Teufelhunden
08-04-2006, 05:00 PM
:banana1: :bday :banana1:
Looked high and low for a b-day gift for ya...here you go:goof
A Quick Look At My Engine Ideas
I am an engine enthusiast to say the least. Cubic dollars have prevented me from furthering my involvement in race engines other than my own bracket car and engines in some of my friends’ cars. My ideas come from my studies as a mechanical engineer and reading technical data of any shape or form pertaining to engine theory.
In 1988, I began formulating a simple calculation that would enable me to approximate the power level of a particular engine size and family, based on intake flow and rpm. At that time, I was using maximum cylinder head flow in my calculations and assigning compression ratios to a particular cam duration. Since then, I have quantified the role of port volume/area as well as cylinder pressure in the engine parameters. My engine calculations are continually evolving and are getting fairly detailed, however most of the last few years (since '95) have been spent formulating valve timing calculations. After several years of relying on curve-fit equations for rpm versus duration, I came to the realization that this was not reality. The equations provided a very convenient baseline; but at some point, valve timing must become a collection of opening and closing points, not an imposed duration value.
I am including general ideas on cylinder heads, cams, and to a lesser degree (but no less important) intake manifolds and headers because these components are among the most common bolt-on parts, and therefore the most commonly mismatched parts.
Cylinder Head Requirements:
Intake Flow:
Maximum runner flow is somewhat meaningless without the total flow curve throughout the complete lift range of the cam. Flow occurs from the time the valve is opened and until it is closed. If the flow values do not match the needs of the engine throughout the lift range, then the ability to make good power is gone everywhere but at that those specific matching valve lifts. The end result is poor cylinder filling because of flow inadequacies. If you apply this power loss to every cylinder over the whole rpm range, it becomes quickly apparent that the power output has taken a significant hit. In short, the cylinder is not adequately being filled and the cylinder pressure is suffering. Inadequate cylinder pressure adds up to reduced torque.
A useful relationship to keep in mind is the runner's flow per cross-sectional area. If the flow area is calculated over the entire lift range and divided by port's cross-sectional area, the resulting proportion is a great benchmark for comparing runner effectiveness. Using a method like this helps to average the total flow capability, over the complete valve lift range, and yields a more realistic look at the power output based on intake flow capability.
Exhaust Flow:
This is an area where my theories may deviate from what I classify as normal thinking. Correct flow quality must be maintained within the cam’s lift range, just as on the intake port. I think of the exhaust port as an extension of the valve seat/bowl geometry and the header tube as the actual exhaust runner. Because of this relationship, the header tube should be installed when flow data is taken on the exhaust, or at least a tube stub simulating the header diameter and transition with enough length to introduce flow losses like the actual header. All modifications to the port cross-section should be in the interest of maintaining an effective transition into the header tube, as well as increasing flow. The exhaust runner will behave differently than the intake runner because it is a tube with constant cross-section (usually). Short of using inertial wave effects to improve the overall port effectiveness, optimizing the seat geometry, valve bowl area, and effectively transitioning the flow to the header tube is about all than can be done because the maximum flow capability is dictated by the port's cross-sectional area. The header primary tube is the critical dimension in the exhaust path and therefore controls maximum flow capability. This total flow is even effected by the exhaust system as a whole.
Runner Volume and Cross-Sectional Area:
Runner Volume, like maximum runner flow, is meaningless without the complete picture. The port's cross-sectional area is the real parameter to characterize. Compare the small block Chevrolet intake port volume to the Ford's. A 200cc runner in the Chevrolet head can be considerably different than the same volume in a Ford small block head. The stock Chevrolet runner is about and inch longer, which for a given port volume will yield a smaller port cross section. If runner volume is the only quantity known, then the port length has to be measured to calculate an average cross-sectional area or the port must be disected to find the most representative cross-sectional area. An engine’s torque peak is directly related to the intake and exhaust runner’s cross-sectional area. Large cross-sections, in proportion to the cylinder volume will produce higher rpm torque peaks.
Valve Timing:
Lobe Selection:
The camshaft is the brain of the motor. It controls everything that happens. Because of this, I have basically abandoned all cam catalog applications and go directly to the lobe specification sections. An off-the-shelf cam is a compromise, at best, to get optimum valve timing into a wide range of engine set-ups. Because of this marketing scheme, you see information such as minimum compression ratio, generic intake and exhaust requirements, and rpm ranges for particular families or series of grinds.
Look at two engines, each with the same displacement and geometry, one of which has very large cylinder head runners with very high flow capability and the other with virtually stock heads. Each engine is outfitted with identical intake manifolds and headers/exhaust. The two engines will exhibit very different requirements for valve timing for similar performance and rpm capability. This is the sort of information that is not addressed in most catalog offerings. Equally different, are two engines outfitted identically, but with differing cubic inch displacements. In these examples, assigning camshaft specifications based on broad generalized ideas used by most off-the-shelf marketing techniques can fall short of realistic engine requirements. A camshaft selected on rpm alone is not going to match the engine's performance needs unless the camshaft was designed around a specific set of engine parameters, and your set-up matches it identically.
