When choosing valves for your vehicles (car, truck, heavy duty machinary motor cycle), the most misunderstood subject is that of material selection. "DOKURO" offers valves in a variety of materials to meet the requirements virtually any engine.
Some companies only sell one or two materials, and claim that their limited selections are the best for all uses.
An understanding of the environment in which valves must function will prove these claims to be false, as a single material can not meet all operating requirements.
The materials available for "DOKURO" valve applications include carbon steel alloys, stainless steels, inconel, and titanium.

Steel alloys such as SUH|3 or SUH|11 are used in most intake valve and some exhaust valve due to their strength operating tempretures, relatively low cost, and the fat that they can be hardended at the valve tip for durability.

Exhaust valves are made of SUH|35 stainless steel which offers greater high tempreture strength and corrosion resistance.

Since stainless steel alloys are not hardenable, a hardended tip must be welded onto the stem.
Inconel is a nickel alloy rarely used in automotive engines,though it may be required for extremely high tempretures such as those found in turbo charged vehicles.
Titanium is a strong, lightweight, but expensive material used in maximum output racing engines.
The main benefit of titanium is a reduction in valve weight, allowing higher engine speeds.

The key difference between intake and exhaust valves is the tempreture at which they operate. the exhaust valve is regularly subject to highly corrosive exhaust gasses at tempretures that may exceed 1400 degrees fahrennheit or 560 cnetigrate. in comparison, the intake valve are cooled by the inoming fuel and air mixture, and do not reach such high tempretures.
The lower cost steel alloysa may actually be stronger than exhaust valve stainless when they are compared at the lower operating tempreture of an intakevalve.

Valve head shape and size are critical to engine performance. Key areas are head diameter, seat angle, and underhead finish. Valve head diameter has a direct impact on airflow and engIne power. ldeally the valve should be large enough so that it is not a restriction to airflow through the cylinder head. Larger vaIves can be installed in many cylinder heads for improved power potentiaI. IncreasIng the diameter does have a down side, as a significantly larger valve will lessen low end throttle response and torque.
Proper size selection is a compromise between low RPM Peformance and top end power, with the intended use of the engine being the determining factor. lntake valves are normally about 25% greater in diameter than are exhaust valves (in non supercharged engines).


Valve seat angles are usually determined by the engine manufacturer, although they are easily altered by the engine builder.
Unless you have access to a flow bench,it is best to follow the factory recommendations, as the seat angle can have a dramatic impact on performance. Focus your efforts on accuracy when machining the vaIve seat on the cylinder head. Use multiple angles to locate the cyliinder head seat contact area at the proper point on the valve face and maintain minimum seat widths of .045"(1mm) on the intake, and .060"(1.5mm) on the exhaust. A professional job will yield major performance improvements.


The underhead shape and finish of the valve will also influence airflow. Many of our performance valves feature a machined underhead with a precisely formed radius to the valve stem and a finish designed to enhance both flow and valve strength. 0ne area of continued development has been in the replacement of the oIder "swirl poIish" finish with a CNC machining process, this eliminates potential stress risers. Many of our performance valves now employ this techology.


The valve stem must serve as a bearing area for the valve guide, its tip must be durable enough to survive constant rocker arm contact, and it must have a groove for retention of the valve spring locks. Stem diameter is determined by the desired strength and weight characteristics.


Flash chrome or chrome plating improves valve stem durability in situations where lubrication is marginal. This is particularly important on the exhaust side where high temperatures are present. To assist engine builders now using aggressive oil control techniques, we plate virtually all of our performance valves. Stem to guide clearances will differ depending on stem diameter, engine application, guide material, and on the type of stem seal selected. Stems that are too "tight" will cause more damage than will those on the "loose" side of specifications. Clearances of .0015"(0.03mm)-.0025"(0.05mm) on thee intakes, and .002"(0.04mm)-.003"(0.06mm) for exhausts are common.

The most common lock style is the single rectangular groove type, a design which has been proven in competition for decades. Parts for this design are available in a variety of materials and angles to meet any need. Multi-groove type locks have been used in O.E. engines for several years.
These allow the valve to rotate independent of the valve spring and retainer, keeping the seating surfaces clean of debris and promoting valve longevity. While street driven vehicles use multi-groove locks without problems, we recommend the single groove style for performance applications. Recently the single radius type groove has been introduced to. market This is not a new design, as it has been used in Europe for many years. While eliminating the "corners" of a rectangular groove, radius grooves are only needed for very small stem diameter valves that have marginal strength. It is rare for an automotive valve of any type to fail in the keeper groove area.

The tip of the valve stem must be quite hard to withstand constant moving contact with the rocker arm. The stainless steel valves cannot be hardened enough to meet this demand, and thus must use either a welded on "hard tip" or a removable lash cap. The non stainless alloys are much more hardenable and do not require tips or lash caps.
Valves using the multi-groove keeper design must be hardened through the entire keeper groove area, thus requiring welded stems when used with stainless head materials.

Valve weight can be an RPM limiting factor in racing engines, and should be considered when building an engine for high speed use. The intake valve gets the most attention in this area due to its larger size and mass.
Titanium valves, though costly, offer dramatic weight savings, extended RPM capability and enhanced valve spring life.


No valve can withstand piston contact if you experience valve head breakage it is almost guaranteed that the cause was piston to valve interference. We recommend a minimum of .100"(2.05mm) clearance, which may sound like a lot.
While you may know someone that got away with a lot less, we've heard from plenty of racers that didn't - so check it and run on the safe side.You can't win if you don't finish the race.

Each valve material has benefits and detriments. Stainless is the material of choice for exhaust valves, but may not be optimal for intake valve use. Alloy steels offer good characteristics for most street and racing intake valve applications. Titanium intake valves are the choice for maximum performance. Weigh the benefits of each type against your performance needs.