Abstract:
Intake and exhaust valve seat inserts for aircraft cylinder heads. The inserts are configured for low pressure loss as inlet air and hot exhaust gas passes through the respective valve seat inserts. In an embodiment, the intake and exhaust valve seat inserts may have a plurality of faces or facets, at prescribed angles, in order to minimize pressure loss of gases passing therethrough. In an embodiment, rather than a plurality of faces or facets, the intake valve seat sidewall, and/or the exhaust valve seat sidewall may be a provided in the configuration of a smooth curve approximating a set of selected angles, as if the component were made with a plurality of facets.

Description:
RELATED PATENT APPLICATIONS 
       [0001]    This application is a Continuation-In-Part of pending U.S. patent application Ser. No. 13/756,891, filed on Feb. 1, 2013, which application claimed priority from prior U.S. Provisional Patent Application Ser. No. 61/595,049, filed Feb. 4, 2012, entitled CYLINDER HEADS FOR AIRCRAFT ENGINES, the disclosures of each are incorporated herein in their entirety, including their specification, drawing, and claims, by this reference. 
     
    
     COPYRIGHT NOTICE 
       [0002]    A portion of the disclosure of this patent document contains drawing materials that are subject to copyright protection. The owner has no objection to the facsimile reproduction by anyone of the patent document or patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
       TECHNICAL FIELD 
       [0003]    The present disclosure relates to aircraft engines, and more specifically, to improved designs for valve seats in cylinder heads in aircraft engines. 
       BACKGROUND 
       [0004]    Aircraft engines commonly in use in general aviation aircraft are primarily provided in an internal combustion, multi-cylinder, spark ignition configuration which is set up for the combustion of high octane aviation gasoline. Such engines are generally air cooled, with individually mounted cylinders, which in the trade are often called cylinder “jugs”. Cylinder jugs typically include a head portion and a cylinder portion. Each of such portions usually includes a plurality of cooling flanges to exchange heat with air passing the cylinder. Each engine is configured to route incoming combustion air through the head portion to the cylinder, and to route the hot exhaust gases out of the cylinder through the head portion to an exhaust header or manifold. Control of relatively cool combustion air entering the cylinder, and of hot exhaust gases leaving the cylinder, is accomplished by intake and exhaust valves operating in conventional fashion. 
         [0005]    Cylinder heads in current general aviation aircraft engine designs include inlet passageways for incoming air flow, and outlet passageways for the outgoing exhaust gases, each of which passageways were in most cases designed decades ago. Little attention seems to have been given to optimizing the engine power output by optimization of the flow path for the incoming air, or of the flow path for the outgoing hot exhaust gases, or to the various portions of the intake valve seat, or to the various portions of the exhaust valve seat. 
         [0006]    In various non-aviation engines, some attempts have been made, with varying degrees of success, to provide an upgrade to the inlet passageways or inlet valve seats, or to the exhaust valve seats or exhaust outlet passageways, to at least in part compensate for poor original designs of cylinder head components. With regard to inlet air passageways, an attempt at obtaining improved performance is described in U.S. Pat. No. 4,159,011, issued Jun. 26, 1979, for an Engine Cylinder Inlet Port, and which was assigned to General Motors Corporation, of Detroit, Michigan. In the described apparatus, a shaped flow deflector provided some improvement with respect to inlet air flow; however, that design leaves considerable room for improvement. With regard to exhaust gas outlet passageways, an attempt to obtain improved performance is described in U.S. Pat. No. 4,537,028, issued Aug. 27, 1985, for an Exhaust Port, and which is assigned to Deere &amp; Company, of Moline, Ill.. In that design, flow dividers were provided around a valve stem, which reduced flow separation and loses. However, the configurations of such cylinder heads allow somewhat more latitude in what may be adjusted than the typical aircraft engine cylinder, and the aircraft cylinder heads and passageways therein. 
         [0007]    Thus, in spite of prior art for attempts at improving air flow in other types of internal combustion, multi-cylinder spark ignition engines, there still remains an as yet unmet need for an improved cylinder head, including the intake valve seats and the exhaust valve sates in aircraft engines which can simply and effectively improve total engine power output. It would be advantageous to provide such a design by unique modifications to the current designs used for intake and exhaust valve seats in aircraft cylinder heads, so that adjacent (or other) engine components could be used with little or no modification (except as may be advantageous or necessary to accommodate the air flow volume and power output improvements as taught herein). Importantly, the use of such an improved intake valve seats and exhaust valve seats in an improved cylinder head design would provide increased horsepower output from existing aircraft engines. Such improvement would be particularly helpful when maximum engine performance is required, such as for short field takeoffs, and/or in high density altitude conditions. Alternatively, and just as important, an improved engine, using improved cylinder head designs as described herein, may be utilized in a method of operation to reduce fuel consumption at a given horsepower output, as compared to fuel consumption rates in engines that use existing cylinder head designs and components. Thus, fuel consumption for a given trip distance would decrease, as compared to a prior art engine design; such improved performance would also extend the range of an aircraft employing such improved cylinder head designs. 
       OBJECTS, ADVANTAGES, AND NOVEL FEATURES 
       [0008]    Novel cylinder heads for aircraft engines as disclosed herein include an inlet passageway that is optimized to allow maximum airflow, by minimizing pressure drop (friction and flow turbulence losses) of air traversing through the inlet air passageway. Further, the inlet valve seat is optimized in shape to minimize pressure drop at inlet air flow rates. Likewise, the outlet valve seat is optimized in shape to minimize pressure drop as hot exhaust gases pass outward therethrough. And finally, the hot exhaust passageway is optimized to allow maximum exhaust flow, by minimizing the pressure drop (including friction and flow turbulence losses) experienced by exhaust gases, by minimizing obstructions to the outbound passage of high velocity hot exhaust gases. 
