Cylinder heads - Flow bench analysis
May 24, 2019 18:23:12 GMT
atlex, Dweenimus, and 5 more like this
Post by schercheeroo on May 24, 2019 18:23:12 GMT
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Introduction
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Aim
Collection and analysis of cylinder head flow data
Flow assessment and comparison of the Mk1(BP05) and Mk2(BP4W) non VVT cylinder head intake port flow
Intake to be flow tested with intake manifold fitted:
The BP05 tested with a 1995 Japanese Non EGR intake manifold
The BP4W tested with a late Mk2 European intake manifold aka square top or flat top manifold. Modifications were made to block off the EGR system.
The test results will be compared to a small data base compiled from flow test results found at sabre heads website.
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Contents
***************
Basic engine geometry
Cylinder head flow test equipment and test conditions
Cylinder head flow test procedure
Cylinder head flow measurement data and analysis
Analysis of existing cylinder head flow data from around the web
Summary and conclusion
Recommendation
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Basic engine geometry (BP05 and BP4W)
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Bore (mm) 83
Stroke (mm) 85
Rated Speed (rpm) 7000
Number of inlet valves per cylinder 2
Inner seat diameter [ISD] (mm) 29.5
Seat angle (°) 45
Valve head diameter (mm) 33
Inner seat area (sq. M) 0.001367
Mid Port area [Pm] (sq. M) 0.0016085(BP05) 0.0014577 (BP4W)
Port entry area [Pe] (sq. M) 0.0009745(BP05) 0.0010555 (BP4W
Camshaft geometry (BP05)
Max Lift (mm) 8.1
Duration (CA°) 245
Camshaft geometry (BP4W)
Max Lift (mm) 8.51 (includes 0.21mm lash for solid lifter)
Duration (CA°) 245
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Cylinder head flow test equipment and test conditions
**************************************************************
The flow bench uses a sharp edge orifice plate as the metering element with pressures measured at P1 (Barometric pressure), P2 (Pressure at cylinder head adapter exit) P3 (upper plenum pressure) and P4 (lower plenum pressure). The air flow is created by an air pump driven by a three phase motor.
Test conditions
7 kPa delta across the test piece (P1-P2)
Intake manifold fitted (throttle removed)
Radius fitted to entry of intake manifold (in place of throttle body)
Cylinder head adapter geometry
Bore (mm) 83 (1x Bore)
Length (mm) 127.5 (1.5x Stroke)
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Cylinder head flow test procedure
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Measurements taken at 1mm valve lift increments
Data collected over 10 seconds (averaged figure)
Valve opened to lift of L/D = 0.3 (10mm)
(L/D = Ratio of valve lift to valve head diameter)
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Cylinder head flow measurement data and analysis
********************************************************
Flow coefficient (Cf)
Cf = A measure of port flow efficiency. Compares actual port flow performance with that of a theoretically unrestricted port. Referenced to inner valve seat diameter.
Alpha K (Ak)
Ak = A measure of how effective the port is at filling the cylinder.
A good Alpha K number for a typical 4 valve chamber at a peak valve Lift is in excess of 0.16. An exceptional number is in excess of 0.22. Referenced to engine bore size.
Time area
The chart below displays flow area (Af) (i.e. annular ring or curtain area created when valves are lifted off the seat) over time the valve is open (in seconds) at an engine speed of 7000 rpm.
The lower two curves show the effective flow area (Aef). That is the flow area multiplied by the flow coefficient at the specific valve lift.
The area under the curves has been calculated:
BP05 (Af/s) 0.00000195
BP4W (Af/s) 0.00000227
BP4W (Af/s) is 14% greater than the BP05 (Af/s)
BP05 (Aef/s) 0.00000080
BP4W (Aef/s) 0.00000103
BP4W (Aef/s) is 22% greater than the BP05 (Aef/s)
Mach index (Mi)
The Mach index is useful for cylinder head analysis as it considers not only the camshaft profile and effective flow area, but also air flow due to piston motion.
The Mi calculation gives the ratio of the local sonic velocity to the air speed within the intake port. The calculation returns a pseudo Mach number that is integrated over one intake cycle.
