heavier, but increase compression rates (about 0.3-0.6:1 in Honda engines). Most of the times (not always, depends on the engines) flow a little better than dished valves. The flow of flat vs dished will range depending upon what type of combustion chamber work was done and the valve job that was performed on the head. So there is a compromise in the selection of one or the other.
Coating applied: there are mainly two reasons for coating a valve: a) to reduce galling or wear of the stem and/or seat b) to insulate it from heat. OEM materials can be hardened enough by different processes. Stainless Steel material is softer than OEM materials and can be hardened only by Nitriding the surface or by applying a hard chrome coating. Chrome coating is only applied on the stem of the valve because being a coating it could chip away if applied on other areas. Nitriding is a heat treatment that combines with the alloys in the stainless steel producing hard Carbon Nitrites on the surface of the valve. There are other coatings used in valve manufacturing like Molybdenum, Titanium Nitride, DLC, etc, that are quite expensive and for that reason can only be justified in expensive Titanium valves.
Some engine builders have found that insulating the face of the valve with a special coating will reduce the valve temperature. Also keep in mind that less friction between the valve and valve guide will result in less heat and theoretically more power.
OEM vs Aftermarket: OEM valves are good for normally aspirated engines in street cars. They are manufactured with cost in mind. As explained above, hi performance valves are made at higher cost, with more machining involved in order to obtain higher flow rates and with materials more resistant to high temperatures. For N/A engines for "street" performance applications you will get away very well with an OEM valve. For Drag racing or Road racing it is not recommendable to use OEM valves. Now, there are many "aftermarket" products.
Longevity and durability: It is based in the right selection of materials and design for each application and how the complete head has been machined and assembled, as well as the design and characteristics of the complete valvetrain. All should work in harmony but this is very rarely seen in aftermarket products and the first to suffer and blame usually is the valve.
For example, we have seen many aftermarket camshafts with bad or defective ramp designs that are very aggressive on the valve tips.
A machined seat insert that is not concentric with the guide will force the valve to bend in every cycle until it drops a valve head due to fatigue. An improperly machined width on the seat for the exhaust valve may burn an exhaust valve.
OEM materials are hard and have good durability. Nitrided Stainless Steel have a very hard surface and is a very good combination for durability and high temperature applications. Stainless Steel alone is not as hard as OEM materials so as explained above, may ware the guides and the seats will not last as long.
What do engine builders need to know about race valves that they may not know.
Valves and very especially the exhaust valves are being increasingly submitted to higher demands with the increase of engine RPMs, lifts, turbo boost, Nitros, etc. Under these conditions a valve that is running at over 10,000rpm is opening and closing at a rate of about 80-90 cycles/sec.!!!!!. Think for a moment….at 80 times per second it has very little time to transfer its heat to the cylinder head (which is approximately done 75% through the seat and 25% through the guide.
So it is very important to give increasing consideration to the surface finishing and largest possible seat width to match the valve when machining the valve seats to increase the cooling capabilities of the valves and avoid valve failures problems.
Failure problems could be burning or breakage because when an Exhaust valve cannot dissipate the heat properly, it will increase the temperature in each cycle reaching levels far beyond the materials capabilities, no mater which aerospace, ultra-galactic or how sophisticated is the material alloy used, it will reach its limit at some point and will fail without any indication for the non-trained eye.
What is some final information about race valves? Respect them a lot !!. Their job is unbelievable difficult in today's racing engines. Pay attention to seat-guide concentricity, perpendicularity, surface finish, oil flow, oil and water temperatures, spark timing, advance and so on….every detail could make their job easier or unbelievable worse… If you ask your head porter or local machine shop about the above factors and they say thats its not important, then go find someone else to do work on your head.
Valves are a very important part of the engine, and can lead to a fat headache if you have the wrong valves.
Read up and find out what are the best vavles for your application.
The basics:
A generally good design is:
-One piece valve
-Flows a lot of air
-High Heat Allowances before failure
-Hardened Valve Stem
-Have a set that is designed to work with each other (valve, keeper, & retainer)
-Made in USA, Japan, or Argentina. Most valves (not all) in China are made with the idea of having it cheap as possible to produce, therefore reducing quality of the valve.