         [0009]    The novel cylinder heads described herein are particularly advantageous in that they are configured to allow installation by an engine manufacturer on a new engine otherwise using existing design configurations, and thus allowing an increase in the horsepower output without the necessity to modify various other existing components. And, such novel cylinder heads (including novel intake and exhaust valve seats) could be substituted in the field, for example, during a “top overhaul” of an aircraft engine, to likewise improve horsepower output of a selected engine, and/or to reduced fuel consumption at a selected power output, as compared to the stock cylinders and heads. Such novel cylinder heads may be provided for overhauls as the key component of factory provided new cylinder kits for use in overhauls of existing engines. 
         [0010]    Further, in an embodiment, it is an advantage that improved intake valves and intake valve seat configurations, and/or improved exhaust valves and exhaust valve seat configurations, may be used to provide yet further increases in power output, and in fuel economy, as compared to cylinder designs that only include new, improved inlet passageway and/or exhaust passageway designs described herein. 
         [0011]    It is an advantage that improved cylinder heads provided by the designs disclosed herein may be manufactured using aluminum alloy castings, as presently used in many existing aircraft cylinder head designs. 
         [0012]    These and other objects, advantages, and novel features of the cylinder head designs for aircraft engines as described herein will become apparent to the reader from the foregoing and from the appended claims, and the ensuing detailed description, as the discussion below proceeds in connection with examination of the accompanying figures of the drawing. 
       SUMMARY 
       [0013]    I have now developed improved intake valve seats and exhaust valve seats designed for aircraft engines. Such components may be easily and quickly installed in existing cylinder heads, or new engines that are otherwise of existing design, or may be easily and quickly installed on used engines, such as during an overhaul, when it may be useful to install new cylinders and related components, such as valves and/or cylinder heads. 
         [0014]    The novel aircraft intake valve seat and exhaust valve seat designs disclosed herein may be scaled up or down as appropriate for the inlet airflow volume and exhaust gas flow volume resulting from the displacement provided by a particular cylinder. As an example, Lycoming Engines (a division of AVCO Corp., a Textron subsidiary), of Williamsport, Pa., produces a line of horizontally opposed, air cooled aircraft engines, with four, six, and eight cylinders, which in various configurations have from about 58 cubic inches displacement per cylinder to about 90 cubic inches displacement per cylinder. While the cylinder bore and head component dimensions for the various displacement sized cylinders are adjusted accordingly, the general principles described and claimed herein may be applied, and size variances easily accommodated. 
         [0015]    The foregoing briefly describes certain aspects and elements of exemplary intake valve seats and exhaust valve seats for use in cylinder heads for aircraft engines, and various components thereof. The various objectives, features and advantages of the invention(s) will be more readily understood upon consideration of the detailed description, taken in conjunction with careful examination of the accompanying figures of the drawing. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]    In order to enable the reader to attain a more complete appreciation of the invention, and of the novel features and advantages thereof, attention is directed to the following detailed description when considered in connection with the accompanying figures of the drawing, wherein: 
           [0017]      FIG. 1  is a partial cross-section view through an embodiment of an aircraft cylinder head, showing the upper reaches of an air cooled cylinder, and showing the cylinder head including a portion of a combustion air inlet passageway in which gas flow has been enhanced by shaping the passageway, an intake valve and associated intake valve guide, the intake valve seat, the upper reaches of the combustion chamber within the cylinder jug, the exhaust valve seat, the exhaust valve with associated exhaust valve guide, and showing a portion of the hot exhaust exit outlet passageway in which gas flow has been enhanced by shaped passageways. 
           [0018]      FIG. 2  provides a side perspective view of an embodiment of an aircraft cylinder head of the type just set forth in  FIG. 1  above, now showing the intake flange and the exhaust flange, and indicating the reduced flow cross-sectional area (at the intake flange) of the combustion air inlet passageway, and of the exhaust gas outlet passageway (at the exhaust flange), as compared to the respective prior art passageway shapes as set forth in broken lines. 
           [0019]      FIG. 3  provides perspective view of a prior art intake valve design for use in an aircraft engine cylinder head. 
           [0020]      FIG. 4  provides a side elevation view of an intake valve design for use in an aircraft engine cylinder head, showing improved intake valve design which enhances flow through the combustion air inlet passageway, as adjacent the intake valve. 
           [0021]      FIG. 4A  provides a partial side elevation view of a portion of an intake valve design for use in an aircraft engine cylinder head, showing details for an improved intake valve design which enhances flow through the combustion air inlet passageway, as adjacent the intake valve. 
           [0022]      FIG. 5  provides perspective view of a prior art exhaust valve design for use in an aircraft engine cylinder head. 
           [0023]      FIG. 6  provides a side elevation view of an exhaust valve design for use in an aircraft engine cylinder head, showing improved exhaust valve design which enhances flow through the hot exhaust gas outlet passageway, as adjacent the exhaust valve. 
           [0024]      FIG. 6A  provides a partial side elevation view of a portion of an exhaust valve design for use in an aircraft engine cylinder head, showing details for an improved exhaust valve design which enhances flow through the hot exhaust gas outlet passageway, as adjacent the exhaust valve. 
           [0025]      FIG. 7  shows a partial cross-sectional view of an aircraft engine cylinder jug, taken transversely through the head portion such as through line  7 - 7  of  FIG. 2 , showing a portion of the cylinder and cylinder head, and the combustion air inlet passageway, with various cross-sections noted, as depicted in  FIG. 8 ,  FIG. 9 ,  FIG. 10 ,  FIG. 11 , and the location of an upward view of the intake valve seat area and upstream combustion air inlet passageway as shown in  FIG. 12 . 
           [0026]      FIG. 8  shows a cross-sectional view taken at line  8 - 8  of  FIG. 7 , indicating the cross-sectional shape at the noted location of an improved combustion air inlet passageway. 
