Long Tubes....
Oct 23, 2008 | 03:18 AM
#21
I found this along time ago I just cant remember wht site I got it from interesting read:
"Exhaust valve duration. This is a question of relationship as well as airflow potential of your exhaust system. Know your exhaust to intake airflow ratio on your heads. If we assume 75% is the target, and we know that your heads flow 80%, we've got an exhaust potential that exceeds our need. In that case we need to decrease exhaust duration to artificially create a better scavenging wave in the exhaust (this is widely regarded as the most important factor in exhaust design). Of course headers have a HUGE effect on this because most scavenging and pressure waves propagate from the collector area which is directly affected by tube diameter and length (do you feel the math coming on again?). For arguments sake lets say the following guidelines define the optimum header diameter for a full length header on a V8. You can back calculate these numbers to determine the appropriate diameter for 4cyl, 6cyl, 12cyl, etc.
250-325 CID 1 5/8"
330-415 CID 1 3/4"
415-500 CID 1 7/8"
500-550 CID 2"
550-600 CID 2 1/8"
ADD 1/8" for every 50 CID over 600
For every 500 RPM over 6500 go up one primary size
These are rough guidelines that are obviously affected by many factors including materials, power adder, use, etc.
Now that you know your potential you can make a reasonable stab at exhaust duration. In general a single pattern camshaft makes more average power on a properly set up N/A combination. However, given that you have probably run into some constraint already, exhaust duration should usually be manipulated accordingly. It is not recommended to run any less than 4 degrees less than intake duration (reverse split camshaft), you should reduce primary diameter or put metal back in your heads (I know it's not possible, but you now know why your head work was so important). You should also not increase the duration of the exhaust more than 4 over the intake on an N/A motor. You're power adder is the next thing to address if you've got turbo, supercharger, or nitrous your motor has a LOT easier time getting air in than it has getting it to come out. Increase your exhaust duration 2 degrees for every 100 hp extra air your motor will see on the intake. This should be limited to a maximum of 10 degrees over the intake duration. If you have a turbo car, don't go too far with this or you'll start shoving too much exhaust back into the combustion chamber (this is a great way to increase detonation potential in your motor). If you've got a turbo motor this number will also be able to manipulate EGT which is important if you want to keep from liquefying your exhaust valves."
"Exhaust valve duration. This is a question of relationship as well as airflow potential of your exhaust system. Know your exhaust to intake airflow ratio on your heads. If we assume 75% is the target, and we know that your heads flow 80%, we've got an exhaust potential that exceeds our need. In that case we need to decrease exhaust duration to artificially create a better scavenging wave in the exhaust (this is widely regarded as the most important factor in exhaust design). Of course headers have a HUGE effect on this because most scavenging and pressure waves propagate from the collector area which is directly affected by tube diameter and length (do you feel the math coming on again?). For arguments sake lets say the following guidelines define the optimum header diameter for a full length header on a V8. You can back calculate these numbers to determine the appropriate diameter for 4cyl, 6cyl, 12cyl, etc.
250-325 CID 1 5/8"
330-415 CID 1 3/4"
415-500 CID 1 7/8"
500-550 CID 2"
550-600 CID 2 1/8"
ADD 1/8" for every 50 CID over 600
For every 500 RPM over 6500 go up one primary size
These are rough guidelines that are obviously affected by many factors including materials, power adder, use, etc.
Now that you know your potential you can make a reasonable stab at exhaust duration. In general a single pattern camshaft makes more average power on a properly set up N/A combination. However, given that you have probably run into some constraint already, exhaust duration should usually be manipulated accordingly. It is not recommended to run any less than 4 degrees less than intake duration (reverse split camshaft), you should reduce primary diameter or put metal back in your heads (I know it's not possible, but you now know why your head work was so important). You should also not increase the duration of the exhaust more than 4 over the intake on an N/A motor. You're power adder is the next thing to address if you've got turbo, supercharger, or nitrous your motor has a LOT easier time getting air in than it has getting it to come out. Increase your exhaust duration 2 degrees for every 100 hp extra air your motor will see on the intake. This should be limited to a maximum of 10 degrees over the intake duration. If you have a turbo car, don't go too far with this or you'll start shoving too much exhaust back into the combustion chamber (this is a great way to increase detonation potential in your motor). If you've got a turbo motor this number will also be able to manipulate EGT which is important if you want to keep from liquefying your exhaust valves."