Cylinder Pressure:
One of my early theories was to apply a minimum static compression ratio to a particular camshaft duration. This was only a part of the puzzle. Compression ratio helps, but what about the low compression motors that make big time horsepower? Cylinder pressure and port velocity are the key players in determining power output. The camshaft is the controlling factor for both of these parameters. By optimizing the timing events within the crank cycle for the required rpm band, the cylinder pressure can be tailored to compliment the engine geometry and components. Typically, the goal is to maximize (or atleast optimize) the cylinder pressure within the engine's intended rpm range.
The media globally labels the Lobe Separation Angle (LSA) as a major selection criteria for choosing a camshaft. Narrower LSA cams are usually touted as having poor idle and driveability characteristics. Part of the reason they have such limited usage guidelines is because of their supposed 'peaky' powerband characteristics. If the cam design is allowed to compliment high port velocity and cylinder pressure for the intended rpm range, then idle and driveability will be no worse than a wider LSA cam used in its correct application, for the same rpm range. In reality, the LSA is a relative value and does not pertain to the intended usage of the engine combination. Poor idle and driveability characteristics come from mismatched components and from the purchase of components with design requirements way out of line from the engine’s needs.
Overlap:
No text on cam design can be complete without discussing overlap. Overlap has been a 'buzzword' around camshaft discussions since hotrodding began. Technically, overlap is the point in the crank cycle at which there is charge exchange during the intake opening and exhaust closing at TDC. It can be an extremely misunderstood process. Like any engine subject: more is better, less is better, it depends on whoever's musings you read or listen to. Which is true, why is there so much contradiction? The media has applied guidelines, like the lobe separation theme, that are unconfounded. The ideas may not be wrong, it's just that the complete story is not told.
Overlap is required to aid in the air exchange, increase the overall breathing capacity of an engine, and tailor rpm band width. Two terms generally associated with overlap are 'scavenging' and 'reversion'. The situation exists that if there is too much pressure in the exhaust, due to flow restriction or inertia wave pulses, then it is possible to reverse the flow in the intake port (reversion). Likewise if the exhaust pressure is too low, creating a vacuum, it is possible for the incoming charge to be sucked past the chamber and go out the exhaust (over-scavenging). The goal is for the pressure differential and charge momentum to be just enough so that the intake charge is helped into the chamber, but the exhaust valve closes just in time to prevent excessive intake charge from being carried out with the exhaust. The key players in determining an engine's overlap requirements are the port cross-sectional areas, flow capability, rod/stroke ratio, static compression, and rpm.
Looked high and low for a b-day gift for ya...here you go:goof
A Quick Look At My Engine Ideas
I am an engine enthusiast to say the least. Cubic dollars have prevented me from furthering my involvement in race engines other than my own bracket car and engines in some of my friends’ cars. My ideas come from my studies as a mechanical engineer and reading technical data of any shape or form pertaining to engine theory.
In 1988, I began formulating a simple calculation that would enable me to approximate the power level of a particular engine size and family, based on intake flow and rpm. At that time, I was using maximum cylinder head flow in my calculations and assigning compression ratios to a particular cam duration. Since then, I have quantified the role of port volume/area as well as cylinder pressure in the engine parameters. My engine calculations are continually evolving and are getting fairly detailed, however most of the last few years (since '95) have been spent formulating valve timing calculations. After several years of relying on curve-fit equations for rpm versus duration, I came to the realization that this was not reality. The equations provided a very convenient baseline; but at some point, valve timing must become a collection of opening and closing points, not an imposed duration value.
I am including general ideas on cylinder heads, cams, and to a lesser degree (but no less important) intake manifolds and headers because these components are among the most common bolt-on parts, and therefore the most commonly mismatched parts.
Cylinder Head Requirements:
Intake Flow:
Maximum runner flow is somewhat meaningless without the total flow curve throughout the complete lift range of the cam. Flow occurs from the time the valve is opened and until it is closed. If the flow values do not match the needs of the engine throughout the lift range, then the ability to make good power is gone everywhere but at that those specific matching valve lifts. The end result is poor cylinder filling because of flow inadequacies. If you apply this power loss to every cylinder over the whole rpm range, it becomes quickly apparent that the power output has taken a significant hit. In short, the cylinder is not adequately being filled and the cylinder pressure is suffering. Inadequate cylinder pressure adds up to reduced torque.
A useful relationship to keep in mind is the runner's flow per cross-sectional area. If the flow area is calculated over the entire lift range and divided by port's cross-sectional area, the resulting proportion is a great benchmark for comparing runner effectiveness. Using a method like this helps to average the total flow capability, over the complete valve lift range, and yields a more realistic look at the power output based on intake flow capability.