           [0027]      FIG. 9  shows a cross-sectional view taken at line  9 - 9  of  FIG. 7 , indicating the cross-sectional shape at the noted location of an improved combustion air inlet passageway. 
           [0028]      FIG. 10  shows a cross-sectional view taken at line  10 - 10  of  FIG. 7 , indicating the cross-sectional shape at the noted location of an improved combustion air inlet passageway. 
           [0029]      FIG. 11  shows a cross-sectional view taken at line  11 - 11  of  FIG. 7 , indicating the cross-sectional shape at the noted location of an improved combustion air inlet passageway. 
           [0030]      FIG. 12  shows a perspective view, taken at  12 - 12  of  FIG. 7 , indicating the view at the noted location of the outlet of an improved combustion air inlet passageway, as well as the shape of the visible upstream portions of the air inlet passageway. 
           [0031]      FIG. 13  shows a partial cross-sectional view of an aircraft engine cylinder jug, taken transversely through the head portion such as through line  13 - 13  of  FIG. 2 , showing a portion of the cylinder and cylinder head, and the hot exhaust gas outlet passageway, with various cross-sections noted, as depicted in  FIG. 15 ,  FIG. 16 ,  FIG. 17  and  FIG.18 , and the location of an upward view of the exhaust valve seat area and downstream combustion gas outlet passageway as shown in  FIG. 14 . 
           [0032]      FIG. 14  shows a perspective view, taken at  14 - 14  of  FIG. 13 , indicating the view at the noted location and direction of the outlet of an improved hot exhaust gas outlet passageway, and also indicating the shape of the visible downstream portions of the hot exhaust gas outlet passageway. 
           [0033]      FIG. 15  shows a cross-sectional view taken at line  15 - 15  of  FIG. 13 , indicating the cross-sectional shape at the noted location of an improved hot exhaust gas outlet passageway in an aircraft engine cylinder head. 
           [0034]      FIG. 16  shows a cross-sectional view taken at line  16 - 16  of  FIG. 13 , indicating the cross-sectional shape at the noted location of an improved hot exhaust gas outlet passageway in an aircraft engine cylinder head. 
           [0035]      FIG. 17  shows a cross-sectional view taken at line  17 - 17  of  FIG. 13 , indicating the cross-sectional shape at the noted location of an improved hot exhaust gas outlet passageway in an aircraft engine cylinder head. 
           [0036]      FIG. 18  shows a cross-sectional view taken at line  18 - 18  of  FIG. 13 , indicating the cross-sectional shape at the noted location of an improved hot exhaust gas outlet passageway in an aircraft engine cylinder head. 
           [0037]      FIG. 19  provides a side perspective view of an embodiment of an aircraft cylinder head of the type just set forth in  FIGS. 1 and 2  above, now showing the intake flange in detail, and indicating the reduced flow cross-sectional area (at the intake flange) of the combustion air inlet passageway, as compared to the prior art passageway shape as set forth in broken lines, as well as showing typical cooling flanges on the adjacent portions of the cylinder head. 
           [0038]      FIG. 20  provides a side perspective view of an embodiment of an aircraft cylinder head of the type just set forth in  FIGS. 1 and 2  above, now showing the exhaust flange in detail, and indicating the reduced flow cross-sectional area (at the exhaust flange) of the hot exhaust gas outlet passageway, as compared to the prior art passageway shape as set forth in broken lines. 
           [0039]      FIG. 21  is a partial cross-section view through an embodiment of an aircraft cylinder head, similar to that first shown in  FIG. 1  above, but now showing an angled valve design, and wherein the cylinder head is provided in a more hemispherical shape, and showing the cylinder head including a portion of a combustion air inlet passageway in which gas flow has been enhanced by shaping the passageway, an intake valve and associated intake valve guide, the intake valve seat, the upper reaches of the combustion chamber within the cylinder jug, the exhaust valve seat, the exhaust valve with associated exhaust valve guide, and showing a portion of the hot exhaust exit outlet passageway in which gas flow has been enhanced by shaped passageways. 
           [0040]      FIG. 22  is a conceptual view through an embodiment of an aircraft cylinder and head assembly, showing the relationship of the cylinder bore diameter, and the stroke of a piston operating in the cylinder, which together determine the swept displacement volume for the cylinder. 
           [0041]      FIG. 23  is a partial cross-sectional view of an aircraft engine cylinder jug, taken transversely through the head portion such as through line  7 - 7  of  FIG. 2 , showing a portion of the cylinder and cylinder head, and the combustion air inlet passageway, including cross-sectional views of the intake valve seat and associated passageways, and the location of the intake valve seat area as further depicted in  FIG. 24  below. 
           [0042]      FIG. 24  is a partial cross-sectional view of an intake valve seat for an aircraft engine cylinder jug, taken transversely as if located in a cylinder head, showing the angles and relationships of various portions of the intake valve seat which are shaped to provide a smoothly dimensioned intake valve seat to minimize losses, and thus enhance engine performance. 
           [0043]      FIG. 25  shows a partial cross-sectional view of an aircraft engine cylinder jug, taken transversely through the head portion such as through line  13 - 13  of  FIG. 2 , showing a portion of the cylinder and cylinder head, and the hot exhaust gas outlet passageway, with various cross-sections noted above, and further showing the location of a novel exhaust valve seat area as further depicted in  FIG. 26  below. 
           [0044]      FIG. 26  is a partial cross-sectional view of an exhaust valve seat for an aircraft engine cylinder jug, taken transversely as if located in a cylinder head, showing the angles and relationships of various portions of the exhaust valve seat which are shaped to provide a smoothly dimensioned exhaust valve seat to minimize losses, and thus enhance engine performance. 
           [0045]    In the figures of the drawing, like features may be illustrated with the same reference numerals, without further mention thereof. Further, the drawing figures are merely exemplary, and may contain various elements that might be present or omitted from actual implementations of certain embodiments. An attempt has been made to draw the figures in a way that illustrates at least those elements that are significant for an understanding of the invention. However, the drawings are generalized in the interest of clarity and conciseness. Notably, other elements or functional components for an improved combustion air inlet passageway, an improved hot exhaust gas exit passageway, and improved valve designs, may be utilized in order to provide useful performance enhancing components for aircraft engines, while within the literal scope and coverage of the claims set forth herein, or legal equivalents thereof. 
       