-Either back cut, or undercut which results in higher air flow of the valve generally speaking
-CNC Machine Production Process
Bad Design Examples:
-Soft valve stem (tip) resulting in mushroomed valves
-Improper alloy in valves resulting in failure that can be due to different reasons
This article is designed to open the eyes of a person who is most likely about to get their cylinder head worked on and has the option of upgrading the valves. It would be really cool for every consumer to do 20 hours of research and a couple hundred dollars worth of testing on each product they were about to buy but that's not going to happen. So twenty hours of research is a little bit dramatized. It may prove helpful and/or insightful to spend an hour or more and call up head porters, valve manufacturers and shops that sell a lot of valves or have good knowledge of valve technology about their experiences and recommendations.
Advanced
MATERIALS: There are many different grades of materials that have been well classified by the SAE J755 specifications. You have basically 2 groups of carbon alloys: martensitic carbon base alloys with up to 23% of alloy materials and the non-magnetic austenitic alloys with up to 35% percent of alloys. In the first group you will find the materials used in OEM valves. In the second group you will find the Stainless Steel and here the most popular ones are the EV12 (21-2N with 2% of Nickel) or the EV8 (21-4N with 4% of Nickel). Nickel is expensive and is used to increase resistance to high temperature. Then there is another 3rd group of materials that are Nickel based (instead of carbon based materials) being the most popular the Inconel.
Stainless Steel in its different grades, and Inconel, looks pretty much the same and unfortunately there is no way to see the difference other than by doing a laboratory analysis. Inconel (SAE HEV3) though cannot be Nitrided and that is why Inconel valves have to be chromed.
So here, since lab test are expensive, you would have to try to find out to which you trust the most.
Heat Treatments are also very important. It affects the tensile strength of the material and its ductility. It is expensive so some manufacturers just don't do heat treatments or do just one, to lower cost. If you take a valve and bend it more than 90 degrees without breaking it, it's a sign that it has been heat treated to a good level.
Surface finish is also important to avoid areas where a crack can develop and will give you an overall idea of the dedication and importance that the manufacturer gives to the quality of the product.
All materials work fine at low temperatures, but the tensile strength diminishes with the temperature and the Stainless steel and Inconel alloys will hold a higher strength at higher temperatures. Roughly, a Stainless Steel EV8 will allow you to run about 300 F hotter than a OEM material and an Inconel will allow you an additional 200 F of "valve" (exhaust gas temperature is higher) temperature. We have also analyzed the "super alloys" that some manufacturers use on their exhaust valves and we found out that is nothing more that an EV8 stainless steel with the addition of Nb & W, coded XEV-F by SAE. This material is a little stronger than the EV8 up to 1200 F but at 1400 F and higher temperatures the EV8 is stronger according to SAE J775, even though the manufacturer may say that it is even better than Inconel…..
There are also the "one piece forged" valves or the "bimetallic" valves made of two different materials welded at aprox. the middle of the stem. Some welding procedures with compatible materials are very reliable, but there have been many cases of stress concentration and breakage in this area generated by the welding procedure and / or later heat treatment of 2 different materials with different properties. Some Japanese motorcycles today come with Titanium valves that are welded above the head and they are having big problems braking valves. This is going on today with 2 of the most popular Japanese motorcycle manufacturers that are using the same engine.
The tip of the valve has to be hardened. OEM materials can be hardened by heat-treating the tip. Stainless Steel materials cannot be treated in such a way and require the addition of a "hard tip". Usually 2 procedures are used for this purpose: The application of stellite material that is extremely hard but thin, or the addition of a hardened tip, pretty much like a pad of hardened OEM material. The Honda valve train is one of the most aggressive designs in the industry for the valves, considering that they use a rocker arm with a lash adjusting screw with a very small contact area on a small 5.5mm diameter stem. So we found out after some "mushrooming" experiences that the satellite tip does not work well in this application, especially when other very aggressive aftermarket valvetrain components are used (camshafts, springs, valve flotation, etc.).
The stem has to be designed to withstand the stresses of the valve at high rpms and will transmit 25% of the valve heat to the guide. The stem is the area frictioning with the guide so surface finish is important. Chrome may look smooth but under the microscope is a porous material. OEM materials and SS Nitrided valves are smoother on these areas than chromed valves. For high performance applications it is necessary to increase the valve to guide clearance to allow more expansion of the stem due to higher operating temperatures. This may not be necessary in Honda applications that already have a bigger clearance from factory.