Oct 23, 2008 | 08:12 PM
#22
I found this along time ago I just cant remember wht site I got it from interesting read:
"Exhaust valve duration. This is a question of relationship as well as airflow potential of your exhaust system. Know your exhaust to intake airflow ratio on your heads. If we assume 75% is the target, and we know that your heads flow 80%, we've got an exhaust potential that exceeds our need. In that case we need to decrease exhaust duration to artificially create a better scavenging wave in the exhaust (this is widely regarded as the most important factor in exhaust design). Of course headers have a HUGE effect on this because most scavenging and pressure waves propagate from the collector area which is directly affected by tube diameter and length (do you feel the math coming on again?). For arguments sake lets say the following guidelines define the optimum header diameter for a full length header on a V8. You can back calculate these numbers to determine the appropriate diameter for 4cyl, 6cyl, 12cyl, etc.
250-325 CID 1 5/8"
330-415 CID 1 3/4"
415-500 CID 1 7/8"
500-550 CID 2"
550-600 CID 2 1/8"
ADD 1/8" for every 50 CID over 600
For every 500 RPM over 6500 go up one primary size
These are rough guidelines that are obviously affected by many factors including materials, power adder, use, etc.
Now that you know your potential you can make a reasonable stab at exhaust duration. In general a single pattern camshaft makes more average power on a properly set up N/A combination. However, given that you have probably run into some constraint already, exhaust duration should usually be manipulated accordingly. It is not recommended to run any less than 4 degrees less than intake duration (reverse split camshaft), you should reduce primary diameter or put metal back in your heads (I know it's not possible, but you now know why your head work was so important). You should also not increase the duration of the exhaust more than 4 over the intake on an N/A motor. You're power adder is the next thing to address if you've got turbo, supercharger, or nitrous your motor has a LOT easier time getting air in than it has getting it to come out. Increase your exhaust duration 2 degrees for every 100 hp extra air your motor will see on the intake. This should be limited to a maximum of 10 degrees over the intake duration. If you have a turbo car, don't go too far with this or you'll start shoving too much exhaust back into the combustion chamber (this is a great way to increase detonation potential in your motor). If you've got a turbo motor this number will also be able to manipulate EGT which is important if you want to keep from liquefying your exhaust valves."
"Exhaust valve duration. This is a question of relationship as well as airflow potential of your exhaust system. Know your exhaust to intake airflow ratio on your heads. If we assume 75% is the target, and we know that your heads flow 80%, we've got an exhaust potential that exceeds our need. In that case we need to decrease exhaust duration to artificially create a better scavenging wave in the exhaust (this is widely regarded as the most important factor in exhaust design). Of course headers have a HUGE effect on this because most scavenging and pressure waves propagate from the collector area which is directly affected by tube diameter and length (do you feel the math coming on again?). For arguments sake lets say the following guidelines define the optimum header diameter for a full length header on a V8. You can back calculate these numbers to determine the appropriate diameter for 4cyl, 6cyl, 12cyl, etc.
250-325 CID 1 5/8"
330-415 CID 1 3/4"
415-500 CID 1 7/8"
500-550 CID 2"
550-600 CID 2 1/8"
ADD 1/8" for every 50 CID over 600
For every 500 RPM over 6500 go up one primary size
These are rough guidelines that are obviously affected by many factors including materials, power adder, use, etc.
Now that you know your potential you can make a reasonable stab at exhaust duration. In general a single pattern camshaft makes more average power on a properly set up N/A combination. However, given that you have probably run into some constraint already, exhaust duration should usually be manipulated accordingly. It is not recommended to run any less than 4 degrees less than intake duration (reverse split camshaft), you should reduce primary diameter or put metal back in your heads (I know it's not possible, but you now know why your head work was so important). You should also not increase the duration of the exhaust more than 4 over the intake on an N/A motor. You're power adder is the next thing to address if you've got turbo, supercharger, or nitrous your motor has a LOT easier time getting air in than it has getting it to come out. Increase your exhaust duration 2 degrees for every 100 hp extra air your motor will see on the intake. This should be limited to a maximum of 10 degrees over the intake duration. If you have a turbo car, don't go too far with this or you'll start shoving too much exhaust back into the combustion chamber (this is a great way to increase detonation potential in your motor). If you've got a turbo motor this number will also be able to manipulate EGT which is important if you want to keep from liquefying your exhaust valves."
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