    
    
     DETAILED DESCRIPTION  
       [0046]    Attention is directed to  FIG. 1 , which illustrates a cylinder portion  24  and a head portion  26  which may be joined such as at joint  28  to provide a cylinder and head assembly  30  for an aircraft engine (not shown in its entirety). In various engine configurations, engine manufacturers may provide the cylinder potion  24  and the head portion  26  as a cylinder and head assembly (e.g. in the Lycoming Model O-360-C1G Parts Catalog as Part Number LW-12427, the “CYLINDER AND HEAD ASSY., Nitrided”). Alternately, the head portion  26  may be provided as a separate part from the cylinder itself. Those of skill in the art will recognize that the improvements described herein are described for use in the head portion  26 , regardless of whether a head portion is provided separately, or as part of a combined cylinder and head assembly  30 . Consequently, it should be understood that references to the “head” shall refer to the “head portion  26 ” regardless of whether or not a head is provided independently, or as a head portion of a cylinder and head assembly  30 , unless otherwise noted or made clear by context. However, various alternatives for parts supply including the inventive concepts described herein are set forth in this specification, including (a) the provision of a combined cylinder and head assembly  30 , and (b) the provision of a separable cylinder head or cylinder head portion  26  alone, wherein the cylinder head portion  26  is configured for attachment to a cylinder portion  24 . 
         [0047]    In the embodiment shown in  FIG. 1 , a parallel valve arrangement is provided, in that the intake valve  32  and the exhaust valve  34  are arranged in parallel fashion along their respective operative longitudinal axes  36  and  38 , respectively. Intake valve  32  has an intake valve seating face  40  that acts in concert with intake valve seat surface  42  to seal the intake during engine compression and exhaust cycles. Similarly, exhaust valve  34  has an exhaust valve seating face  44  that acts in concert with exhaust valve seat surface  46  to seal the exhaust valve during engine intake and compression cycles. Both the intake valve  32  and the exhaust valve  34  are operable in conventional fashion, and in conventional design configurations except as otherwise noted herein. 
         [0048]    As shown in the schematic view provided at  FIG. 22 , a cylinder and head assembly  30  for use on an aircraft engine is provided. The cylinder portion  24  includes a cylinder body  50 , having a cylinder bore  52  of diameter D, defined by inner sidewall  54 . The cylinder bore  52  is configured to operably confine a piston  56  of selected stroke distance  58  (i.e. operation is between top dead center  60  and bottom dead center  62 ), and thereby define a swept displacement volume DV. 
         [0049]    As seen in  FIG. 1  and in  FIG. 7 , adjacent the outer end  64  of cylinder body  50 , a head portion  26  is provided. The head portion  26  includes an inlet passageway  70  extending between an upstream inlet  72  and the intake valve seat surface  42 . At upstream inlet  72 , a flat intake gasket face  73  may be provided, and in an embodiment, in conventional fashion. The head portion  26  also includes an exhaust passageway  74  extending between an exhaust valve seat surface  46  and an exhaust outlet  76 . At exhaust outlet  76 , a flat exhaust gasket face  77  may be provided, and in an embodiment, in conventional fashion. 
         [0050]    The inlet passageway  70  has inlet passageway sidewalls  80  that cooperate to define, between the upstream inlet  72  and the intake valve seat surface  42 , an inlet passageway volume IPV for the inlet passageway  70 . In an embodiment, the inlet passageway volume IPV may be about thirty percent (30%), or less, of the swept displacement volume DV as described above. In an embodiment, the inlet passageway volume IPV may be about twenty eight percent (28%), or less, of the swept displacement volume DV. In an embodiment, the inlet passageway volume IPV may be about twenty five percent (25%) or less, of the swept displacement volume DV. 
         [0051]    As better seen in  FIG. 2 , in an embodiment, at the upstream inlet  72 , the inlet passageway  70  may be provided having in cross-section, a kidney shape, with the kidney shape having a first lobe  82  and a second lobe  84 . Further, as seen in  FIG. 2 , and also as clearly set forth in  FIG. 19 , the first lobe  82  and the second lobe  84  may be of uneven size. 
         [0052]    As may be seen  FIGS. 7 ,  8 ,  8 ,  10 ,  11 , and  12 , the inlet passageway sidewalls  80  may be provided in a cross-sectional shape corresponding to a surface reflecting the shapes at one or more of the cross-section locations as set forth in FIG.  7  and as described by the illustrations of such cross-section shape as set forth in  FIG. 8 ,  FIG. 9 ,  FIG. 10 , and  FIG. 11 . Further, in an embodiment, the inlet passageway sidewalls  80  may be provided in a cross-sectional shape having a curve fitted surface corresponding, at the intake valve seat surface  42 , to the shape set forth in  FIG. 12 . Further, in an embodiment, the inlet passageway sidewalls  80  may comprise, in cross-sectional shape, a curve-fitted shaped surface corresponding to the cross-sectional shapes shown at the cross-section locations noted in  FIG. 7  as illustrated in  FIGS. 8 ,  9 ,  10 , and  11 . In an embodiment, the cross-sectional shape at any one or more of the cross-sectional locations noted in  FIG. 7  may be as if taken orthogonally with respect to a centerline of the inlet passageway  70 . In further detail as indicated in  FIGS. 11 and 12 , the bottom end  90  of intake valve guide  92  may also be seen. 
         [0053]    Turning now to  FIG. 13 , the exhaust passageway  74  has exhaust passageway sidewalls  94  to define, between the exhaust valve seat surface  46  and the exhaust outlet  76 , an exhaust passageway volume EPV. In an embodiment, the exhaust passageway volume EPV may be sized to provide about seventy five percent (75%), or less, of the gas flow rate through the inlet passageway, when measured at equivalent pressure drop, as compared to an inlet passageway having the inlet passageway volume IPV as described above. When the inlet passageway volume IPV is varied, in various embodiments, the ratio of exhaust passageway volume EPV to the inlet passageway volume IPV may remain sized to provide about seventy five percent (75%) or less, of the gas flow rate through the inlet passageway, when measured at equivalent pressure drop, as compared to the corresponding inlet passageway volume IPV. 
         [0054]    As seen in  FIGS. 2 and 20 , at the exhaust outlet  76  (and as shown in  FIG. 18 , extending for a distance upstream from exhaust outlet  76 ) the exhaust passageway  74  may have, in an embodiment, a stylized-D cross-sectional shape. As more clearly seen in  FIG. 20 , in an embodiment, the stylized-D shape may further include a relatively flat portion  96  having rounded corners  98  and  100 . 