Exhaust Flow:
This is an area where my theories may deviate from what I classify as normal thinking. Correct flow quality must be maintained within the cam’s lift range, just as on the intake port. I think of the exhaust port as an extension of the valve seat/bowl geometry and the header tube as the actual exhaust runner. Because of this relationship, the header tube should be installed when flow data is taken on the exhaust, or at least a tube stub simulating the header diameter and transition with enough length to introduce flow losses like the actual header. All modifications to the port cross-section should be in the interest of maintaining an effective transition into the header tube, as well as increasing flow. The exhaust runner will behave differently than the intake runner because it is a tube with constant cross-section (usually). Short of using inertial wave effects to improve the overall port effectiveness, optimizing the seat geometry, valve bowl area, and effectively transitioning the flow to the header tube is about all than can be done because the maximum flow capability is dictated by the port's cross-sectional area. The header primary tube is the critical dimension in the exhaust path and therefore controls maximum flow capability. This total flow is even effected by the exhaust system as a whole.
Runner Volume and Cross-Sectional Area:
Runner Volume, like maximum runner flow, is meaningless without the complete picture. The port's cross-sectional area is the real parameter to characterize. Compare the small block Chevrolet intake port volume to the Ford's. A 200cc runner in the Chevrolet head can be considerably different than the same volume in a Ford small block head. The stock Chevrolet runner is about and inch longer, which for a given port volume will yield a smaller port cross section. If runner volume is the only quantity known, then the port length has to be measured to calculate an average cross-sectional area or the port must be disected to find the most representative cross-sectional area. An engine’s torque peak is directly related to the intake and exhaust runner’s cross-sectional area. Large cross-sections, in proportion to the cylinder volume will produce higher rpm torque peaks.
Valve Timing:
Lobe Selection:
The camshaft is the brain of the motor. It controls everything that happens. Because of this, I have basically abandoned all cam catalog applications and go directly to the lobe specification sections. An off-the-shelf cam is a compromise, at best, to get optimum valve timing into a wide range of engine set-ups. Because of this marketing scheme, you see information such as minimum compression ratio, generic intake and exhaust requirements, and rpm ranges for particular families or series of grinds.
Look at two engines, each with the same displacement and geometry, one of which has very large cylinder head runners with very high flow capability and the other with virtually stock heads. Each engine is outfitted with identical intake manifolds and headers/exhaust. The two engines will exhibit very different requirements for valve timing for similar performance and rpm capability. This is the sort of information that is not addressed in most catalog offerings. Equally different, are two engines outfitted identically, but with differing cubic inch displacements. In these examples, assigning camshaft specifications based on broad generalized ideas used by most off-the-shelf marketing techniques can fall short of realistic engine requirements. A camshaft selected on rpm alone is not going to match the engine's performance needs unless the camshaft was designed around a specific set of engine parameters, and your set-up matches it identically.
Cylinder Pressure:
One of my early theories was to apply a minimum static compression ratio to a particular camshaft duration. This was only a part of the puzzle. Compression ratio helps, but what about the low compression motors that make big time horsepower? Cylinder pressure and port velocity are the key players in determining power output. The camshaft is the controlling factor for both of these parameters. By optimizing the timing events within the crank cycle for the required rpm band, the cylinder pressure can be tailored to compliment the engine geometry and components. Typically, the goal is to maximize (or atleast optimize) the cylinder pressure within the engine's intended rpm range.
The media globally labels the Lobe Separation Angle (LSA) as a major selection criteria for choosing a camshaft. Narrower LSA cams are usually touted as having poor idle and driveability characteristics. Part of the reason they have such limited usage guidelines is because of their supposed 'peaky' powerband characteristics. If the cam design is allowed to compliment high port velocity and cylinder pressure for the intended rpm range, then idle and driveability will be no worse than a wider LSA cam used in its correct application, for the same rpm range. In reality, the LSA is a relative value and does not pertain to the intended usage of the engine combination. Poor idle and driveability characteristics come from mismatched components and from the purchase of components with design requirements way out of line from the engine’s needs.
Overlap:
No text on cam design can be complete without discussing overlap. Overlap has been a 'buzzword' around camshaft discussions since hotrodding began. Technically, overlap is the point in the crank cycle at which there is charge exchange during the intake opening and exhaust closing at TDC. It can be an extremely misunderstood process. Like any engine subject: more is better, less is better, it depends on whoever's musings you read or listen to. Which is true, why is there so much contradiction? The media has applied guidelines, like the lobe separation theme, that are unconfounded. The ideas may not be wrong, it's just that the complete story is not told.
Overlap is required to aid in the air exchange, increase the overall breathing capacity of an engine, and tailor rpm band width. Two terms generally associated with overlap are 'scavenging' and 'reversion'. The situation exists that if there is too much pressure in the exhaust, due to flow restriction or inertia wave pulses, then it is possible to reverse the flow in the intake port (reversion). Likewise if the exhaust pressure is too low, creating a vacuum, it is possible for the incoming charge to be sucked past the chamber and go out the exhaust (over-scavenging). The goal is for the pressure differential and charge momentum to be just enough so that the intake charge is helped into the chamber, but the exhaust valve closes just in time to prevent excessive intake charge from being carried out with the exhaust. The key players in determining an engine's overlap requirements are the port cross-sectional areas, flow capability, rod/stroke ratio, static compression, and rpm.