The Mi gives an indication of the intake port's breathing ability, with a lower value indicating a more efficient port.
Empirical data (presented by Charles Fayette Taylor) has shown that volumetric efficiency starts to fall away at ~0.5 Mi, with 0.6 Mi given as the generally accepted not to exceed value.
The chart below shows the Mi / engine speed of both cylinder heads.
The BP05 achieves 0.5Mi at 6600rpm and 0.6Mi at 7940 rpm.
The BP4W achieves 0.5Mi at 7640 rpm and 0.6Mi at 9170rpm.
Port velocity
Another performance metric that must be assessed is the port velocity. If the port is too large the port velocity will be low. A consequence of the slower incoming air charge is poor combustion due to less in cylinder motion.
To asses port velocities the port is split into the entry portion (Pe), mid portion (Pm) and the throat (measured at the ISD).
The guidelines used are calculated as mean gas velocity at rated engine speed (7000 rpm). Good design practice guidelines for a high performance engine are 100-110 metres per second at the port entry, 90 to a 100 m/s in the mid port and 70 to 80 m/s at the port throat.
The velocities presented are near to the guideline values suggested above.
Therefore if modifying the port there would be little benefit gained from removing material from the port as this will only serve to reduce port velocity.
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Analysis of existing cylinder head flow data from around the web
*****************************************************************
A data set of flow data from 4V per cylinder heads has been compiled using data found at sabre-heads.co.uk
The comparisons made are Cf @ L/D = 0.25 and Ak @ L/D = 0.25
The data is displayed with the ratio of valve flow area / bore area on the x axis.
The MX5 1600 cylinder head data is displayed for comparison.
The Honda k20 (Type R) cylinder head is generally considered to be a well developed high performance engine. The data is highlighted here as a performance yardstick.
The data review shows flow coefficients range from low 0.5s to high 0.6s. The 1800cc MX5 cylinder heads display a mid level flow performance when compared to the wider population. There appears to be no correlation between Cf and valve area / engine bore area (R squared = 0.0). Therefore we can assume valve size and engine bore has little or no effect on port efficiency or that port flow efficiency is independent of basic engine geometry. It is more probable that the shape of the intake port will determine the flow efficiency.
The data review shows Ak values ranging from 0.14 to over 0.19. The 1800cc MX5 cylinder heads display a mid level performance when compared to the wider population. There is a clear positive correlation between Ak and valve flow area/bore area. Therefore we can assume that increasing valve size will increase the Alpha K value. That is the cylinder filling effectiveness can be improved by fitting a larger valve.
***********************************
Summary and conclusion
***********************************
A simple analysis has been made defining cylinder head intake port performance of two MX5 cylinder heads.
The BP4W head with flat top manifold has better flow coefficient showing an increase of 2% over the BP05 head at maximum valve lift.
The BP4W head with flat top manifold has also a better Alpha K value showing an increase of 0.6% over the BP05 head at maximum valve lift.
The better design of the BP4W port coupled with the higher lift of the BP4W's intake camshaft increases the effective flow area by 22% over the intake cycle when compared to the BP05 head and camshaft combo.
The flow improvement of the BP4W is validated by a Mach index of 0.458 versus the BP05 value of 0.529 at the rated speed of 7000 rpm.
The BP4W has potential to rev to over 9000 rpm before volumetric efficiency will begin to fall significantly. The volumetric efficiency of the BP05 head would begin to fall about 1000 rpm earlier.
A comparison of the MX5 cylinder head performance has been made to a small population of 4V per cylinder heads. Both the BP05 and BP4W head display an average level of flow performance when comparing the flow coefficient and Alpha K valves to the data set available.
The performance of both MX5 heads could be described as adequate, that is the performance is neither poor nor is it exceptional.
***********************************
Recommendation
***********************************
The analysis above indicates that the BP4W cylinder head is a significant performance upgrade over the BP05 cylinder head.
The BP4W should be considered for any high performance application, whether forced induction or naturally aspirated.
It is expected that performance of either head's intake ports could be improved with porting and valve seat work.
