valve seat angles and air flow

grumpyvette

Administrator
Staff member

USE THE CALCULATORS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.wallaceracing.com/chokepoint.php
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.velocity-of-sound.com/velocity_of_sound/calculator1.htm

portccvshp.jpg

vechart.gif

http://garage.grumpysperformance.co...alves-and-polishing-combustion-chambers.2630/


Calculating the valve curtain area
The following equation mathematically defines the available flow area for any given valve diameter and lift value:
Area = valve diameter x 0.98 x 3.14 x valve lift
Where 3.14 = pi (π)
For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:
Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches


vgd4.jpg

THROAT.jpg

porting+valve_area.jpg


a basic but effective valve job with blended port bowl area clean -up helps flow rates
exvls1.png

instv1.png


valve-dr2.jpg

valve-dr1.jpg

Unless rotary valves are perfected, poppet valves will continue to be the crucial moving airflow component in today’s high-performance engines. Their shape, material selection and preparation can make or break an engine’s ultimate performance, regardless of the development of high-profile parts like cylinder heads and induction systems.

“Engine valves exert enormous influence on engine airflow, mixture quality and the ability to run higher engine speeds,” says Zeke Urrutia of Ferrea Racing Components, which manufacturers of high-performance racing valves and valvetrain components.
The valves must provide a perfect seal at all engine speeds, and their size, shape and seat angles must support the best possible mixture movement through the flow window. Specific materials are also required to maintain durability in the harsh combustion environment, but valve weight is also a paramount consideration to ensure effective high speed operation. In essence, there is much more to the ordinary engine valve than fundamentally meets the eye.

While the broad science of engine airflow is surprisingly complex, this report will focus on the basic content and function of engine valves and how they contribute to engine performance. The conventional valve and valve-seat configuration has proved to be the most practical way of feeding an engine. Unfortunately, this partnership is also the single greatest restriction to engine airflow. While port shape, length and cross section are the primary considerations of engine airflow dynamics, the throat area just above the valve is the most restrictive and the most crucial element of optimum airflow and mixture quality. In fact, the area approximately ½-inch above and below the intake valve is the most influential factor of the entire inlet flow path. Maintaining good airspeed past the rapidly opening and closing valves is the engine builder’s top priority.
Enhancing mixture quality

Multi-angle valve jobs are used to ease the flow transition from the port to the chamber on the intake side and from the chamber to the port on the exhaust side. The width, number and concentricity of these cuts influence sealing effectiveness and flow quality.

“A properly configured valve and valve seat angle can significantly improve air flow and enhance mixture quality at the same time,” stresses Urrutia.

Steady-state airflow past an open valve (on a flow bench) is one crucial measure, but starting and stopping that column of air (and fuel droplets) many times per second is not conducive to the smooth transfer of the fuel/air medium from the induction system. And it is certainly not supportive of good mixture quality when fuel droplets are violently slammed against the back of the valve at high speed and just as quickly accelerated and flushed past the seat into the cylinder where a whole different pressure environment exists.

The valve is a simple variable-geometry device that controls the opening and closing of the specified flow window or valve curtain area as determined by the camshaft and rocker ratio. The valve curtain area is defined as the flow window created by the open valve at maximum valve lift. To calculate valve curtain area you can’t go by the valve diameter itself. You have to use the flow diameter, which is where the actual valve seat begins and that is generally about .040-inch smaller than the measured valve diameter. A generally accurate formula for the flow diameter is multiplying the valve diameter by 0.98 (see sidebar).

Calculating the valve curtain area

The following equation mathematically defines the available flow area for any given valve diameter and lift value:

Area = valve diameter x 0.98 x 3.14 x valve lift

Where 3.14 = pi (π)

For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:

Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches

Maximum valve opening, rate of opening and length of time the valve is open are controlled by the camshaft, but the valve size, shape and seat angles have a profound effect on overall airflow efficiency.

If we accept that airspeed and net mass flow are the key components of cylinder filling, it’s easy to see that moving high-velocity air past the valve and into the combustion chamber smoothly with minimal turbulence is critical to optimizing performance. Engine builders refer to this as pressure recovery or the efficient slowing of high velocity air and transforming kinetic flow energy into cylinder pressure. In the runner and past the valve, air velocity is high and the static pressure is low. Inside the cylinder, pressure is higher and airspeed is reduced due to the dramatic change in area. A gradual transition from low static pressure and high velocity past the valve to higher static pressure and low velocity in the cylinder aids cylinder filling and makes the most efficient use of a properly designed port.



Equal airflow

“This depends greatly on the shape of the combustion chamber, but the real key is to get the airflow as equal as possible around the entire circumference of the valve,” explains Urrutia. “This is difficult to achieve because the port almost always approaches the valve from an oblique angle, and flow is kinetically biased to follow its own preferred direction — which rarely favors even flow around the valve.”