         [0055]    As may be appreciated from  FIGS. 13 ,  14 ,  15 ,  16 ,  17 , and  18 , in an embodiment, the exhaust passageway sidewalls  94  may be provided having a cross-sectional shape corresponding to a curve-fitted surface corresponding to one or more of the cross-section locations as set forth in  FIG. 15  and corresponding to the cross-sectional shapes illustrated in  FIGS. 15 ,  16 ,  17 , and  18 . In an embodiment, such cross-sectional shapes as illustrated in  FIGS. 15 ,  16 ,  17 , and  18 , may correspond to a cross section taken orthogonal to a centerline of exhaust passageway  74 . In an embodiment, the exhaust passageway sidewalls  94  may have, in cross-section shape, a curve fitted surface corresponding to a view of the exhaust valve seat surface  46  as set forth in  FIG. 14 . In an embodiment, the exhaust passageway sidewalls  94  may be provided having a cross-sectional shape corresponding to a curve-fitted surface corresponding to each of the cross-sectional shapes as illustrated in  FIGS. 15 ,  16 ,  17 , and  18 , for the corresponding cross-section locations as set forth in  FIG. 15 . In further detail as indicated in  FIGS. 14 and 15 , the bottom end  102  of exhaust valve guide  104  may also be seen. 
         [0056]    In order to further increase the performance of an engine utilizing the designs taught herein, additional refinements may be made to the configuration of intake valve  32 , and more particularly, the configuration of the intake valve seating face angle alpha (α), as noted in  FIG. 4 . As generally illustrated in  FIG. 3 , a prior art intake valve  105  might be provided with an intake valve seating face of about thirty degrees (30°). As more particularly shown in  FIG. 4A , a prior art intake valve such as the valve  105  shown in  FIG. 3  might have been provided having a seat face angle alpha (α) of about thirty degrees (30°) (as also indicated for reference in  FIG. 4A  along broken line  106 , for comparison to my current design configuration). However, I have found that adjustment of the intake valve seat face angle alpha (α) to about forty five degrees (45°), as indicated along broken line  108 , reduces directional change required for the air traversing the inlet passageway  70 , thus reducing the pressure loss through the inlet passageway  70 . More particularly, I have found that providing an intake valve  32  with an intake valve seating face  40  of length L 40  that is oriented at an angle alpha (α) of about forty five degrees (45°), plus or minus about three degrees) (3°), provides improved performance, as more fully explained elsewhere herein. In an embodiment, I have found that performance may be optimized by using an intake valve seating face  40  having an angle alpha (α) of about forty five degrees (45°), plus or minus about one point five degrees (1.5°). Of course, as noted in  FIG. 7 , in any of such embodiments as just described, the intake valve seat surface  42  should be oriented at an angle beta (β) complimentary to the angle alpha (α) of the intake valve  32  intake valve seating face  40 . Other details for a suitable intake valve  32  may be specified in a conventional manner, such as the radius R 32 , and the intake valve margin  110  height H 32 . 
         [0057]    In order to provide yet further increase in the performance of an engine utilizing the designs taught herein, additional refinements may be made to the configuration of exhaust valve  34 , and more particularly, to the configuration of the exhaust valve seating face  44 . In an embodiment, an exhaust valve seating face  44  may be provided having a length L 44  and disposed at an exhaust valve seating face angle theta (θ), as noted in  FIG. 6A . As generally indicated in  FIG. 5 , a prior art exhaust valve  111  may be provided with a exhaust valve seating face angle of about thirty degrees (30°). In an embodiment, as noted in  FIG. 6A , the exhaust valve seating face  44  of an exemplary exhaust valve  34  may be oriented at an angle theta (θ) of about forty five degrees (45°), plus or minus about three degrees (3°). The range for such an angle theta (θ) is of course from about forty two degrees (42°) to about forty eight degrees (48°). In an embodiment, the exhaust valve seating face  44  may be oriented at an angle theta (θ) of about forty five degrees (45°), plus or minus about one point five degrees (1.5°). The range for such an angle theta (θ) is of course from about forty three point five degrees (43.5°), to about forty six point five degrees (46.5°). As noted in  FIG. 13 , in any of such embodiments as just described, the exhaust valve seat surface  46  should be oriented at an angle sigma (Σ) complimentary to the angle theta (θ) of the exhaust valve seating face  44 . Other details for a suitable exhaust valve  34  may be specified in a conventional manner, such as the exhaust valve radius R 34 , and the exhaust valve margin  112  height H 34 . 
         [0058]    As mentioned above, in  FIG. 1 , the intake valve  32  and exhaust valve  34  may, in an embodiment, be oriented for parallel valve operation, wherein the operational longitudinal centerline  36  of the intake valve  32  and the operational longitudinal centerline  38  of the exhaust valve  34  are parallel. In such an embodiment, the intake valve seat surface  42  and the exhaust valve seat surface  46  are accordingly configured and located for parallel valve operation. 
         [0059]    Alternately, as illustrated in  FIG. 21 , in an embodiment, a head portion  126  may be configured using an intake valve  132  and an exhaust valve  134  in an angled valve configuration, wherein the operational longitudinal axis  136  of the intake valve  132 , and the operational longitudinal axis  138 , of the exhaust valve  134 , are not parallel, but angled, in the outward direction, away from each other, thus allowing additional combustion space volume  139  above a cylinder (not shown). Thus, in such a configuration, the intake valve seat surface  142  (adjacent the intake valve seating face  140 ) and the exhaust valve seat surface  146  (adjacent the exhaust valve seating face  144 ) are configured for such angled valve operation. 
         [0060]    A series of performance tests were conducted on a test bench, using air flow measurements (cubic feet per minute—“cfm”) on a static test piece which had been modified. Table 1.1 shows a set of baseline measurements conducted on a standard, stock Lycoming engine head. Then, inlet passageway  70  of the Lycoming head was modified, and performance at various flow conditions was measured. As noted in Table 1.2, modification of the inlet passageway  70  alone as described herein may be anticipated to provide an average gain of 3.36 horsepower, and a peak gain of 5.74 horsepower, for a typical Lycoming nominal 180 horsepower engine (of nominal 360 cubic inch displacement). For the same engine, when intake valve  32  (or  132 ) improvements are additionally provided, an average gain of 5.32 horsepower may be expected, and a peak gain of 8.19 horsepower is anticipated. Addition of improved intake valve seats and exhaust valve seats may further improve performance. 
         [0061]    Similarly, air flow bench testing was conducted on a test head portion having a modified exhaust passageway  74 . As noted in Table 2.1, a baseline set of measurements was conducted. Then, the Lycoming head portion  26  was evaluated after modification of the exhaust passageway  74 , and performance at various flow conditions was evaluated. With just modifications to the exhaust passageway  74 , an average horsepower gain of four percent (4%) is expected, and a peak horsepower gain of six percent (6%). For the same head portion with additional modifications to the exhaust valve  34 , average HP gain of ten percent (10%) is expected, and a peak gain of fourteen percent (14%). 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1.1 
               