For maximum performance an increase in intake valve size should be considered to improve the cylinder filling capability.
Introduction
********************************************************
Aim
Collection and analysis of cylinder head flow data
Flow assessment and comparison of the Mk1(BP05) and Mk2(BP4W) non VVT cylinder head intake port flow
Intake to be flow tested with intake manifold fitted:
The BP05 tested with a 1995 Japanese Non EGR intake manifold
The BP4W tested with a late Mk2 European intake manifold aka square top or flat top manifold. Modifications were made to block off the EGR system.
The test results will be compared to a small data base compiled from flow test results found at sabre heads website.
****************
Contents
***************
Basic engine geometry
Cylinder head flow test equipment and test conditions
Cylinder head flow test procedure
Cylinder head flow measurement data and analysis
Analysis of existing cylinder head flow data from around the web
Summary and conclusion
Recommendation
**************************************
Basic engine geometry (BP05 and BP4W)
**************************************
Bore (mm) 83
Stroke (mm) 85
Rated Speed (rpm) 7000
Number of inlet valves per cylinder 2
Inner seat diameter [ISD] (mm) 29.5
Seat angle (°) 45
Valve head diameter (mm) 33
Inner seat area (sq. M) 0.001367
Mid Port area [Pm] (sq. M) 0.0016085(BP05) 0.0014577 (BP4W)
Port entry area [Pe] (sq. M) 0.0009745(BP05) 0.0010555 (BP4W
Camshaft geometry (BP05)
Max Lift (mm) 8.1
Duration (CA°) 245
Camshaft geometry (BP4W)
Max Lift (mm) 8.51 (includes 0.21mm lash for solid lifter)
Duration (CA°) 245
**************************************************************
Cylinder head flow test equipment and test conditions
**************************************************************
The flow bench uses a sharp edge orifice plate as the metering element with pressures measured at P1 (Barometric pressure), P2 (Pressure at cylinder head adapter exit) P3 (upper plenum pressure) and P4 (lower plenum pressure). The air flow is created by an air pump driven by a three phase motor.
Test conditions
7 kPa delta across the test piece (P1-P2)
Intake manifold fitted (throttle removed)
Radius fitted to entry of intake manifold (in place of throttle body)
Cylinder head adapter geometry
Bore (mm) 83 (1x Bore)
Length (mm) 127.5 (1.5x Stroke)
**************************************************************
Cylinder head flow test procedure
**************************************************************
Measurements taken at 1mm valve lift increments
Data collected over 10 seconds (averaged figure)
Valve opened to lift of L/D = 0.3 (10mm)
(L/D = Ratio of valve lift to valve head diameter)
********************************************************
Cylinder head flow measurement data and analysis
********************************************************
Flow coefficient (Cf)
Cf = A measure of port flow efficiency. Compares actual port flow performance with that of a theoretically unrestricted port. Referenced to inner valve seat diameter.
Alpha K (Ak)
Ak = A measure of how effective the port is at filling the cylinder.
A good Alpha K number for a typical 4 valve chamber at a peak valve Lift is in excess of 0.16. An exceptional number is in excess of 0.22. Referenced to engine bore size.
Time area
The chart below displays flow area (Af) (i.e. annular ring or curtain area created when valves are lifted off the seat) over time the valve is open (in seconds) at an engine speed of 7000 rpm.
The lower two curves show the effective flow area (Aef). That is the flow area multiplied by the flow coefficient at the specific valve lift.
The area under the curves has been calculated:
BP05 (Af/s) 0.00000195
BP4W (Af/s) 0.00000227
BP4W (Af/s) is 14% greater than the BP05 (Af/s)
BP05 (Aef/s) 0.00000080
BP4W (Aef/s) 0.00000103
BP4W (Aef/s) is 22% greater than the BP05 (Aef/s)
Mach index (Mi)
The Mach index is useful for cylinder head analysis as it considers not only the camshaft profile and effective flow area, but also air flow due to piston motion.
The Mi calculation gives the ratio of the local sonic velocity to the air speed within the intake port. The calculation returns a pseudo Mach number that is integrated over one intake cycle.