The stem is also interfering with the air flow in the port so to reduce this drag the valve is usually necked down (undercut).
An approx. 30 degree back-cut (adjacent to the 45 degree valve seat area) is a common practice in valves for racing applications as it will also allow for increased flow, especially at low valve lifts. An undercut stem can also result in the flow of the valve increasing.
Flat Face vs Dished face valves: Dished face valves are lighter, are more flexible also in the absorption of the impact against the seat at high rmps in the range of 10,000 or higher so they are safer in this sense. Flat face valves are heavier, but increase compression rates (about 0.3-0.6:1 in Honda engines). Most of the times (not always, depends on the engines) flow a little better than dished valves. The flow of flat vs dished will range depending upon what type of combustion chamber work was done and the valve job that was performed on the head. So there is a compromise in the selection of one or the other.
Coating applied: there are mainly two reasons for coating a valve: a) to reduce galling or wear of the stem and/or seat b) to insulate it from heat. OEM materials can be hardened enough by different processes. Stainless Steel material is softer than OEM materials and can be hardened only by Nitriding the surface or by applying a hard chrome coating. Chrome coating is only applied on the stem of the valve because being a coating it could chip away if applied on other areas. Nitriding is a heat treatment that combines with the alloys in the stainless steel producing hard Carbon Nitrites on the surface of the valve. There are other coatings used in valve manufacturing like Molybdenum, Titanium Nitride, DLC, etc, that are quite expensive and for that reason can only be justified in expensive Titanium valves.
Some engine builders have found that insulating the face of the valve with a special coating will reduce the valve temperature. Also keep in mind that less friction between the valve and valve guide will result in less heat and theoretically more power.
OEM vs Aftermarket: OEM valves are good for normally aspirated engines in street cars. They are manufactured with cost in mind. As explained above, hi performance valves are made at higher cost, with more machining involved in order to obtain higher flow rates and with materials more resistant to high temperatures. For N/A engines for "street" performance applications you will get away very well with an OEM valve. For Drag racing or Road racing it is not recommendable to use OEM valves. Now, there are many "aftermarket" products.
Longevity and durability: It is based in the right selection of materials and design for each application and how the complete head has been machined and assembled, as well as the design and characteristics of the complete valvetrain. All should work in harmony but this is very rarely seen in aftermarket products and the first to suffer and blame usually is the valve.
For example, we have seen many aftermarket camshafts with bad or defective ramp designs that are very aggressive on the valve tips.
A machined seat insert that is not concentric with the guide will force the valve to bend in every cycle until it drops a valve head due to fatigue. An improperly machined width on the seat for the exhaust valve may burn an exhaust valve.
OEM materials are hard and have good durability. Nitrided Stainless Steel have a very hard surface and is a very good combination for durability and high temperature applications. Stainless Steel alone is not as hard as OEM materials so as explained above, may ware the guides and the seats will not last as long.
What do engine builders need to know about race valves that they may not know.
Valves and very especially the exhaust valves are being increasingly submitted to higher demands with the increase of engine RPMs, lifts, turbo boost, Nitros, etc. Under these conditions a valve that is running at over 10,000rpm is opening and closing at a rate of about 80-90 cycles/sec.!!!!!. Think for a moment….at 80 times per second it has very little time to transfer its heat to the cylinder head (which is approximately done 75% through the seat and 25% through the guide.
So it is very important to give increasing consideration to the surface finishing and largest possible seat width to match the valve when machining the valve seats to increase the cooling capabilities of the valves and avoid valve failures problems.
Failure problems could be burning or breakage because when an Exhaust valve cannot dissipate the heat properly, it will increase the temperature in each cycle reaching levels far beyond the materials capabilities, no mater which aerospace, ultra-galactic or how sophisticated is the material alloy used, it will reach its limit at some point and will fail without any indication for the non-trained eye.
What is some final information about race valves? Respect them a lot !!. Their job is unbelievable difficult in today's racing engines. Pay attention to seat-guide concentricity, perpendicularity, surface finish, oil flow, oil and water temperatures, spark timing, advance and so on….every detail could make their job easier or unbelievable worse… If you ask your head porter or local machine shop about the above factors and they say thats its not important, then go find someone else to do work on your head.
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