             
             
               
                   
               
               
                 INTAKE: Stock Lycoming Head + Stock Lycoming Valve 
               
             
          
           
               
                 Valve Lift (in.) 
                 % of Reference 1   
                 Flow (CFM) 
                 BASELINE 
               
               
                   
               
             
          
           
               
                 0.200 
                 48 
                 91.46 
                   
               
               
                 0.250 
                 52 
                 99.09 
               
               
                 0.300 
                 56 
                 106.75 
               
               
                 0.350 
                 60 
                 114.33 
               
               
                 0.400 
                 63 
                 120.05 
               
               
                   
                   
                 Avg = 106.33 
               
               
                   
               
               
                   1 Bench test reference of 190.55 cfm at 10 inches of water pressure at the upstream inlet to the inlet passageway. Same for each of Table 1.1, Table 1.2, and Table 1.3. 
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1.2 
               
             
             
               
                   
               
               
                 INTAKE: Modified Lycoming Head + Stock Lycoming Valve 
               
             
          
           
               
                   
                 % of 
                   
                   
                   
               
               
                 Valve Lift (in.) 
                 Reference 
                 Flow (CFM) 
                 Improvement 
                 HP GAIN 
               
               
                   
               
             
          
           
               
                 0.200 
                 47 
                 89.56 
                   
                   
               
               
                 0.250 
                 54 
                 102.90 
               
               
                 0.300 
                 61/5 
                 117.19 
               
               
                 0.350 
                 67 
                 127.67 
               
               
                 0.400 
                 70 
                 133.39 
                 Peak Gain 
                 5.74 HP 
               
               
                   
                   
                 Avg = 114.14 
                 Avg. Gain 
                 3.36 HP 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1.3 
               
             
             
               
                   
               
               
                 INTAKE: Modified Lycoming Head + Modified Valve 
               
             
          
           
               
                   
                 % of 
                   
                   
                   
               
               
                 Valve Lift (in.) 
                 Reference 
                 Flow (CFM) 
                 Improvement 
                 HP GAIN 
               
               
                   
               
             
          
           
               
                 0.200 
                 46 
                 89.56 
                   
                   
               
               
                 0.250 
                 56.5 
                 102.90 
               
               
                 0.300 
                 65.5 
                 117.19 
               
               
                 0.350 
                 70.5 
                 127.67 
               
               
                 0.400 
                 73 
                 133.39 
                 Peak Gain 
                 8.19 HP 
               
               
                   
                   
                 Avg = 118.71 
                 Avg. Gain 
                 5.32 HP 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 2.1 
               
             
             
               
                   
               
               
                 EXHAUST: Stock Lycoming Head + Stock Lycoming Valve 
               
             
          
           
               
                 Valve Lift (in.) 
                 % of Reference 2   
                 Flow (CFM) 
                 BASELINE 
               
               
                   
               
               
                 0.200 
                 32 
                 60.98 
                   
               
               
                 0.250 
                 40 
                 76.22 
               
               
                 0.300 
                 45 
                 85.75 
               
               
                 0.350 
                 47 
                 89.56 
               
               
                 0.400 
                 50 
                 95.28 
               
               
                   
                   
                 Avg = 81.56 
               
               
                   
               
               
                   2 Same baseline reference for each of Table 2.1, Table 2.2, and Table 2.3. 
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2.2 
               
             
             
               
                   
               
               
                 EXHAUST: Modified Lycoming Head + Stock Valve 
               
             
          
           
               
                 Valve Lift (in.) 
                 % of Reference 
                 Flow (CFM) 
                 Improvement 
                 HP GAIN 
               
               
                   
               
             
          
           
               
                 0.200 
                 35 
                 66.69 
                   
                   
               