The Mi gives an indication of the intake port's breathing ability, with a lower value indicating a more efficient port.
Empirical data (presented by Charles Fayette Taylor) has shown that volumetric efficiency starts to fall away at ~0.5 Mi, with 0.6 Mi given as the generally accepted not to exceed value.
The chart below shows the Mi / engine speed of both cylinder heads.
The BP05 achieves 0.5Mi at 6600rpm and 0.6Mi at 7940 rpm.
The BP4W achieves 0.5Mi at 7640 rpm and 0.6Mi at 9170rpm.
Port velocity
Another performance metric that must be assessed is the port velocity. If the port is too large the port velocity will be low. A consequence of the slower incoming air charge is poor combustion due to less in cylinder motion.
To asses port velocities the port is split into the entry portion (Pe), mid portion (Pm) and the throat (measured at the ISD).
The guidelines used are calculated as mean gas velocity at rated engine speed (7000 rpm). Good design practice guidelines for a high performance engine are 100-110 metres per second at the port entry, 90 to a 100 m/s in the mid port and 70 to 80 m/s at the port throat.
The velocities presented are near to the guideline values suggested above.
Therefore if modifying the port there would be little benefit gained from removing material from the port as this will only serve to reduce port velocity.
*****************************************************************
Analysis of existing cylinder head flow data from around the web
*****************************************************************
A data set of flow data from 4V per cylinder heads has been compiled using data found at sabre-heads.co.uk
The comparisons made are Cf @ L/D = 0.25 and Ak @ L/D = 0.25
The data is displayed with the ratio of valve flow area / bore area on the x axis.
The MX5 1600 cylinder head data is displayed for comparison.
The Honda k20 (Type R) cylinder head is generally considered to be a well developed high performance engine. The data is highlighted here as a performance yardstick.
The data review shows flow coefficients range from low 0.5s to high 0.6s. The 1800cc MX5 cylinder heads display a mid level flow performance when compared to the wider population. There appears to be no correlation between Cf and valve area / engine bore area (R squared = 0.0). Therefore we can assume valve size and engine bore has little or no effect on port efficiency or that port flow efficiency is independent of basic engine geometry. It is more probable that the shape of the intake port will determine the flow efficiency.
The data review shows Ak values ranging from 0.14 to over 0.19. The 1800cc MX5 cylinder heads display a mid level performance when compared to the wider population. There is a clear positive correlation between Ak and valve flow area/bore area. Therefore we can assume that increasing valve size will increase the Alpha K value. That is the cylinder filling effectiveness can be improved by fitting a larger valve.
***********************************
Summary and conclusion
***********************************
A simple analysis has been made defining cylinder head intake port performance of two MX5 cylinder heads.
The BP4W head with flat top manifold has better flow coefficient showing an increase of 2% over the BP05 head at maximum valve lift.
The BP4W head with flat top manifold has also a better Alpha K value showing an increase of 0.6% over the BP05 head at maximum valve lift.
The better design of the BP4W port coupled with the higher lift of the BP4W's intake camshaft increases the effective flow area by 22% over the intake cycle when compared to the BP05 head and camshaft combo.
The flow improvement of the BP4W is validated by a Mach index of 0.458 versus the BP05 value of 0.529 at the rated speed of 7000 rpm.
The BP4W has potential to rev to over 9000 rpm before volumetric efficiency will begin to fall significantly. The volumetric efficiency of the BP05 head would begin to fall about 1000 rpm earlier.
A comparison of the MX5 cylinder head performance has been made to a small population of 4V per cylinder heads. Both the BP05 and BP4W head display an average level of flow performance when comparing the flow coefficient and Alpha K valves to the data set available.
The performance of both MX5 heads could be described as adequate, that is the performance is neither poor nor is it exceptional.
***********************************
Recommendation
***********************************
The analysis above indicates that the BP4W cylinder head is a significant performance upgrade over the BP05 cylinder head.
The BP4W should be considered for any high performance application, whether forced induction or naturally aspirated.
It is expected that performance of either head's intake ports could be improved with porting and valve seat work.
For maximum performance an increase in intake valve size should be considered to improve the cylinder filling capability.