Flow dynamics are further complicated when the combustion chamber typically shrouds 30 or more percent of the valve. That’s why pocket porting and unshrouding the valve picks up power, but the valve shape and seat angles play a significant role in optimizing flow efficiency and mixture quality through effective fuel shearing across the seat.

Titanium valves offer multiple benefits, despite their higher initial cost. — Zeke Urrutia, Ferrea

The role of the valve is critical at all lift values, but a key proportion is the LD ratio — or the lift-to-diameter ratio — where the lift value equals one-quarter of the valve’s diameter. Regardless of valve diameter, at this point the valve curtain area is exactly equal to the valve head area.

“Everything below this strongly influences low-lift flow,” says Urrutia, “which is an important function of overcoming fuel-mixture inertia.”



Unless rotary valves are perfected, poppet valves will continue to be the crucial moving airflow component in today’s high-performance engines. Their shape, material selection and preparation can make or break an engine’s ultimate performance, regardless of the development of high-profile parts like cylinder heads and induction systems.

“Engine valves exert enormous influence on engine airflow, mixture quality and the ability to run higher engine speeds,” says Zeke Urrutia of Ferrea Racing Components, which manufacturers of high-performance racing valves and valvetrain components.

An open valve creates a flow window defined by the valve seat flow diameter and the amount of lift created by the camshaft. At most lift values a significant portion of the flow window is partially obstructed by the combustion chamber walls, making it difficult to obtain equal flow around the entire circumference of the valve.

The valves must provide a perfect seal at all engine speeds, and their size, shape and seat angles must support the best possible mixture movement through the flow window. Specific materials are also required to maintain durability in the harsh combustion environment, but valve weight is also a paramount consideration to ensure effective high speed operation. In essence, there is much more to the ordinary engine valve than fundamentally meets the eye.

While the broad science of engine airflow is surprisingly complex, this report will focus on the basic content and function of engine valves and how they contribute to engine performance. The conventional valve and valve-seat configuration has proved to be the most practical way of feeding an engine. Unfortunately, this partnership is also the single greatest restriction to engine airflow. While port shape, length and cross section are the primary considerations of engine airflow dynamics, the throat area just above the valve is the most restrictive and the most crucial element of optimum airflow and mixture quality. In fact, the area approximately ½-inch above and below the intake valve is the most influential factor of the entire inlet flow path. Maintaining good airspeed past the rapidly opening and closing valves is the engine builder’s top priority.



Enhancing mixture quality

Multi-angle valve jobs are used to ease the flow transition from the port to the chamber on the intake side and from the chamber to the port on the exhaust side. The width, number and concentricity of these cuts influence sealing effectiveness and flow quality.

“A properly configured valve and valve seat angle can significantly improve air flow and enhance mixture quality at the same time,” stresses Urrutia.

Steady-state airflow past an open valve (on a flow bench) is one crucial measure, but starting and stopping that column of air (and fuel droplets) many times per second is not conducive to the smooth transfer of the fuel/air medium from the induction system. And it is certainly not supportive of good mixture quality when fuel droplets are violently slammed against the back of the valve at high speed and just as quickly accelerated and flushed past the seat into the cylinder where a whole different pressure environment exists.

The valve is a simple variable-geometry device that controls the opening and closing of the specified flow window or valve curtain area as determined by the camshaft and rocker ratio. The valve curtain area is defined as the flow window created by the open valve at maximum valve lift. To calculate valve curtain area you can’t go by the valve diameter itself. You have to use the flow diameter, which is where the actual valve seat begins and that is generally about .040-inch smaller than the measured valve diameter. A generally accurate formula for the flow diameter is multiplying the valve diameter by 0.98 (see sidebar).

Calculating the valve curtain area

The following equation mathematically defines the available flow area for any given valve diameter and lift value:

Area = valve diameter x 0.98 x 3.14 x valve lift

Where 3.14 = pi (π)

For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:

Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches

Maximum valve opening, rate of opening and length of time the valve is open are controlled by the camshaft, but the valve size, shape and seat angles have a profound effect on overall airflow efficiency.

If we accept that airspeed and net mass flow are the key components of cylinder filling, it’s easy to see that moving high-velocity air past the valve and into the combustion chamber smoothly with minimal turbulence is critical to optimizing performance. Engine builders refer to this as pressure recovery or the efficient slowing of high velocity air and transforming kinetic flow energy into cylinder pressure. In the runner and past the valve, air velocity is high and the static pressure is low. Inside the cylinder, pressure is higher and airspeed is reduced due to the dramatic change in area. A gradual transition from low static pressure and high velocity past the valve to higher static pressure and low velocity in the cylinder aids cylinder filling and makes the most efficient use of a properly designed port.