               
                 0.250 
                 41 
                 78.13 
               
               
                 0.300 
                 46 
                 87.65 
               
               
                 0.350 
                 48 
                 91.46 
               
               
                 0.400 
                 53 
                 100.98 
                 Peak Gain 
                 6% 
               
               
                   
                   
                 Avg = 84.98 
                 Avg. Gain 
                 4% 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2.3 
               
             
             
               
                   
               
               
                 EXHAUST: Modified Lycoming Head + Modified Valve 
               
             
          
           
               
                 Valve Lift (in.) 
                 % of Reference 
                 Flow (CFM) 
                 Improvement 
                 HP GAIN 
               
               
                   
               
             
          
           
               
                 0.200 
                 35 
                 66.69 
                   
                   
               
               
                 0.250 
                 42 
                 80.03 
               
               
                 0.300 
                 49 
                 93.37 
               
               
                 0.350 
                 54 
                 102.90 
               
               
                 0.400 
                 58 
                 110.52 
                 Peak Gain 
                 14% 
               
               
                   
                   
                 Avg = 90.70 
                 Avg. Gain 
                 10% 
               
               
                   
               
             
          
         
       
     
         [0062]    In addition to the use of head portion  26 , or cylinder and head assembly  30 , as explained above, in a new aircraft engine, the various components described herein may be utilized in retrofit or the rebuilding of existing aircraft engines, in order to increase performance thereof. Candidate engines for such a retrofit may be found in aircraft designed for use with an existing air cooled spark ignited piston engine with an original rated maximum horsepower, and where the engine have a plurality of individual cylinders each having cylinder head portions, and where the existing piston engine is mechanically designed for operation by intake of combustion air through original inlet air passageways in the cylinder head portions, providing an air fuel mixture to the individual cylinders, and combusting the fuel to produce hot exhaust gases that exit through original exhaust passageways in the cylinder head portions. An improvement in performance may be obtained by substituting, the existing cylinder head portions with replacement cylinder head portions  26 , wherein the replacement cylinder head portions  26  each providing an enhanced inlet air passageway  70  having reduced pressure drop during passage of combustion air therethrough as compared to pressure drop during passage of said combustion air through original air inlet passageways. Consequently, the use of the replacement cylinder head portions  26  provide an enhanced rated horsepower in excess of the original rated maximum horsepower for such an engine. 
         [0063]    In addition to providing an enhanced inlet passageway  70  in such replacement head portion  26  (or  126 ), an enhanced exhaust passageway  74  may be provided, having reduced pressure drop during passage of exhaust gases therethrough as compared to passage of hot exhaust gases through an original exhaust passageway. The use of such a replacement cylinder head portion  26 , or a cylinder and head assembly  30 , as appropriate given a particular engine design or retrofit requirement, provides an enhanced rated horsepower in excess of the original rated maximum horsepower. 
         [0064]    Yet further, improved inlet valve seats  150  (see  FIGS. 23 and 24 ), and improved exhaust valve seats  152  (see  FIGS. 25 and 26 ) may be provided to improve performance. A cylinder head  26  (or head  126  with angular configuration as seen in  FIG. 21 ), is provided for attachment to a cylinder body having a cylinder bore of diameter defined by a sidewall, and an outer end, the cylinder bore configured to operably confine a piston of selected stroke distance, and with the piston thereby define a swept displacement volume DV, as described herein above. In an embodiment, the intake valve seats may be provided as inserts  150 , as noted in  FIGS. 23 and 24 . In an embodiment, the exhaust valve seats may be provided as inserts  152 , as noted in  FIGS. 25 and 26 . In an embodiment, the exhaust valve seats have exhaust valve seat sidewalls  156 , which are configured for passage there through of exhaust gases. 
         [0065]    In an embodiment, the intake valve seat inserts  150  have intake valve seat sidewalls  154 , which are configured for passage there through of intake air. In an embodiment, the intake valve seat sidewalls  154  may be provided in cross-sectional shape as seen in  FIG. 23 , as an aerodynamically shaped surface having a plurality of intake valve seat facets respectively oriented at angles as defined at a respective cross-section location of each of the plurality of intake valve seat facets. For example, as shown in  FIG. 24 , the intake valve seat sidewalls  154  may comprise, in cross-sectional shape, a shaped surface having a plurality of facets I 1 , I 2 , I 3 , I 4 , I 5 , I 6 , or I 7 , respectively defined by one or more of the angles β 1 , β 2 , β 3 , β 4 , β 5 , β 6 , or β 7 , at the respective cross-section locations as set forth in  FIG. 24 . In an embodiment, angle β 1  may be at about fifteen degrees (15°). In an embodiment, angle β 1  may be at about fifteen degrees (15°). In an embodiment, angle β 2  may be at about thirty degrees (30°). In an embodiment, angle β 3  may be at about forty five degrees (45°). In an embodiment, angle β 4  may be at about sixty degrees (60°). In an embodiment, angle β 5  may be at about seventy five degrees (75°). In an embodiment, angle β 6  may be at about ninety degrees (90°). In an embodiment, angle β 7  may be at about one hundred five degrees (105°). 
         [0066]    For general description purposes, each facet may have an “in-plane” width described as its facet width F w . In an embodiment the facet I 2  associated with the angle β 2  may have a facet width F w  of about zero point one two inches (0.120″). 
