Camshaft and reversion?
09-12-2003 | 08:08 PM
#31
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From: ohio
And, its not just how long the intake and exhaust valves are open together, its also what the piston is doing at that time. Some cams and timing will actually create a cloud of gas vapor above the carb at idle. Its also a condition called reversion.
09-13-2003 | 10:22 AM
#32
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Joined: Feb 2001
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From: Lemont, IL
Just a little more info from the cam card,
Valve timing at .006:
open close
intake 29 BTDC 61 ABDC
exhaust 69 BBDC 21 ATDC
These specs are for cam installed at 106 center line.
A little lesson regarding this info would be appreciated.
Paul
Valve timing at .006:
open close
intake 29 BTDC 61 ABDC
exhaust 69 BBDC 21 ATDC
These specs are for cam installed at 106 center line.
A little lesson regarding this info would be appreciated.
Paul
Last edited by pb; 09-13-2003 at 05:26 PM.
09-13-2003 | 03:12 PM
#33
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From: Melbourne, Florida
This could be an online ITT tech course. Great info, but one question. Are we just splitting hairs by trying to push the cam specs just below reversion levels or is the HP gains that significant. Is there a HP calculator for cams and doesn't intake, carb and heads have as much to do with cam characteristics as exhaust? Aren't they all support each other. How much HP gain can be achieved from stock cam to performance?
09-13-2003 | 04:22 PM
#34
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From: Deland, Florida
Originally posted by nauticaL ILLUSIONS
This could be an online ITT tech course. Great info, but one question. Are we just splitting hairs by trying to push the cam specs just below reversion levels or is the HP gains that significant. Is there a HP calculator for cams and doesn't intake, carb and heads have as much to do with cam characteristics as exhaust? Aren't they all support each other. How much HP gain can be achieved from stock cam to performance?
This could be an online ITT tech course. Great info, but one question. Are we just splitting hairs by trying to push the cam specs just below reversion levels or is the HP gains that significant. Is there a HP calculator for cams and doesn't intake, carb and heads have as much to do with cam characteristics as exhaust? Aren't they all support each other. How much HP gain can be achieved from stock cam to performance?
When ya comin' back out to play?
09-13-2003 | 05:49 PM
#35
MarineKinetics
Joined: Oct 2002
Posts: 942
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From: Rochester, NY
nautical ILLUSIONS,
Because reversion is inherent in nearly all engines the object is not to eliminate the effect but to keep it within acceptable levels depending upon the environment or application. When a passenger car is idling smoothly essentially you are "hearing" very low levels of reversion due to a limited number of degrees of crankshaft rotation where the intake and exhaust valve are open at the same time. However when you listen to a sprint car or pro stocker that " choppy" idle is caused by camshaft with a generous amount of overlap. The difference here is the sprint/ pro stocker ( cammed primarily for relatively narrow power bands) doesn't have to idle with water being introduced into the exhaust path providing that water an opportunity to "revert" back into the combustion chamber. The challenge in the design and selection of marine camshafts is managing the additional variable in addition to the proper component selection.
Hope this helps,
Bob
Because reversion is inherent in nearly all engines the object is not to eliminate the effect but to keep it within acceptable levels depending upon the environment or application. When a passenger car is idling smoothly essentially you are "hearing" very low levels of reversion due to a limited number of degrees of crankshaft rotation where the intake and exhaust valve are open at the same time. However when you listen to a sprint car or pro stocker that " choppy" idle is caused by camshaft with a generous amount of overlap. The difference here is the sprint/ pro stocker ( cammed primarily for relatively narrow power bands) doesn't have to idle with water being introduced into the exhaust path providing that water an opportunity to "revert" back into the combustion chamber. The challenge in the design and selection of marine camshafts is managing the additional variable in addition to the proper component selection.
Hope this helps,
Bob
09-13-2003 | 10:08 PM
#36
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From: Melbourne, Florida
cuda, how are ya. Ya this has been a dismal boat season. A total write off actually, but next year I'll be ready. I got a pair of Bravos on the way and I think I'll throw a pair of ext. boxes on them. That with a few engine massages and that shouldl be 80+ for me. You'll have to take a rip over this way some time and we'll rip up to Daytona.