Equal airflow

“This depends greatly on the shape of the combustion chamber, but the real key is to get the airflow as equal as possible around the entire circumference of the valve,” explains Urrutia. “This is difficult to achieve because the port almost always approaches the valve from an oblique angle, and flow is kinetically biased to follow its own preferred direction — which rarely favors even flow around the valve.”

Valve angle relative to the cylinder bore influences flow characteristics. A raised port and shallower valve angle improves flow by providing a straighter flow path and reduced valve shrouding. In some cases a slightly smaller valve will perform better because it helps to overcome the effects of shrouding.

Flow dynamics are further complicated when the combustion chamber typically shrouds 30 or more percent of the valve. That’s why pocket porting and unshrouding the valve picks up power, but the valve shape and seat angles play a significant role in optimizing flow efficiency and mixture quality through effective fuel shearing across the seat.

Titanium valves offer multiple benefits, despite their higher initial cost. — Zeke Urrutia, Ferrea

The role of the valve is critical at all lift values, but a key proportion is the LD ratio — or the lift-to-diameter ratio — where the lift value equals one-quarter of the valve’s diameter. Regardless of valve diameter, at this point the valve curtain area is exactly equal to the valve head area.

“Everything below this strongly influences low-lift flow,” says Urrutia, “which is an important function of overcoming fuel-mixture inertia.”

The accompanying chart indicates standard valve lengths for popular performance engines. Important dimensions include overall valve length, head diameter, margin height and tip length.

Above this point, the engine builder needs to compare the minimum port cross-sectional area (typically the throat area above the valve) to the valve curtain area. Somewhere around the mid-lift point, the valve curtain area becomes larger than the port area and the port itself becomes the restriction. This is called the saturation lift point. At every point in this equation we are stuck with the same fixed valve shape, seat angles and valve margin dimensions that influence air movement. Above the saturation point, the seat angles are still crucial to maintaining smooth transitional flow and providing a shear edge to help maintain good fuel atomization. The particulars of this are very specific to any given combustion chamber, according to its size, shape, depth, valve position, port texture approaching the valve and, to some degree, the influence of the rising piston crown.

What’s the angle?

A standard 3-angle valve job typically begins with a 60-degree cut in the port throat area to establish a transition to the 45-degree sealing angle that contacts the valve. Above that, a top cut of 15 to 35 degrees typically completes the transition into the combustion chamber. Today many performance valve jobs incorporate up to five different angles, including in some cases a 70- to 75-degree throat cut, depending on the port and its flow characteristics. Generally, inlet flow or exhaust flow does not lose velocity or become turbulent as long as the valve seat or valve angle transitions do not exceed 15 degrees.

The standard seat angle on the valve is 45 degrees. Some applications like Pro Stock drag racing use up to a 55-degree angle on the valve and the seat. This has been found to increase flow, but it is less durable and it cannot be used in supercharged or turbocharged applications because it can’t take the higher temperatures. A 30-degree back cut on the valve helps ease the transition to the seat and a sharp corner on the bottom of the intake valve margin helps resist reversion flow by interrupting its passage back into the port. For most performance applications the intake valve margin height is typically .050-inch and intake valves typically require a tight radius from the stem to the head to prevent low lift restriction.

Exhaust valves generally require the same angles, but use a narrower seat to help the valve cut through carbon buildup and maintain a positive seal. Valve margin should be .080-.090-inch tall to provide durability under higher temperatures and it should have a radius at the bottom to encourage exhaust gas flow around the valve. A tulip shape is often used on exhaust valves to encourage smoother flow.

“This works well, compared to tight radius of intake valves because exhaust gases are still under pressure and can’t wait to get out,” says Urrutia. “Intake mixtures have little relative pressure and must be coaxed into the cylinder through port dynamics.”
valves9.jpg

intake valve (left) has a 30° back cut above the seat and a thin margin with a sharp edge on the bottom to discourage inlet tract reversion. Corresponding exhaust valve has a thicker margin to resist higher temperatures and a generous radius on the bottom to encourage exit flow around the valve. Intake valves use a nail head configuration to avoid flow restriction.
 