         [0067]    In an embodiment, as seen in  FIG. 24 , the angle β 3  may be at about forty five degrees (45°), and the angle β 4  may be at about sixty degrees (60°), and the angle β 5  is about seventy five degrees (75°). In an embodiment, the facets I 3 , I 4 , I 5  associated with angles β 3 , β 4 , and β 5  respectively, may be of approximately equal facet width F w . 
         [0068]    In an embodiment, the intake valve seat sidewalls  154  may be configured, in cross-sectional shape, as a curve-fitted shaped surface corresponding approximately to the facets I 1 , I 2 , I 3 , I 4 , I 5 , I 6 , or I 7 , respectively defined by one or more of the angles β 1 , β 2 , β 3 , β 4 , β 5 , β 6 , or β 7 , all as noted above, at the respective cross-section locations as set forth in  FIG. 24 . In an embodiment, the intake valve seat sidewalls  154  may be configured, in cross-sectional shape, as a curve-fitted shaped surface corresponding to shapes defined by each of the angles β 1 , β 2 , β 3 , β 4 , β 5 , β 6 , or β 7 , at each of the respective cross-section locations as set forth in  FIG. 24 . In an embodiment, the intake valve seat sidewalls  154  may be configured, in cross-section shape, as a smooth curve fitted surface corresponding approximately to the facet surfaces defined by the series of angles β 1 , β 2 , β 3 , β 4 , β 5 , β 6 , or β 7 , at the respective cross-section locations as set forth in  FIG. 24 . 
         [0069]    Similarly, the exhaust valve seat  152  may comprise an insert having exhaust valve seat sidewalls  156 . In an embodiment, the exhaust valve seat inserts  152  have exhaust valve seat sidewalls  156 , which are configured for passage there through of exhaust gases. In an embodiment, the exhaust valve seat sidewalls  156  may be provided in cross-sectional shape as seen in  FIG. 25 , as an aerodynamically shaped surface having a plurality of exhaust valve seat facets respectively oriented at angles as defined at a respective cross-section location of each of the plurality of exhaust valve seat facets. For example, as shown in  FIG. 26 , the exhaust valve seat sidewalls  156  may comprise, in cross-sectional shape, a shaped surface having a plurality of facets E 1 , E 2 , E 3 , E 4 , E 5 , E 6 , or E 7 , respectively defined by one or more of the angles Σ 1 , Σ 2 , Σ 3 , Σ 4 , Σ 5 , Σ 6 , or Σ 7 , at the respective cross-section locations as set forth in  FIG. 26 . In an embodiment, angle Σ 1  may be at about fifteen degrees (15°). In an embodiment, angle Σ 2  may be at about thirty degrees. In an embodiment, angle Σ 3  may be at about forty five degrees (45°). In an embodiment, angle Σ 4  may be at about sixty degrees (60°). In an embodiment, angle Σ 5  may be at about seventy five degrees (75°). In an embodiment, angle Σ 6  may be at about ninety degrees (90°). In an embodiment, angle Σ 7  may be at about one hundred five degrees (105°). 
         [0070]    For general description purposes, each facet (E 1 , E 2 , E 3 , E 4 , E 5 , E 6 , E 7 , etc.) of an exhaust valve seat insert may have an “in -plane” width described as its facet width F w . In an embodiment the facet E 3  associated with the angle Σ 3  may have a facet width F w  of about zero point one five inches (0.150″). 
         [0071]    In an embodiment, as seen in  FIG. 24 , the angle Σ 4  may be at about sixty degrees (60°), and the angle Σ 5  may be at about seventy five degrees (75°). In an embodiment, the facets E 4  and E 5  associated with angles Σ 4  and Σ 5  respectively, may be of approximately equal facet width F w . 
         [0072]    In an embodiment, the exhaust valve seat sidewalls  156  may be configured, in cross-sectional shape, as a curve-fitted shaped surface corresponding approximately to the facets E 1 , E 2 , E 3 , E 4 , E 5 , E 6 , or E 7 , respectively defined by one or more of the angles Σ 1 , Σ 2 , Σ 3 , Σ 4 , Σ 5 , Σ 6 , or Σ 7 , all as noted above, at the respective cross-section locations as set forth in  FIG. 26 . In an embodiment, the intake valve seat sidewalls  154  may be configured, in cross-sectional shape, as a curve-fitted shaped surface corresponding to shapes defined by each of the angles Σ 1 , Σ 2 , Σ 3 , Σ 4 , Σ 5 , Σ 6 , or Σ 7 , at each of the respective cross-section locations as set forth in  FIG. 26 . In an embodiment, the intake valve seat sidewalls  154  may be configured, in cross-section shape, as a smooth curve fitted surface corresponding approximately to the facet surfaces defined by the series of angles Σ 1 , Σ 2 , Σ 3 , Σ 4 , Σ 5 , Σ 6 , or Σ 7 , at the respective cross-section locations as set forth in  FIG. 26 . 
         [0073]    As briefly noted above, the intake valve seat inserts  150  and the exhaust valve seat inserts  152  may be each provided in a parallel valve configuration engine. OR, the intake valve seat inserts  150  and exhaust valve seat inserts  152 , as just described above, may be provided for use in an angled valve configuration engine. 
         [0074]    It is to be appreciated that the various aspects, features, structures, and embodiments of a cylinder head, intake valve seats, and exhaust valve seats for internal combustion, spark ignition aircraft engines as described herein is a significant improvement in the state of the art. The components described are simple, reliable, and easy to use in lieu of existing cylinder head designs and components, whether on new engines, or as may be retrofitted on existing engines. Although only a few exemplary aspects and embodiments have been described in detail, various details are sufficiently set forth in the drawing figures and in the specification provided herein to enable one of ordinary skill in the art to make and use the invention(s), which need not be further described by additional writing. 
         [0075]    Importantly, the aspects, features, structures, and embodiments described and claimed herein may be modified from those shown without materially departing from the novel teachings and advantages provided, and may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, the various aspects and embodiments presented herein are to be considered in all respects as illustrative and not restrictive. As such, this disclosure is intended to cover the structures described herein and not only structural equivalents thereof, but also equivalent structures. Numerous modifications and variations are possible in light of the above teachings. The scope of the invention, as described herein is thus intended to include variations from the various aspects and embodiments provided which are nevertheless described by the broad meaning and range properly afforded to the language herein, as explained by and in light of the terms included herein, or the legal equivalents thereof.