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grumpyvette

Administrator
Staff member
One factor I find many guys over look is a bit of logic in selecting components, stop and think things thru, you don,t have to get every factor exactly correct but it helps to get close to matching the components rpm, and air flow rates.
as an example lets take a generic 383 that we will expect to spin and produce good horsepower at 6000rpm.
LSAChart01.jpg

ok at 6000 rpm, combining the info posted a 383 sbc has 47.8 cubic inches per cylinder divided by 2.02=23.7 on the chart above, so youll find cams in the correct duration range having a tight 105-108 lSA most efficient at filling the cylinders in many combos,and you can expect to use a cam with at least 250 degrees duration if your goal is maximizing power at that rpm point, so lets say we select a cam with 255 duration on a 108 LSA..
lets do a bit of math, and keep in mind that a correctly designed header and exhaust system, if matched to the correct cam timing can significantly increase the engines potential power/rpm band
port cross sectional area can be measured and the stall speed , accurately calculated, as can the required matching header configuration, and cam timing, yeah! it takes some reading but the infos readily available

EXFLOWZ4.jpg

just a bit of info on intake gaskets sizes to match port cross sectional areas

portcsa.jpg

Calculating the valve curtain area
The following equation mathematically defines the available flow area for any given valve diameter and lift value:
Area = valve diameter x 0.98 x 3.14 x valve lift
Where 3.14 = pi (π)
For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:
Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches
SO lets do a bit of math
a cylinder head with a 2.02' intake valve and a cam with a .450 lift at the valve with a 1.5:1 rocker will in theory produce a valve curtain area of 2.79 sq inches, swapping to a 1.6:1 ratio increases the lift to .480 lift 2.98 sq inches, increasing the available port flow potential at least in theory by about 6%, but keep in mind the port can only flow at full valve lift for the limited time the valve remains at full lift and if the narrowest section of the port cross sectional areas less that the valve curtain area that not the valve restricts flow




https://www.hotrod.com/articles/1203phr-rethinking-the-valve-job/

https://www.hotrod.com/articles/get-570-hp-small-block-350-chevy-pump-gas/

USE THE CALCULATORS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/
http://www.hotrod.com/articles/choosing-the-right-camshaft/
http://garage.grumpysperformance.com/index.php?threads/bits-of-383-info.38/
porting+valve_area.jpg

if you were to look at a performance big block chevy cylinder head your largest standard intake valve size is either a 2.19" or in a few cases the larger 2.3" valves
a bit of math shows that you won,t reach the max potential flow until valve lift reaches or slightly exceeds about .575-.600 inches of lift with a big block chevy
and a bit more math suggests a minimum of 4.2 square inches of port cross sectional area would be about ideal to match that potential flow,
if you built a 496 BBC stroker that 4.2 SQ inch port would max out at about 6000 rpm and would be best matched with a single plane intake and a cam with a tight 105-106 LSA



CrowerCamTimingChart_108-110.jpg

that timing says the intake valve seat timing at .050 lift is at about 60 degrees so we can assume seat timings close to 75 degrees ABDC
postiongraph.jpg

http://www.kb-silvolite.com/calc.php?action=comp2
a few calculations show a compression ratio close to 10.9:1 -11:1 would be about correct for using pump octane fuel, but ideally youll use race octane gas and a bit higher compression
viewtopic.php?f=52&t=1070
Duration_v_RPM-Range_wIntakeManifold01.jpg


now with 255 degrees intake duration, lifting the valve and we know a 383 cylinder has about 47 cubic inches of displacement , we can calculate that at 6000rpm, we need to fill that 47 cubic inches 3000 times a minute, to maximize the volumetric efficiency, theres 1728 cubic inches in a cubic foot of air, so 47cubic inches times 3000rpm=81.6 cubic foot a minute , but remember the valves on a 720 degree crank shaft rotation cycle and only open for 255 degrees and maybe 75% of that time near its peak flow at best, so a port that flows 300cfm, might sound like its way more than required , but if you realize that 300cfm is constant flow thru the valves curtain area, is reached at about 1/4 of the valve diam. in valve lift. and 75% of 255 degrees, of cam duration leaves only 192 degrees of full flow during that 720 degrees of crank rotation,or about 26% of the time , you have about 75 cfm available to fill the cylinder at least in theory, but other factors like inertia in the intake air column and extra draw from exhaust headers can compensate for some of the loss of flow potential, and remember the piston is not at bottom dead center when the valves close on an engine with a cam having 255 degrees of intake duration,in fact if everything's correctly set up a port that flows about 260 cfm should be more than adequate on a street car engine to maximize the engines power potential
FlatVsRollerChart.gif

volumetric.gif

Fig5LiftCurve_HydSolidRoller800.jpg


http://www.hipermath.com/engines/carburetor_cfm

https://www.enginebuildermag.com/2013/10/cautioning-on-valve-seat-concentricity/





http://garage.grumpysperformance.co...olishing-combustion-chambers.2630/#post-50247

http://garage.grumpysperformance.co...gree-valve-seats-tpi-motors.14662/#post-78724

http://garage.grumpysperformance.com/index.php?threads/how-to-lap-valve-seats.1159/#post-2362

http://garage.grumpysperformance.co...at-angles-and-air-flow.8460/page-2#post-32923

http://garage.grumpysperformance.com/index.php?threads/multi-angle-valve-job-related.3143/
 
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